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Klik på et bogstav for at se de begreber, der er forklaringer til.
- ACE-hæmmere: Angiotensin Converting Enzyme hæmmere. ACE-hæmmere nedsætter aktiviteten af renin-angiotensin-aldosteron-systemet ved at hæmme omdannelsen af angiotensin I til II, hvorved universel vasodilatation uden sympatikusaktivering indtræder og medfører fald i blodtrykket. Anvendes typisk mod forhøjet blodtryk og hjerteinsufficiens.
- Antacida: Stoffer der neutraliserer syre produceret i mavesækken. Eller: Syreneutraliserende stoffer, der medfører neutralisering af mavesækkens pH.
- AUC: Area under the curve. Det grafiske areal under en plasmakoncentrations-tids-kurve for et lægemiddel. AUC bruges til at beskrive, hvordan kroppen eksponeres for et givent lægemiddel og anvendes til at estimere biotilgængeligheden og clearence.
- BID: Medicinsk forkortelse for bis in die = to gange dagligt.
- Biotilgængelighed, F: Den del af et oralt administreret lægemiddel, der i forhold til en intravenøs dosis når det systemiske kredsløb. Omfatter også den hastighed, hvormed dette sker. Biotilgængelighed omfatter både absorptionen over tarmvæggen (absorptionen sensu strictiori) og en evt. førstepassagemetabolisme.
- Bredspektret antibiotika: Antibiotika med virkning på et bredt spektrum af mikroorganismer, i modsætning til smalspektrede antibiotika, der kun er virksomme over for specifikke typer af mikroorganismer.
- Clearance (Cl): Forholdet mellem et lægemiddels (eller andet stofs) eliminationshastighed (mængde per tidsenhed) og dets koncentration i plasma (eller blod).
Clearance er konstant, dvs. koncentrations-uafhængig, for stoffer, der elimineres efter en 1. ordens-reaktion. Clearance bestemmer sammen med fordelingsrummet halveringstiden. Clearance fra forskellige eliminationsorganer er additiv.
- Cmax: Den maksimale koncentration i plasma, der opnås efter lægemiddelindgift.
Ved i.v. indgift er Cmax lig Co, mens Cmax efter peroral indgift oftest først opnås efter 1-2 timer (tmax).
- CYP P450: Cytochrom-P450. Enzymsystem, som metaboliserer adskillige lægemidler via oxidering.
Oxidering udgør den kvantitativt dominerende eliminationsvej for lægemidler. CYP-enzymerne forekommer i særlig høj koncentration i leveren.
- Fald i clearance: Lægemidlet tager længere tid at få renset ud af kroppen.
- Halveringstid, t1/2: Den tid, det tager organismen (efter fordeling) at eliminere halvdelen af den tilbageværende mængde lægemiddel i kroppen.
Størrelsen er konstant og koncentrationsuafhængig for lægemidler med 1. ordens-elimination.
- Hepatisk: Vedr. leveren.
- Hypertension: Forhøjet blodtryk.
- Hypoglykæmi: Lavt blodsukker. Symptomer optræder ofte ved blodsukker lavere end 2,5 mmol/L.
- Hypotension: Lavt blodtryk.
- Hypothyreose: Nedsat funktion af skjoldbruskkirtlen som fører til nedsat dannelse af hormon (thyroxin) og dermed for lavt stofskifte.
- Inducerende lægemiddel: Når et lægemiddel forårsager øget omsætning af et andet lægemiddel via induktion af f.eks. CYP450.
- Induktion: Øget omsætning af et lægemiddel via induktion af f.eks. CYP450.
- INR: International normalized ratio. INR er en standardiseringsmetode til sammenligning af koagulationstider (protrombintider, PT). INR er således et mål for blodets evne til at koagulere.
INR har til formål at minimere forskellene mellem tromboplastinreagenser ved hjælp af en kalibreringsproces, hvor alle kommercielle tromboplastiner sammenlignes med et internationalt referencemateriale. INR beregnes således: INR=((Patient PT)/(Middel normal PT))^ISI , og fortæller dermed hvor lang koagulationstiden er i forhold til den normale koagulationstid.
- ISI: International Sensitivity Index. Protrombintid målt med forskellige tromboplastiner kan ikke sammenlignes direkte med hinanden, f.eks. fordi sensitiviteten over for koagulationsfaktorer kan variere. For at få koagulationstider, der er så sammenlignelige som muligt, godkendte Verdenssundhedsorganisationen (WHO) i 1983 en standard reference-tromboplastin. Alle producenter af tromboplastin skal kalibrere deres reagens over for WHOs standard. Den fundne værdi betegnes International Sensitivity Index (ISI), og bruges til at beregne INR.
- Iskæmi: Ophævet eller nedsat blodforsyning af et væv i forhold til dets behov.
- Isoenzymer: Forskellige udtryksformer for et enzym. Opstår pga. af forskellige allelle gener. Eksempler ses inden for det lægemiddelomsættende system CYP450, hvor isoenzymer f.eks. er 2D6, 3A4 og 2C9.
- Kasuistik: I lægevidenskab en offentliggjort beskrivelse af et enkelt eller få sygdomstilfælde (casus (lat.): ”tilfælde, sag”).
- Lipidsænkende lægemidler: Lægemidler, der sænker visse af blodets fedtstoffer – kolesterolsænkende.
- Metabolisme: Metabolisme eller stofskifte er en generel betegnelse for den biokemiske omsætning af kemiske forbindelser i den levende organisme og dens celler. Bruges synonymt med biotransformation.
- P-gp: Permeability glycoprotein. P-gp er et cellemembran-protein, som er tilstede i epithelceller i bl.a. tarm, lever og nyrer, hvor det transporterer fremmede substanser fra blodet og ud i hhv. tarmen, galdegange og nyretubuli.
- Plasma: Plasma er den fraktion af blodet, der ikke indeholder celler. Plasma indeholder forskellige næringsstoffer, hormoner, antistoffer, koagulationsfaktorer og salte. 95% af plasma består af vand.
- PO: Per os. Via munden.
- PN medicinering: Pro re nata medicinering. Medicin, der gives efter behov.
- PT: Protrombintid. Tiden, det tager plasma at koagulere, efter tilsætning af tromboplastin (også kaldet tissue factor). Protrombintiden bruges til at vurdere blodets koagulationsevne, og anvendes især til monitorering af antikoagulationsbehandling.
- qd: Quaque die. Hver dag.
- QID: Quater in die. Fire gange dagligt.
- Renal: (af lat. renalis), vedr. nyrerne.
- Respirationsdepression: Respirationsdepression (også kaldet hypoventilation) er når frekvensen eller dybden af respirationen er utiltrækkelig til at opretholde den nødvendige gasudveksling i lungerne.
- Serotonergt syndrom: Et symptomkompleks, der skyldes overstimulering i centralnervesystemet med serotonergt aktive substanser. Symptomerne er muskelrykninger, skælven, kvalme, diarré, sved og forvirring.
- Serum: Plasma uden koagulationsfaktorer.
- SID: Semel in die. Én gang dagligt.
- SmPC: SmPC står for Summary of Product Characteristics, og er det engelske udtryk for produktresumé.
- TID: Ter in die. Tre gange dagligt.
- tmax: Det tidspunkt, hvor den maksimale plasmakoncentration af et lægemiddel indtræder. Des hurtigere absorptionshastighed, des mindre tmax.
- Total clearance: Summen af hepatisk og renal clearance. I hvilken grad disse fraktioner bidrager afhænger af, om lægemidlet primært udskilles renalt eller også undergår fase I (f.eks. via CYP) og fase II (f.eks. glukuronidering) biotransformation i leveren.
- UGT: Uridine 5'-diphospho-glucuronosyltransferase, eller UDP- glucuronosyltransferase. Glucuronyltransferaser er enzymer, som foretager konjugering (glucuronidering) af mange lægemidler og lægemiddelmetabolitter, hvorved de omdannes til stoffer, der er lettere at udskille.
- Vasodilatation: Udvidelse af kar.
- Vasokonstriktion: Sammentrækning af kar.
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Formålet med Interaktionsdatabasen er at gøre behandlingen med lægemidler mere effektiv og sikker, og fremme kvaliteten i patientbehandlingen, herunder bidrage til rationel farmakoterapi. Det har været til hensigt at udvikle et redskab, der er let at anvende i den kliniske hverdag og, hvor der på højt fagligt niveau er skabt konsensus om rekommandationer og beskrivelser af interaktioner mellem lægemidler.
Interaktionsdatabasens primære evidensgrundlag er offentligt publicerede, peer-reviewed original interaktionslitteratur (kliniske studier udført på mennesker og kasuistikker) publiceret i PubMed og Embase.
Der vil således kunne forekomme uoverensstemmelse mellem andre opslagsværker, som er opbygget efter andre principper og evidenskriterier.
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Etableringen af Interaktionsdatabasen var et fælles projekt mellem Danmarks Apotekerforening, Den Almindelige Danske Lægeforening, Dansk Lægemiddel Information A/S og Institut for Rationel Farmakoterapi. En projektleder og 2 farmaceuter stod for opbygningen af databasen bistået af et fagligt videnskabeligt udvalg. Desuden har der været tilknyttet eksperter indenfor forskellige fagområder. Efter en årrække under Sundhedsstyrelsen overtog Lægemiddelstyrelsen i 2015 driften og vedligeholdelsen af databasen.
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Vær opmærksom på, at alle anbefalinger på Interaktionsdatabasen.dk er vejledende.
Hjemmesiden giver desuden ikke oplysninger om bivirkninger ved hvert enkelt præparat. Her henviser vi til indlægssedlen i det enkelte præparat eller til Lægemiddelstyrelsens produktresuméer.
Der kan forekomme bivirkninger, du ikke kan finde informationer om her. Dem vil vi opfordre dig til at indberette til Lægemiddelstyrelsen. Det kan du gøre på:
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I denne database er lægemiddelinteraktion defineret som en ændring i enten farmakodynamikken og/eller farmakokinetikken af et lægemiddel forårsaget af samtidig behandling med et andet lægemiddel.
Interaktionsdatabasen medtager farmakodynamiske interaktioner, der ikke er umiddelbart indlysende additive (fx med forskellig virkningsmekanisme), og som kan have væsentlig klinisk betydning.
Andre faktorer, som interagerer med eller ændrer lægemiddelvirkningen så som næringsmidler (f.eks. fødemidler og kosttilskud) og nydelsesmidler (f.eks. alkohol og tobak), er ikke medtaget. Dog er medtaget lægemiddelinteraktioner med grapefrugtjuice, tranebærjuice og visse naturlægemidler.
Interaktionsdatabasens primære evidensgrundlag er offentligt publicerede, peer-reviewed original interaktionslitteratur (kliniske studier udført på mennesker samt kasuistikker) publiceret i PubMed og Embase. Desuden er interaktioner hvor data er beskrevet i produktresuméer medtaget.
I Interaktionsdatabasen findes fem forskellige symboler:
- Det røde symbol (tommelfingeren, der peger nedad) betyder, at den pågældende præparatkombination bør undgås. Denne anbefaling bliver givet i tilfælde hvor det vurderes, at den kliniske betydning er udtalt, og hvor dosisjustering ikke er mulig, eller hvis der er ligeværdige alternativer til et eller begge af de interagerende stoffer. Det røde symbol vælges også i tilfælde, hvor der vurderes at være ringe dokumenteret effekt af et eller begge stoffer, (hvor anvendelse derfor ikke findes strengt nødvendig), f.eks. for visse naturlægemidler.
- Det gule symbol (den løftede pegefinger) betyder, at kombinationen kan anvendes under visse forholdsregler. Denne anbefaling gives i tilfælde, hvor det vurderes, at den kliniske betydning er moderat til udtalt, samtidig med at den negative kliniske effekt af interaktionen kan modvirkes, enten gennem ned- eller opjustering af dosis, eller ved at forskyde indtagelsestidspunktet for det ene præparat. Anbefalingen gives også, hvis det vurderes, at kombinationen kan anvendes under forudsætning af øget opmærksomhed på effekt og/eller bivirkninger.
- Det grønne symbol (tommelfingeren, der peger opad) betyder, at kombinationen kan anvendes. Denne anbefaling gives i tilfælde, hvor det vurderes, at den kliniske betydning er uvæsentlig eller ikke tilstede.
- Det blå symbol (udråbstegnet) fremkommer i tilfælde, hvor der søges på et specifikt præparat eller en præparatkombination, som ikke findes beskrevet i Interaktionsdatabasen, men hvor der findes andre beskrevne interaktioner mellem stoffer i stofgruppen, som muligvis kan være relevante for søgningen.
- Det grå symbol (spørgsmålstegnet) fremkommer i tilfælde, hvor der er søgt på et præparat eller en præparatkombination, som (endnu) ikke er beskrevet i Interaktionsdatabasen, og hvor der heller ikke findes beskrivelser af andre præparatkombinationer mellem de to stofgrupper. En manglende beskrivelse er ensbetydende med, at Lægemiddelstyrelsen ikke har kendskab til videnskabelige undersøgelser, der undersøger en interaktion mellem den pågældende præparatkombination, og heller ikke til kasuistiske beskrivelser af en mulig interaktion. Der kan også være tale om en kombination, hvor der ikke kan drages konklusioner på baggrund af nuværende viden.
Opdatering af databasens faglige indhold foregår via litteratursøgninger som leveres via Det Kongelige Bibliotek. Litteratursøgningerne er struktureret efter veldefinerede søgekriterier og bliver løbende evalueret. Endvidere foretages yderligere håndsøgning i referencelister som kvalitetssikring af litteratursøgningerne.
Databasen bliver opdateret løbende.
Lægemiddelstyrelsens enhed Regulatorisk & Generel Medicin står for opdatering og vedligehold af Interaktionsdatabasens indhold.
Vedligehold og opdatering af databasen foretages af den faglige arbejdsgruppe, som består af 1 akademisk medarbejder og 2 studerende.
Arbejdsgruppen samarbejder med en deltidsansat speciallæge i klinisk farmakologi omkring den kliniske vurdering af lægemiddelinteraktionerne.
Interaktionsdatabasen er et opslagsværktøj, der beskriver evidensbaserede interaktioner, det vil sige interaktioner, der er dokumenteret ved publicerede kliniske studier og/eller kasuistikker. Der vil således kunne forekomme uoverensstemmelse mellem andre opslagsværker, som er opbygget efter andre principper og evidenskriterier.
Der inkluderes kun interaktioner fra offentligt publicerede, peer-reviewed original interaktionslitteratur (kliniske studier udført på mennesker samt kasuistikker) publiceret i PubMed og Embase. Desuden er interaktioner hvor data er beskrevet i produktresuméer også medtaget. Det tilstræbes at databasen opdateres snarest efter publicering, men der kan forekomme forsinkelser.
Interaktionsdatabasen beskriver interaktioner for markedsførte lægemidler, naturlægemidler samt stærke vitaminer og mineraler. I interaktionsbeskrivelserne skelnes som udgangspunkt ikke mellem forskellige dispenseringsformer. For udvalgte lægemidler skelnes dog mellem dermatologiske og systemiske formuleringer. Handelsnavnene for stærke vitaminer og mineraler, naturlægemidler samt lægemidler som ikke figurerer på medicinpriser.dk (dvs. SAD præparater) kan ikke findes på interaktionsdatabasen.
Interaktionsdatabasen omhandler ikke kosttilskud, vacciner, parenteral ernæring, elektrolytvæsker, lægemidler uden systemisk effekt og priktest (ALK).
Ja, du kan slå både lægemidler, naturlægemidler, stærke vitaminer, mineraler og enkelte frugtjuice op.
Naturlægemidler er en særlig gruppe lægemidler, der typisk indeholder tørrede planter eller plantedele, udtræk af planter eller andre naturligt forekommende bestanddele. Naturlægemidler er i lovgivningen defineret som "lægemidler, hvis indholdsstoffer udelukkende er naturligt forekommende stoffer i koncentrationer, der ikke er væsentligt større end dem, hvori de forekommer i naturen". Naturlægemidler skal godkendes af Lægemiddelstyrelsen inden de må sælges.
Stærke vitaminer og mineraler er en gruppe lægemidler, hvis indholdsstoffer udelukkende er vitaminer og/eller mineraler, og hvor indholdet af vitamin eller mineral er væsentligt højere end det normale døgnbehov hos voksne mennesker. Stærke vitaminer og mineraler kan kun godkendes til at forebygge og helbrede såkaldte mangeltilstande (og altså ikke til at behandle sygdomme). Stærke vitaminer og mineraler må kun sælges i Danmark, hvis de er godkendt af Lægemiddelstyrelsen.
Ja, du kan søge på så mange lægemidler/indholdsstoffer, du ønsker samtidig. Det gør du ved at bruge søgeboksen til højre på forsiden med overskriften ”Søg på flere præparater i kombination”. Her kan du tilføje flere felter med knappen nederst. Hvis du søger på kombinationer med mere end to slags lægemidler/indholdsstoffer, skal du være opmærksom på, at du ikke kun får ét resultat, men et antal 1+1 kombinationer. Et eksempel: Hvis du søger på samtidig brug af en p-pille, et blodtrykssænkende lægemiddel og et sovemiddel, får du 3 mulige resultater:
A: kombinationen af p-pille og blodtrykssænkende lægemiddel
B: kombinationen af p-pille og sovemiddel
C: kombinationen af blodtrykssænkende lægemiddel og sovemiddel
Du får de parvise kombinationer, der er videnskabeligt undersøgt.
Nej, du skal ikke angive dosis (500mg paracetamol) eller interval (2xdaglig), når du skal søge på et præparat eller indholdsstof. Det er kun selve præparatnavnet eller navnet på indholdsstoffet, du skal skrive. Vælg eventuelt bare navnet fra listen.
Det er desværre sådan, at der indtil videre kun kan søges på indholdsstof, når det gælder naturlægemidler.
Dette sker, når du søger på et kombinationspræparat. Når du søger på et kombinationspræparat, får du præsenteret et resultat for hvert af disse indholdsstoffer.
Indholdet i databasen er resultatet af grundige vurderinger af videnskabelige artikler og konklusioner fra humane forsøg. Hvis du kun får én interaktion på trods af, at du har indtastet flere præparater eller indholdsstoffer, skyldes det, at der endnu ikke er beskrevet (eller fundet) interaktioner af de andre indholdsstoffer i den videnskabelige litteratur.
På Lægemiddelstyrelsens hjemmeside, og i månedsbladet Rationel Farmakoterapi, juni 2015.
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Lægemiddelstyrelsen
Axel Heides Gade 1
2300 København S
Tlf.nr 44 88 95 95
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Interaktionsoplysninger
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1. Paracetamol "Accord" - (ingen præparater og/eller indholdsstoffer matchede dette søgeord!) |
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Interaktionsoplysninger for paracetamol og phenprocoumon |
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Kontrol af koagulationsfaktorer (INR) ved indledning og afslutning af kombinationsbehandlingen.
Kontinuerlig behandling med paracetamol 2-3 gram har ikke resulteret i statistisk signifikante ændringer i INR i kliniske studier. Variation på individniveau er betydelig og de kliniske studier er metodologisk svagere end de tilsvarende for paracetamol og warfarin. Med baggrund i den betydelige interindividuelle variation anbefales kontrol af INR ved samtiddig behandling.
Paracetamol påvirker dog ikke trombocytfunktionen, og kombinationen er mere sikker end kombination af phenprocoumon og NSAID.
mulig
dokumenteret
vitamin K antagonister, perorale phenprocoumon, warfarin paracetamol paracetamol
Paracetamol kan ved regelmæssig indtagelse af mere end 2 gram daglig i mere end 4 dage øge effekten af warfarin, hvorfor patienternes INR bør kontrolleres ved indledning og ophør af behandlingen. Der er ikke fundet yderligere referencer omhandlende interaktion mellem phenprocoumon og paracetamol, idet interaktionen er ringere dokumenteret end for warfarin og ikke er undersøgt ved høje doser på 4 gram paracetamol. Ved kombination med 2-3 gram paracetamol daglig fandt man en lille og ikke klinisk relevant stigning i INR. Interaktioner for warfarin formodes dog også at gælde for phenprocoumon.
Litteraturgennemgang - Vis
Warfarin og paracetamol Prospektive undersøgelser 2 studier (Antlitz AM og Awalt LF, 1969a; Kwan D, Bartle WR et al, 1999) viste ingen effekt på prothrombintiden i henholdsvis 20 patienter i warfarin behandling, som fik 1300 mg paracetamol daglig i 3 dage og 20 raske frivillige, som fik 4 gram paracetamol i 22 dage og et enkelt warfarin dosis dag 0,1 og 22. I modsætning hertil tyder 5 randomiserede kontrollerede på en interaktion. 2 ældre studier med patienter i warfarin behandling viste en moderat (omkring 20%) øgning i prothombin tid ved 2-3 g paracetamol daglig i 2-3 uger, Antlitz AM, Mead JA et al, 1968b; Boeijinga JJ, Boerstra EE et al, 1982. Et randomiseret cross-over studie (Mahe I, Bertrand N et al, 2006) viste ved indgift af 4 gram paracetamol daglig i 14 dage hos 11 patienter i behandling med warfarin en gennemsnitlig stigning i patienternes INR-værdier på 1,04 (SD 0,55) med paracetamol versus 0,20 (SD 0,32) med placebo, og den gennemsnitlige maksimale INR var 3,47 med paracetamol versus 2,61 for placebo. Den signifikante stigning i INR indtrådte allerede efter 4 dages kombinationsbehandling. En begrænsning i dette studie er dog de manglende serumværdier for warfarin og paracetamol. Et studie (Mahe I, Bertrand N et al, 2006) med 20 patienter i warfarin behandling randomiseret til paracetamol 1g fire gange daglig eller placebo i 14 dage viste stigninger i INR-værdier på 1,20 (SD 0,62) med paracetamol versus 0,37 (SD 0,48) med placebo. Den gennemsnitlige maksimale INR var 3,45 for paracetamol versus 2,66 for placebo. Den signifikante stigning i INR indtrådte efter 7 dages kombinationsbehandling. Sideløbende med stigning i INR ved behandling med paracetamol blev der observeret en reduktion af de vitamin K-afhængige koagulationssfaktorer II, VII, IX og X. Dette skyldes sandsynligvis, at N-acetyl-p-benzoquinon-imin,den toksiske metabolit af paracetamol hæmmer enzymerne, som deltager i syntesen af koagulationsfaktorerne, Thijssen HH, Soute BA et al, 2004. 36 patienter i stabil warfarinbehandling blev randomiseret til henholdsvis paracetamol 1gram 2 gange daglig, 1 gram 4 gange daglig eller placebo i fire uger,Parra D, Beckey NP et al, 2007. Efter 2 uger havde gruppen behandlet med 2 g paracetamol signifikant højere INR end placebogruppen. Ved 1,2 og 3 ugers behandling havde gruppen med 4 g paracetamol signifikant højere INR end placebogruppen. Stigningen i INR var på ca. 0,7. INR stigninger med mere en 0,3 over det terapeutiske niveau forekom signifikant hyppigere med paracetamol end med placebo. 45 patienter i behandling med warfarin 2-9 mg/d > 30 dage og med INR 2-3 deltog i et prospektivt, randomiseret og placebo kontrolleret studie (Zhang Q, Bal-dit-Sollier C et al, 2011), hvor der blev tillagt 2 eller 3 g/d af paracetamol eller placebo i 10 dage. Den gennemsnitlige maksimale stigning i INR var hhv. 0.7 ± 0.5 og 0.67 ± 0.62 i patienter der fik hhv. 2 og 3 g/d af paracetamol. INR stigningen var signifikant efter 3 dage og var korreleret med ændring i plasma koncentrationen for paracetamol, faktor II og VII. Retrospektive studier og kasuistikker Et case-control studie med patienter i warfarin behandling, viste en 3,5-10 gange øget risiko for INR større end 6, såfremt patient var i samtidig behandling med paracetamol. Risikoen var dosisafhængig, Hylek EM, Heiman H et al, 1998. I et post-mortem database studie med 328 warfarin brugere var forekomsten af fatale blødninger 4,6 gange større ved samtidig behandling med warfarin og paracetamol end ved behandling kun med paracetamol og 2,7 gange større end ved behandling kun med warfarin. Dette er statistisk signifikant, men konfidensintervaller er ikke beregnet i artiklen, Launiainen T, Sajantila A et al, 2009. Der er 6 kasuistikker, som beskriver stigning i INR eller blødning ved samtidig behandling med warfarin og paracetamol, Bartle WR og Blakely JA, 1991; Bagheri H, Bernhard NB et al, 1999; Andrews FJ, 2002; Ornetti P, Ciappuccini R et al, 2005; Bauer KM, Harenberg J et al, 2005 og Dharmarajan L og Sajjad W, 2007aDharmarajan L og Sajjad W, 2007a. Hos en patient (Gebauer MG, Nyfort-Hansen K et al, 2003i) i behandling med warfarin og 4 gram paracetamol daglig i 3 dage konstateres stigning i patientens INR fra 2,3 til 6,4 og et fald i aktiviteten af koagulationsfaktor VII med ca. 50%. Patientens warfarin plasma-koncentration forblev næsten uændret på trods af stigning i INR til 6,4, hvorfor der muligvis kan være tale om en dynamisk interaktion mellem warfarin og paracetamol. Mekanisme: Ikke endelig etableret. N-acetyl-p-benzoquinon-imin, paracetamols toksiske metabolit, hæmmer formentlig enzymerne, som deltager i syntesen af de vitamin K-afhængige koagulationssfaktorer. Phenprocoumon og paracetamol I et randomiseret kontrolleret studie med 31 patienter i phenprocoumon behandling fik 10 patienter placebo, 11 patienter 1500 mg paracetamol daglig og 10 patienter 3 gram paracetamol daglig i 14 dage, Gadisseur AP, Van Der Meer FJ et al, 2003. Der var ingen statistisk signifikant forskel mellem INR i de tre grupper på noget tidspunkt i forløbet. På 8. dagen var den gennemsnitlige absolutte stigning i INR i behandlingsgrupperne (uanset parecetamoldosis) på 0.45, hvilket blev vurderet til ikke at være klinisk relevant. I et retrospektiv naturalistisk studie med patienter i acenocoumarol og phenprocoumon behandling blev forskellen i INR før og efter paracetamol behandling (n=54) og før og efter benzodiazepin behandling sammenlignet (n=20),van den Bemt PM, Geven LM et al, 2002. Den gennemsnitlige paracetamol dosis var 2,1 gram daglig. Der var ingen signifikant forskel mellem de 2 grupper, men stigning i INR over det terapeutiske niveau forekom hos 6 patienter i paracetamol gruppen versus 0 i benzodiazepingruppen. For de 6 patienter, der fik phenprocoumon og paracetamol, var der en ikke-signifikant tendens til stigning i INR, men variationen var stor. I et kohorte studie blev 54 patienter i behandling med phenprocoumonbehandling og paracetamol sammenlignet med 180, som kun var i behandling med phenprocoumon, Fattinger K, Frisullo R et al, 2002. Den mediane behandlingstid med paracetamol var 5 dage, og den gennemsnitlige dosis 2 gram daglig. Der var ingen signifikant forskel i INR mellem de to grupper (-0.3, 99% CI -0.6,0.1). Supplerende litteratur:Mahe I, Caulin C et al, 2004; Harder S og Thurmann P, 1996; Shek KL, Chan LN et al, 1999; Beyan E, Beyan C et al, 2010
Antlitz AM;Awalt LF, Curr Ther Res Clin Exp, 1969, a, 11:360-361; A double blind study of acetaminophen used in conjunction with oral anticoagulant therapy Acetaminophen, N-acetyl-p-aminophenol, is a frequently used analgesic and antipyretic agent. In a previous study utilizing the maximum recommended dose of acetaminophen (650 mg q.i.d) over a two-week period, some potentiation of oral anticoagulants was indicated. The present study was designed to evaluate the immediate effect of acetaminophen on the prothrombin time in patients receiving oral anticoagulant therapy. Hylek EM;Heiman H;Skates SJ;Sheehan MA;Singer DE, JAMA, 1998, 279:657-662; Acetaminophen and other risk factors for excessive warfarin anticoagulation CONTEXT: Warfarin is highly effective in preventing thromboembolism, but increases the risk of hemorrhage, particularly at an international normalized ratio (INR) greater than 4.0. Identifying causes of excessive anticoagulation in clinical practice could help target patients at risk for elevated INRs. OBJECTIVE: To determine causes of INRs greater than 6.0 in a clinical practice setting. DESIGN: Case- control study. SETTING: Outpatient anticoagulant therapy unit. PATIENTS: Outpatients followed up prospectively from April 1995 to March 1996 who had been taking warfarin for more than 1 month, had a target INR of 2.0 to 3.0, and were able to be interviewed within 24 hours of their reported INR. Case patients had INRs greater than 6.0; controls were randomly selected from patients having INRs between 1.7 and 3.3. MAIN OUTCOME MEASURES: Factors associated with INRs greater than 6.0, including medication use, recent diet, illness, alcohol consumption, and actual warfarin use. RESULTS: A total of 93 cases and 196 controls were interviewed; they did not differ in age, indication for warfarin, length of therapy, warfarin dose, number of prescription medications, or previous INR or long-term INR variability. Acetaminophen ingestion was independently associated in a dose- dependent manner with having an INR greater than 6.0 (P for trend <.001). For the highest-dose category of acetaminophen intake, 9100 mg/wk or more, the odds of having an INR greater than 6.0 were increased 10-fold (95% confidence interval [CI], 2.6-37.9). Other factors independently associated with an INR greater than 6.0 were new medication known to potentiate warfarin (odds ratio [OR], 8.5; 95% CI, 2.9-24.7), advanced malignancy (OR, 16.4; 95% CI, 2.4-111.0), recent diarrheal illness (OR, 3.5; 95% CI,1.4-8.6), decreased oral intake (OR, 3.6; 95% CI, 1.3-9.7), and taking more warfarin than prescribed (OR, 8.1; 95% CI, 2.2-30.0). Higher vitamin K intake (OR, 0.7; 95% CI, 0.5- 0.9) and habitual alcohol consumption of from 1 drink every other day to 2 drinks a day (OR, 0.2; 95% CI, 0.1-0.7) were associated with decreased risk. CONCLUSIONS: These data suggest that acetaminophen is an underrecognized cause of overanticoagulation in the outpatient setting. Several other clinically important risk factors were identified. Increased monitoring of INR values when such risk factors are present or modification of the risk factors themselves should reduce the frequency of dangerously high levels of anticoagulation Launiainen T;Sajantila A;Rasanen I;Vuori E;Ojanpera I, Eur J Clin Pharmacol, 2009; Adverse interaction of warfarin and paracetamol: evidence from a post-mortem study PURPOSE: The aim of the study was to establish the prevalence and nature of potential adverse drug combinations of warfarin in a large post-mortem toxicology database. The concomitant use of warfarin and non-steroidal anti-inflammatory drugs (NSAIDs) was of interest as these drugs have been associated with internal bleeding both in clinical and post-mortem study settings. Another purpose was to obtain facts related to the questioned safety of warfarin-paracetamol and warfarin-tramadol combinations. METHODS: The post-mortem database was searched for a 1-year period. All warfarin-positive cases and cases containing interacting drugs, as defined by the SFINX interaction database (Swedish, Finnish, Interaction X-referencing), were included. For controls, all cases containing paracetamol or tramadol were also included, and for each warfarin-positive case, an age-, sex- and alcohol-matched control case was sourced. The contribution of anticoagulant use to the deaths was evaluated from the death certificates based on medico-legal autopsies. RESULTS: In 33% of the 328 warfarin-positive cases, at least one interacting drug was present, and paracetamol was the most abundant, accounting for 49% (n = 53). When paracetamol and warfarin were detected simultaneously, the number of fatal bleeds was 4.6 and 2.7 times higher compared to paracetamol or warfarin use alone respectively. The presence of an NSAID in combination with warfarin was rare, as only six cases were identified. A majority (66%) of the post-mortem blood samples had a warfarin concentration below 0.5 mg/l, and for the rest of the cases, the mean concentration was 0.70 mg/l. CONCLUSIONS: This study supports the clinical evidence suggesting that warfarin-paracetamol interactions may create significant life-threatening conditions. It also accentuates the significant role post-mortem database research can have in improving drug safety Harder S;Thurmann P, Clin Pharmacokinet, 1996, 30:416-444; Clinically important drug interactions with anticoagulants. An update Coumarin derivatives combine 3 unfavorable properties which make them prone to potentially life threatening drug-drug interactions: (i) high protein binding; (ii) cytochrome P450 dependent metabolism; and (iii) a narrow therapeutic range. An entire list of drugs which are supposed to interact with coumarins (mostly with warfarin) comprises about 250 different compounds. Noteworthy are the interactions with cardiovascular or antilipidaemic drugs which are often coadministered with coumarins: amiodarone, propafenone and fibrates. Cardiovascular drugs which are obviously devoid or proven to be devoid of an interaction are angiotensin converting enzyme (ACE) inhibitors, calcium antagonists, beta-blockers and cardiac glycosides. There are several other drugs which enhance the hypoprothrombinaemic response to coumarins by various mechanisms: inhibitors of the elimination of the eutomer S-(-)-warfarin (e.g. miconazole, phenylbutazone), combined with protein binding displacement (e.g., sulfinpyrazone, phenylbutazone), synergistic hypoprothrombinaemia (e.g. cefazoline). Furthermore, bleeding complications may occur with drugs affecting platelet function [aspirin (acetylsalicylic acid) and several nonsteroidal anti- inflammatories (NSAIDs)]. Strong inducers of coumarin metabolism are rifampicin (rifampin) and carbamazepine. Biphasic interactions may occur where a drug first enhances the hypoprothrombinaemic response to a coumarin but has a sustained inducing effect on coumarin metabolism (e.g. phenytoin or sulfinpyrazone). The complex response of coumarins to concomitant drug therapy makes it difficult to predict the occurrence and degree of a deterioration of anticoagulant control in individual patients. For clinical practice, it seems advisable that one should monitor for changes in prothrombin time when adding or deleting any newly approved drug or any drug suspected (e.g. on the basis of this review) to cause an interaction to patients on coumarin therapy. The onset of the adverse prothrombin time response might be from between 1 to 2 days up to 3 weeks (in case of phenprocoumon) after starting a concomitant drug regimen. With amiodarone, an adverse prothrombin time response might occur up to 2 months after initiating therapy. For heparins, only a drug interaction with aspirin or nitroglycerin seems clinically relevant due to the possibility of coadministration during acute cardiac events. Both drugs are shown to enhance the activated partial thromboplastin time response to heparin Mahe I;Caulin C;Bergmann JF, Drug Saf, 2004, 27:325-333; Does paracetamol potentiate the effects of oral anticoagulants?: a literature review Paracetamol (acetaminophen) is the analgesic and antipyretic therapy of choice for patients receiving oral anticoagulation. It is widely used by patients in both prescription and over-the-counter products, resulting in frequent co-prescription with oral anticoagulants, especially in elderly patients. Indeed, older patients are the most likely to receive this combination of drugs because indications for both oral anticoagulation and analgesic therapy increase with age. For many years reports have presented evidence both for and against the idea that paracetamol may potentiate the anticoagulant effect of oral anticoagulants, thus increasing haemorrhagic risk in patients receiving this combination of drugs. This issue has continued to be a matter of debate in recent publications. No clear practical conclusion can be drawn from the studies because of methodological bias and the lack of clinical relevance. No prospective, randomised study assessing the effect of paracetamol on the anticoagulant effect of oral anticoagulants as used in clinical practice (i.e. the types of patients and dosages used in clinical practice) are available in the literature. The implications are considerable since on the one hand, the ingestion of paracetamol may be a cause of altered anticoagulation in patients who regularly take oral anticoagulation and who may have a haemorrhagic risk factor; and on the other hand, paracetamol might be the analgesic drug of choice that can be used without the need for any restrictions in patients receiving oral anticoagulant drugs. A comprehensive search of Medline and EMBASE for studies and case reports from 1966-2002 was performed in order to review the available literature on the interaction between paracetamol and oral anticoagulant drugs. In conclusion, the potential interaction between oral anticoagulant drugs and paracetamol is an important unanswered question, due to the growing incidence of the concomitant use of these drugs and the possible bleeding implications. The association between paracetamol and the occurrence of excessive INR values remains controversial due to lack of prospective clinical studies assessing the effect of the prescription of paracetamol in patients receiving long-term oral anticoagulation in clinical conditions. Such a study is currently ongoing Bauer KM;Harenberg J;Jorg I;Diezler P;Reinshagen K;Burkhardt H;Gladisch R, Internist (Berl), 2005, 46:1394-1398; Dysphagie nach Einnahme einer Paracetamoltablette unter oraler Antikoagulation. [Dysphagia after taking an acetaminophen-tablet during oral anticoagulation] The bezoar is only one example for an urgent indication for endoscopic intervention during oral anticoagulation. Because of the lack of life-threatening indication the endoscopy often is delayed for 1 to 3 days until the International Normalized Ratio (INR) is nearly in normal range. As well as the application of unique guidelines on endoscopy during oral anticoagulation new future oral anticoagulants with lower half-life may help to shorten suffering of patients Boeijinga JJ;Boerstra EE;Ris P;Breimer DD;Jeletich-Bastiaanse A, Lancet, 1982, 1:506; Interaction between paracetamol and coumarin anticoagulants Prospektivt studie omhandlende 20 patienter i behandling med coumarinderivater. Ved kombinationsbehandling med paracetamol sås signifikant stigninger i patienternes PT. Ornetti P;Ciappuccini R;Tavernier C;Maillefert JF, Rheumatology (Oxford), 2005, 44:1584-1585; Interaction between paracetamol and oral anticoagulants Mahe I;Bertrand N;Drouet L;Bal Dit Sollier C;Simoneau G;Mazoyer E;Caulin C;Bergmann JF, Haematologica, 2006, 91:1621-1627; Interaction between paracetamol and warfarin in patients: a double-blind, placebo-controlled, randomized study BACKGROUND AND OBJECTIVES: Paracetamol (acetaminophen) has occasionally been reported to interact with warfarin. The primary end-point of this study was to investigate whether paracetamol initiation potentiates the anticoagulant effect of warfarin and the mechanism of the interaction. DESIGN AND METHODS: In a double-blind placebo-controlled, randomized, cross-over study, 20 patients on stable oral anticoagulant therapy with warfarin for at least 1 month were randomized to receive placebo or paracetamol 1g four times daily for 14 days. International Normalized Ratio (INR) and clotting factors activities were measured before the first administration and then on days 2, 4, 7, 9, 11,14. RESULTS: Mean INR rose rapidly after the start of paracetamol and was significantly increased within one week of paracetamol intake compared to placebo, p=0.0002. The INR values reached a mean maximum of 3.45+/-0.78 with paracetamol versus 2.66+/-0.73 with placebo (p=0.03), corresponding to a maximum increase from baseline of 1.20+/-0.62 with paracetamol versus 0.37+/-0.48 with placebo (p<0.001). Together with the rise in INR on paracetamol treatment there were significant reductions in the vitamin K-dependent clotting factors II, VII, IX and X. INTERPRETATION AND CONCLUSIONS: The most plausible hypothesis to explain the in vivo interaction is that paracetamol (or its metabolites) interfere with enzymes involved in vitamin K-dependent coagulation factor synthesis. Paracetamol at 4 g daily (a dose higher than that used in clinical practice) potentiates the anticoagulant response produced by warfarin. Clinicians should be aware of this clinically significant and underestimated interaction Beyan E;Beyan C;Acar VS, Tomt indhold, 2010, 66:217-218; Letter to the editor: Adverse interaction of warfarin and paracetamol: Evidence from a post-mortem study Fattinger K;Frisullo R;Masche U;Braunschweig S;Meier PJ;Roos M, Eur J Clin Pharmacol, 2002, 57:863-867; No clinically relevant drug interaction between paracetamol and phenprocoumon based on a pharmacoepidemiological cohort study in medical inpatients OBJECTIVE: A recent case control study suggests that paracetamol at a dosage above 1300 mg/day increases the anticoagulant effects of warfarin. In many European countries, phenprocoumon and not warfarin is used as an anticoagulant. However, the effects of paracetamol on the anticoagulant effects of phenprocoumon have so far not been evaluated. METHODS: This study is based on the data recorded prospectively between 1996 and 1998 in two Swiss teaching hospitals in the pharmacoepidemiological database of the SAS/CHDM project. As a first step, all phenprocoumon-treated patients with at least one international normalized ratio (INR) determination at least 4 days after cohort entry were selected and evaluated concerning paracetamol co-administration. The 'paracetamol group' included only patients receiving at least 1300 mg/day paracetamol on the 3 days preceding the INR determination, whereas the comparison group contained only patients without paracetamol exposure during hospital stay. Thereafter, INR values of the paracetamol and the comparison groups were compared. RESULTS: The paracetamol and the comparison groups included 54 and 180 patients, respectively. Patients' characteristics in both groups were comparable. Patients in the paracetamol group received on average 2220 +/- 651 mg/day paracetamol. The median duration of paracetamol exposure was 5 days. The median difference in INR values between the paracetamol and the comparison groups was -0.3 (with a 99% confidence interval of -0.6, 0.1). CONCLUSIONS: These results suggest that paracetamol co-administration at a dosage of 2000-2500 mg/day for 3 days has no clinically relevant effects on the anticoagulant effects of phenprocoumon Thijssen HH;Soute BA;Vervoort LM;Claessens JG, Thromb Haemost, 2004, 92:797-802; Paracetamol (acetaminophen) warfarin interaction: NAPQI, the toxic metabolite of paracetamol, is an inhibitor of enzymes in the vitamin K cycle Paracetamol (acetaminophen) is generally considered to be the analgesic of choice for patients undergoing oral anticoagulant therapy. Occasionally, however, interactions have been reported with therapeutic doses of the analgesic, e.g. if the drug is taken for a longer period of time. The mechanism of this interaction is not clearly understood. We investigated the effects of paracetamol and its toxic metabolite N-acetyl-para-benzoquinoneimine (NAPQI) on in vitro vitamin K-dependent gamma-carboxylase (VKD-carb) and vitamin K epoxide reductase (VKOR) activities. Paracetamol had no effect in either enzymatic reactions. NAPQI, on the other hand, appeared to interfere with VKD carb activity via two mechanisms; 1) oxidation of the cofactor vitamin K-hydroquinone, 2) inactivation of the enzyme. The inactivation, in micromolar ranges, is not reversible and may be the result of covalent binding of NAPQI with functional amino acids. NAPQI also inhibited VKOR, but at higher concentrations. Unexpectedly, N-acetylcysteine was found to inhibit VKOR activity at concentrations that are obtained during rescue therapy of paracetamol intoxication. We conclude that, the potentiation of the oral anticoagulant effect by paracetamol is likely to result from NAPQI-induced inhibition of enzymes of the vitamin K cycle, particularly VKD-carb Mahe I;Bertrand N;Drouet L;Simoneau G;Mazoyer E;Bal-Dit SC;Caulin C;Bergmann JF, Br J Clin Pharmacol, 2005, 29:371-374; Paracetamol: A haemorrhagic risk factor in patients on warfarin Aim: To quantify the effect of paracetamol on the anticoagulant effect of warfarin under normal clinical conditions. Patients and methods: In a prospective double-blind, cross-over, placebo-controlled study, 11 patients on stable warfarin therapy received in random order two 14-day regimens of paracetamol 4 g day<sup>-1</sup> or placebo, with a 14-day or more wash-out period in between, time necessary to fulfil the inclusion criteria. Results: In patients on paracetamol, the mean maximum increase in the International Normalized Ratio (INR) observed was 1.04 ± 0.55 vs. 0.20 ± 0.32 in those on placebo (P = 0.003). The mean maximum INR observed was significantly higher with paracetamol than with placebo (3.47 vs. 2.61, P = 0.01). In patients receiving paracetamol, the mean observed INR was significantly increased after 4 days (+0.6 ± 0.6, P < 0.001). Conclusion: Paracetamol at 4 g day<sup>-1</sup> induces a significant increase in INR in patients receiving a stable regimen of warfarin, increasing the risk of bleeding associated with warfarin. < copyright > 2004 Blackwell Publishing Ltd Dharmarajan L;Sajjad W, J Am Med Dir Assoc, 2007, a, 8:545-547; Potentially lethal acetaminophen-warfarin interaction in an older adult: an under-recognized phenomenon? Antlitz AM;Mead JA;Tolentino MA, Curr Ther Res Clin Exp, 1968, b, 10:501-507; Potentiation of oral anticoagulant therapy by acetaminophen Physicians frequently advise oral anticoagulant drugs following myocardial infarction, pulmonary infarction, some forms of cerebral vascular occlusion, and other thromboelic syndromes. The management of concurrent disease often requires the administration of other drugs during the period of anticoagulation. A thorough knowledge of drug interactions with the oral anticoagulants is necessary to maintain the relatively narrow range of safe and effective dosage.Paracetamol has been recommended for the use as an analgesic in anticoagulated patients because of its alleged lack of effect on anticoagulation. This study was undertaken to evaluate the effect of paracetamol on the prothrombin time and on the anticoagulant requirements of a group of patients receiving long-term anticoagulation therapy. Bagheri H;Bernhard NB;Montastruc JL, Ann Pharmacother, 1999, 33:506; Potentiation of the acenocoumarol anticoagulant effect by acetaminophen Patient i kombinationsbehandling med warfarin og paracetamol. Efter ophør med paracetamol behandlingen falder patientens INR med ca. 55%.Ved start på paracetamol behandlingen igen stiger patientens INR atter. Bartle WR;Blakely JA, JAMA, 1991, 265:1260; Potentiation of warfarin anticoagulation by acetaminophen Kasuistik omhandlende en patient der indlægges på hospital pga. hæmaturi og gingivale blødninger. Usikkert hvor store doser paracetamol og kodein patienten har indtaget. PT stærkt forøget. Andrews FJ, Emerg Med J, 2002, 19:84-85; Retroperitoneal haematoma after paracetamol increased anticoagulation Drugs containing paracetamol are widely used as analgesics but may result in increased anticoagulation in patients who take warfarin, the mechanism being unclear. Retroperitoneal haemorrhage is a serious and well described complication in patients who develop increased anticoagulation; this may result in a femoral neuropathy. Both conservative and surgical treatments have been advocated for this complication Gadisseur AP;Van Der Meer FJ;Rosendaal FR, J Thromb Haemost, 2003, 1:714-717; Sustained intake of paracetamol (acetaminophen) during oral anticoagulant therapy with coumarins does not cause clinically important INR changes: a randomized double-blind clinical trial Paracetamol (acetaminophen) is routinely advised when non-steroidal anti-inflammatory drugs (NSAID) are necessary during oral anticoagulant treatment (OAT) because it has no relevant effect on the primary hemostasis. However, in a recent case-control study a dose-related effect was observed of paracetamol intake on the International Normalized Ratio (INR) values making its use controversial during OAT. Our objectives were to determine the effect of paracetamol on the INR values during OAT independent of underlying illness. A double-blind randomized controlled trial in which 31 out-patients on coumarin oral anticoagulant therapy with phenprocoumon, aged 18-70 years, with a planned treatment duration of more than 12 weeks, and an INR target range of 2.5-3.5, were included. Patients were randomized for placebo (10 patients), paracetamol 1500 mg daily (11 patients) or paracetamol 3000 mg daily (10 patients) for 14 days during the stable phase of coumarin OAT and INR values at day 1, 8, 15, 22 and 29 were measured. At day 8 a mean rise of 0.46 INR was seen in both paracetamol groups compared to placebo. At day 15 there was no difference between placebo and paracetamol 1500 mg daily, and a small mean rise of 0.22 INR in the paracetamol 3000 mg daily group. The sustained use of paracetamol (acetaminophen) during oral anticoagulant therapy in itself does not provoke clinically relevant INR changes. Any important INR rise will predominantly be the result of the illness necessitating the intake of this medication. A difference has to be made between those patients taking paracetamol (acetaminophen) for pain relief or as an antipyretic during infectious diseases Parra D;Beckey NP;Stevens GR, Pharmacotherapy, 2007, 27:675-683; The effect of acetaminophen on the international normalized ratio in patients stabilized on warfarin therapy STUDY OBJECTIVE: To determine whether an interaction exists between acetaminophen and warfarin that alters the international normalized ratio (INR). DESIGN: Prospective, randomized, double-blind, placebo-controlled trial. SETTING: Anticoagulation clinic at a Veterans Affairs Medical Center. PATIENTS: Thirty-six adult patients receiving warfarin with stable INRs, defined as two consecutive INRs at least 3 weeks apart that were within the therapeutic range. INTERVENTION: Patients were randomly assigned to receive acetaminophen 1 g twice/day along with matching placebo twice/day (12 patients), acetaminophen 1 g 4 times/day (12 patients), or matching placebo 4 times/day (12 patients) for 4 weeks. MEASUREMENTS AND MAIN RESULTS: The primary end point was the difference in mean INR between groups at weekly intervals. Secondary end points were the percentages of patients in each group with supratherapeutic (INR > or = 0.3 above the upper limit of their therapeutic range) or subtherapeutic (INR > or = 0.2 or 0.3 below the lower limit of their respective therapeutic range of 2.0-3.0 or 2.5-3.5) INRs, and the difference in mean serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels between groups at biweekly intervals. Slow enrollment and a preliminary observation that 15 patients experienced an elevated INR prompted early termination of the study. At week 2, the group receiving acetaminophen 2 g/day had a significantly higher mean INR versus the placebo group (p=0.01). At weeks 1, 2, and 3, the acetaminophen 4-g/day group had significantly higher mean INRs compared with those in the placebo group (p=0.04, p=0.01, p=0.01, respectively). In addition, 13 (54%) of 24 patients in the acetaminophen groups combined exceeded the upper limit of their therapeutic range by 0.3 or greater compared with only 2 (17%) of 12 patients in the placebo group. No statistically significant differences in serum ALT or AST levels between either acetaminophen group versus the placebo group were found at week 4; however, there was a statistically significant increase in mean ALT level at week 2 in the acetaminophen 4-g/day group versus the placebo group. CONCLUSION: These findings support the existence of a clinically significant interaction between warfarin and daily use of acetaminophen 2-4 g, necessitating close monitoring of patients who receive this drug combination. Whether this interaction occurs when acetaminophen is taken in lower doses or is used sporadically requires further study Kwan D;Bartle WR;Walker SE, J Clin Pharmacol, 1999, 39:68-75; The effects of acetaminophen on pharmacokinetics and pharmacodynamics of warfarin The oral anticoagulant warfarin is clinically administered as a racemic mixture of two enantiomers, (R) and (S). Many relevant drug interactions with warfarin have been attributed to the specific metabolic inhibition of the elimination of the more pharmacologically active (S)-enantiomer. To investigate reports that acetaminophen can potentiate the anticoagulant effect of warfarin, 20 healthy male volunteers were each given single oral 20 mg doses of racemic warfarin on three separate occasions: (1) alone, (2) after 1 day of acetaminophen (4 g/d), and (3) after 2 weeks of acetaminophen (4 g/d). The urinary excretion pattern of acetaminophen and its metabolites was not significantly altered over its course of administration. The (R)- and (S)-enantiomers of warfarin exhibited significantly different pharmacokinetic properties. However, acetaminophen did not alter the disposition of either (R)- or (S)-warfarin. All subjects exhibited a pharmacodynamic response to racemic warfarin. The response was not significantly altered in the presence of acute or chronic acetaminophen dosing, as assessed by prothrombin time and factor VII concentrations van den Bemt PM;Geven LM;Kuitert NA;Risselada A;Brouwers JR, Tomt indhold, 2002, 24:201-204; The potential interaction between oral anticoagulants and acetaminophen in everyday practice OBJECTIVE: The drug-drug interaction between oral anticoagulants (especially warfarin) and acetaminophen has been described, but evidence is conflicting and evidence for a similar interaction between acenocoumarol or phenprocoumon and acetaminophen is limited. Therefore, a study was performed to determine the influence of acetaminophen on oral anticoagulation with acenocoumarol or phenprocoumon in everyday practice. METHOD: Included were patients from two Dutch anticoagulant clinics who had used oral anticoagulants for at least three months and who started with acetaminophen (case group) or benzodiazepines (control group). RESULTS: Fifty-four patients were included who had a first prescription of acetaminophen in their pharmacy record (during oral anticoagulant use) and twenty patients with a first prescription of a benzodiazepine (during oral anticoagulant use). The INR (International Normalized Ratio) difference before and after acetaminophen use was not statistically significant between the two groups and showed no dose dependency. CONCLUSION: These data do not demonstrate that acetaminophen, in the dosages used in everyday practice, has a clinically relevant influence on the INR in patients using acenocoumarol or phenprocoumon Gebauer MG;Nyfort-Hansen K;Henschke PJ;Gallus AS, Pharmacotherapy, 2003, 23:109-112; Warfarin and acetaminophen interaction A 74-year-old man who was receiving warfarin for atrial fibrillation experienced an abrupt increase in his international normalized ratio (INR) after taking acetaminophen. To investigate this effect, the patient's anticoagulation therapy was stabilized, and he was given acetaminophen 1 g 4 times/day for 3 days. His INR rose from 2.3 before receiving acetaminophen to 6.4 on the day after acetaminophen was discontinued. Warfarin was stopped for 2 days, and the patient's INR returned to 2.0. Warfarin was restarted at the same dosage, and his INR remained within 2.0-3.0 for 6 months. Factor VII activity decreased from 29.4% before acetaminophen therapy to 15.5% when his INR was 6.4, and factor X activity fell from 27.0% to 20.2%. His warfarin plasma concentration was 1.54 microg/ml before acetaminophen compared with 1.34 microg/ml when his INR was 6.4. No significant changes in drug intake, clinical status, diet, or lifestyle were noted. Changes in INR of this magnitude with the addition of another drug during stable anticoagulation therapy suggest a drug interaction. The lack of an increase in warfarin plasma concentration associated with the increased INR suggests a possible pharmacodynamic mechanism for this interaction. Acetaminophen or a metabolite may enhance the effect of oral coumarin anticoagulants by augmenting vitamin K antagonism. Thus, the anticoagulant effect of warfarin may be significantly elevated after only a few days of acetaminophen therapy. Patients receiving warfarin should be counseled to have their INR monitored more frequently when starting acetaminophen at dosages exceeding 2 g/day Shek KL;Chan LN;Nutescu E, Pharmacotherapy, 1999, 19:1153-1158; Warfarin-acetaminophen drug interaction revisited Physicians and pharmacists routinely advise patients receiving warfarin to take acetaminophen for pain or fever because of its relative safety; however, a recent study questioned the safety of such practice. A comprehensive search of MEDLINE and IPA for human studies and case reports from 1966-1999 revealed evidence that acetaminophen may potentiate the effect of warfarin by a mechanism that has yet to be elucidated. Due to lack of a safer alternative, acetaminophen still should be the analgesic and antipyretic of choice in patients taking warfarin, as long as excessive amounts and prolonged administration (> 1.3 g acetaminophen/day for > 2 wks) are avoided. With the high degree of interpatient variability and the unpredictability of various drug- drug interactions with warfarin, close and frequent monitoring of international normalized ratios is the key for safe oral anticoagulation therapy
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