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      Interacción warfarina y acetaminofén Evaluación para establecer su relevancia clínica Translated title: Warfarin and acetaminophen interaction Assessment to establish its clinical relevance


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          Objetivo: realizar una revisión estructurada de la interacción warfarina y acetaminofén, buscando establecer su relevancia clínica y profundizar en el mecanismo de dicha interacción. Método: revisión estructurada en PubMed/Medline, de artículos en inglés y español, buscando los términos warfarin AND (acetaminophen OR paracetamol) en el título o resumen. La búsqueda se complementó con las referencias de artículos valorados como importantes. Los trabajos se agruparon en: relacionados con el aumento de sangrado por la interacción warfarina-acetaminofén, o relacionados con el mecanismo de la interacción. Resultados: se identificaron 45 artículos, de los cuales se incluyeron 15 en la revisión: 11 relacionados con el aumento del riesgo de sangrado por la interacción y cuatro con el mecanismo de la interacción. La gravedad del efecto (aumento de la probabilidad de sangrado) se consideró moderada; mientras que la probabilidad de aparición fue valorada como definida. Además, se identificó una relación entre la dosis de acetaminofén y el riesgo de sangrado. Por su parte, el N-acetil-para-benzoquinona-imina (metabolito del acetaminofén) inhibe enzimas del ciclo de la vitamina K y tiene un efecto sinérgico con el efecto anticoagulante de la warfarina. Conclusiones: la relevancia clínica de la interacción warfarina - acetaminofén es de riesgo alto, debido a que la gravedad del efecto (aumento del riesgo de sangrado) es moderada y su probabilidad de presentación es definida. Por tanto, estos dos medicamentos pueden ser utilizados conjuntamente, pero se debe realizar una estricta monitorización. El metabolito N-acetil-para-benzoquinona-imina es el responsable del aumento del efecto anticoagulante de la warfarina. (Acta Med Colomb 2013; 38: 22-27)

          Translated abstract

          Objective: to make a structured review of the interaction between warfarin and acetaminophen, seeking to establish its clinical relevance and deepen in the mechanism of this interaction. Method: structured review of PubMed/Medline of articles in English and Spanish, looking warfarin and acetaminophen or paracetamol in the title or abstract. The search was complemented with references of articles rated as important. The papers were grouped in: related to increased bleeding due to warfarin-acetaminophen interaction, or related to the mechanism of the interaction. Results: we identified 45 articles, of which 15 were included in the review: 11 related to increased risk of bleeding due to the interaction and 4 with the mechanism of the interaction. The severity of the effect (increased likelihood of bleeding) was considered moderate, whereas the probability of appearance was rated as definite. In addition, we identified a relationship between the dose of acetaminophen and the risk of bleeding. In turn, the N-acetyl-para-benzoquinone-imine (metabolite of acetaminophen) inhibits enzymes of the vitamin K cycle and has a synergistic effect with the anticoagulant effect of warfarin. Conclusions: the clinical relevance of the interaction warfarin-acetaminophen is of high risk due to the fact that the severity of the effect (increased risk of bleeding) is moderate and the probability of its presentation is definite. Therefore, these two drugs can be used together, but a strict monitoring should be conducted. The metabolite N-acetyl-para-benzoquinone-imine is responsible for the increase in the anticoagulant effect of warfarin. (Acta Med Colomb 2013; 38: 22-27)

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          Acetaminophen (paracetamol) is a selective cyclooxygenase-2 inhibitor in man.

          For more than three decades, acetaminophen (INN, paracetamol) has been claimed to be devoid of significant inhibition of peripheral prostanoids. Meanwhile, attempts to explain its action by inhibition of a central cyclooxygenase (COX)-3 have been rejected. The fact that acetaminophen acts functionally as a selective COX-2 inhibitor led us to investigate the hypothesis of whether it works via preferential COX-2 blockade. Ex vivo COX inhibition and pharmacokinetics of acetaminophen were assessed in 5 volunteers receiving single 1000 mg doses orally. Coagulation-induced thromboxane B(2) and lipopolysaccharide-induced prostaglandin E(2) were measured ex vivo and in vitro in human whole blood as indices of COX-1 and COX-2 activity. In vitro, acetaminophen elicited a 4.4-fold selectivity toward COX-2 inhibition (IC(50)=113.7 micromol/L for COX-1; IC(50)=25.8 micromol/L for COX-2). Following oral administration of the drug, maximal ex vivo inhibitions were 56% (COX-1) and 83% (COX-2). Acetaminophen plasma concentrations remained above the in vitro IC(50) for COX-2 for at least 5 h postadministration. Ex vivo IC(50) values (COX-1: 105.2 micromol/L; COX-2: 26.3 micromol/L) of acetaminophen compared favorably with its in vitro IC(50) values. In contrast to previous concepts, acetaminophen inhibited COX-2 by more than 80%, i.e., to a degree comparable to nonsteroidal antiinflammatory drugs (NSAIDs) and selective COX-2 inhibitors. However, a >95% COX-1 blockade relevant for suppression of platelet function was not achieved. Our data may explain acetaminophen's analgesic and antiinflammatory action as well as its superior overall gastrointestinal safety profile compared with NSAIDs. In view of its substantial COX-2 inhibition, recently defined cardiovascular warnings for use of COX-2 inhibitors should also be considered for acetaminophen.
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            Oral Anticoagulants: Mechanism of Action, Clinical Effectiveness, and Optimal Therapeutic Range

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              Acetaminophen and other risk factors for excessive warfarin anticoagulation.

              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. To determine causes of INRs greater than 6.0 in a clinical practice setting. Case-control study. Outpatient anticoagulant therapy unit. 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. Factors associated with INRs greater than 6.0, including medication use, recent diet, illness, alcohol consumption, and actual warfarin use. 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. 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.

                Author and article information

                Acta Medica Colombiana
                Acta Med Colomb
                Asociacion Colombiana de Medicina Interna (Bogotá, Distrito Capital, Colombia )
                January 2013
                : 38
                : 1
                : 22-25
                [02] orgnameUniversidad de Antioquia orgdiv1Facultad de Química
                [03] Medellín orgnameUniversidad CES orgdiv1Facultad de Medicina
                [01] orgnameUniversidad de Antioquia orgdiv1Universidad CES orgdiv2Facultad de Medicina
                [04] Medellín orgnameUniversidad de Antioquia orgdiv1Facultad de Química Farmacéutica Colombia
                S0120-24482013000100007 S0120-2448(13)03800107

                This work is licensed under a Creative Commons Attribution 4.0 International License.

                : 25 February 2013
                : 26 July 2012
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 34, Pages: 4

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                Self URI: Texto completo solamente en formato PDF (ES)

                clinical evidence,interaction mechanism,drug interaction,acetaminophen,warfarin,evidencia clínica,mecanismo de interacción,interacción medicamentosa,acetaminofén,warfarina


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