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Drug interactions between Coumadin and Tylenol

Results for the following 2 drugs:
Coumadin (warfarin)
Tylenol (acetaminophen)

Interactions between your drugs


warfarin ↔ acetaminophen

Applies to:Coumadin (warfarin) and Tylenol (acetaminophen)

Acetaminophen (APAP) may potentiate the hypoprothrombinemic effect of warfarin and other oral anticoagulants, although data are somewhat conflicting and the mechanism of interaction is unknown. The interaction has generally been associated with prolonged ingestion of relatively high APAP dosages (greater than 1.3 g/day continuously for greater than 1 week) but not with brief, intermittent exposures of average doses. Reported increases in prothrombin time or INR from most studies were often small but statistically significant, although there have been isolated case reports citing bleeding episodes and clinically significant alterations in coagulation parameters. In contrast, one retrospective study found no significant effect of APAP 2000 to 2500 mg/day on the anticoagulant effect of phenprocoumon, and another study reported no effect of APAP 4 g/day for 2 weeks on single-dose warfarin pharmacokinetics and pharmacodynamics in healthy volunteers. Due to the lack of safer alternatives, acetaminophen is considered the analgesic and antipyretic drug of choice for patients receiving oral anticoagulant therapy. However, caution is recommended during concomitant therapy, particularly if high dosages of APAP are used for a prolonged period. Patients should be advised to promptly report any signs of bleeding to their physician, including pain, swelling, headache, dizziness, weakness, prolonged bleeding from cuts, increased menstrual flow, vaginal bleeding, nosebleeds, bleeding of gums from brushing, unusual bleeding or bruising, red or brown urine, or red or black stools.


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  2. Fattinger K, Frisullo R, Masche U, Braunschweig S, Meier PJ, Roos M "No clinically relevant drug interaction between paracetamol and phenprocoumon based on a pharmacoepidemiological cohort study in medical inpatients." Eur J Clin Pharmacol 57 (2002): 863-7
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  5. Shek KL, Chan LN, Nutescu E "Warfarin-acetaminophen drug interaction revisited." Pharmacotherapy 19 (1999): 1153-8
  6. Kwan D, Bartle WR, Walker SE "The effects of acetaminophen on pharmacokinetics and pharmacodynamics of warfarin." J Clin Pharmacol 39 (1999): 68-75
  7. Antlitz AM, Mead JA Jr, Tolentino MA "Potentiation of oral anticoagulant therapy by acetaminophen." Curr Ther Res Clin Exp 10 (1968): 501-7
  8. Boeijinga JJ, Boerstra EE, Ris P, Breimer DD, Jeletich-Bastiaanse A "Interaction between paracetamol and coumarin anticoagulants." Lancet 1 (1982): 506
  9. Bagheri H, Bernhard NB, Montastruc JL "Potentiation of the acenocoumarol anticoagulant effect by acetaminophen." Ann Pharmacother 33 (1999): 506
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  11. Singer DE, Skates SJ "Acetaminophen and risk factors for excess anticoagulation with warfarin." JAMA 281 (1999): 37
View all 11 references

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Drug and food interactions


warfarin food

Applies to: Coumadin (warfarin)

MONITOR: Vitamin K may antagonize the hypoprothrombinemic effect of oral anticoagulants. Vitamin K is a cofactor in the synthesis of blood clotting factors that are inhibited by oral anticoagulants, thus intake of vitamin K through supplements or diet can reverse the action of oral anticoagulants. Resistance to oral anticoagulants has been associated with consumption of foods or enteral feedings high in vitamin K content. Likewise, a reduction of vitamin K intake following stabilization of anticoagulant therapy may result in elevation of the INR and bleeding complications. Foods rich in vitamin K include beef liver, broccoli, Brussels sprouts, cabbage, collard greens, endive, kale, lettuce, mustard greens, parsley, soy beans, spinach, Swiss chard, turnip greens, watercress, and other green leafy vegetables. Moderate to high levels of vitamin K are also found in other foods such as asparagus, avocados, dill pickles, green peas, green tea, canola oil, margarine, mayonnaise, olive oil, and soybean oil. Snack foods containing the fat substitute, olestra, are fortified with 80 mcg of vitamin K per each one ounce serving so as to offset any depletion of vitamin K that may occur due to olestra interference with its absorption. Whether these foods can alter the effect of oral anticoagulants has not been extensively studied. One small study found that moderate consumption (1.5 servings/day) does not significantly affect the INR after one week in patients receiving long-term anticoagulation.

Consumption of large amounts of mango fruit has been associated with enhanced effects of warfarin. The exact mechanism of interaction is unknown but may be related to the vitamin A content, which may inhibit metabolism of warfarin. In one report, thirteen patients with an average INR increase of 38% reportedly had consumed one to six mangos daily 2 to 30 days prior to their appointment. The average INR decreased by 17.7% after discontinuation of mango ingestion for 2 weeks. Rechallenge in two patients appeared to confirm the interaction.

Limited data also suggest a potential interaction between warfarin and cranberry juice resulting in changes in the INR and/or bleeding complications. The mechanism is unknown but may involve alterations in warfarin metabolism induced by flavonoids contained in cranberry juice. At least a dozen reports of suspected interaction have been filed with the Committee on Safety of Medicines in the U.K. since 1999, including one fatality. In the fatal case, the patient's INR increased dramatically (greater than 50) six weeks after he started drinking cranberry juice, and he died from gastrointestinal and pericardial hemorrhage. However, the patient was also taking cephalexin for a chest infection and had not eaten for two weeks prior to hospitalization, which may have been contributing factors. Other cases involved less dramatic increases or instabilities in INR following cranberry juice consumption, and a decrease was reported in one, although details are generally lacking. In a rare published report, a 71-year-old patient developed hemoptysis, hematochezia, and shortness of breath two weeks after he started drinking 24 ounces of cranberry juice a day. Laboratory test results on admission revealed a decrease in hemoglobin, an INR greater than 18, and prothrombin time exceeding 120 seconds. The patient recovered after warfarin doses were withheld for several days and he was given packed red blood cells, fresh-frozen plasma, and subcutaneous vitamin K. It is not known if variations in the constituents of different brands of cranberry juice may affect the potential for drug interactions.

A patient who was stabilized on warfarin developed a large hematoma in her calf in association with an elevated INR of 14 following consumption of approximately 3 liters of pomegranate juice in the week prior to admission. In vitro data suggest that pomegranate juice can inhibit CYP450 2C9, the isoenzyme responsible for the metabolic clearance of the biologically more active S(-) enantiomer of warfarin. In rats, pomegranate juice has also been shown to inhibit intestinal CYP450 3A4, the isoenzyme that contributes to the metabolism of R(+) warfarin.

Black currant juice and black currant seed oil may theoretically increase the risk of bleeding or bruising if used in combination with anticoagulants. The proposed mechanism is the antiplatelet effects of the gamma-linolenic acid constituent in black currants.

Soy protein in the form of soy milk was thought to be responsible for a case of possible warfarin antagonism in an elderly male stabilized on warfarin. The exact mechanism of interaction is unknown, as soy milk contains only trace amounts of vitamin K. Subtherapeutic INR values were observed approximately 4 weeks after the patient began consuming soy milk daily for the treatment of hypertriglyceridemia. No other changes in diet or medications were noted during this time. The patient's INR returned to normal following discontinuation of the soy milk with no other intervention.

An interaction with chewing tobacco was suspected in a case of warfarin therapy failure in a young male who was treated with up to 25 to 30 mg/day for 4.5 years. The inability to achieve adequate INR values led to eventual discontinuation of the chewing tobacco, which resulted in an INR increase from 1.1 to 2.3 in six days. The authors attributed the interaction to the relatively high vitamin K content in smokeless tobacco.

MANAGEMENT: Intake of vitamin K through supplements or diet should not vary significantly during oral anticoagulant therapy. The diet in general should remain consistent, as other foods containing little or no vitamin K such as mangos and soy milk have been reported to interact with warfarin. Some experts recommend that continuous enteral nutrition should be interrupted for one hour before and one hour after administration of the anticoagulant dose and that enteral formulas containing soy protein should be avoided. Patients should also consider avoiding or limiting the consumption of cranberry juice or other cranberry formulations (e.g., encapsulated dried cranberry powder), pomegranate juice, black currant juice, and black currant seed oil.


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  3. Beckey NP, Korman LB, Parra D "Effect of the moderate consumption of olestra in patients receiving long-term warfarin therapy." Pharmacotherapy 19 (1999): 1075-9
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  7. Walker FB "Myocardial infarction after diet-induced warfarin resistance." Arch Intern Med 144 (1984): 2089-90
  8. Kazmier FJ, Spittell JA Jr "Coumarin drug interactions." Mayo Clin Proc 45 (1970): 249-55
  9. Pedersen FM, Hamberg O, Hess K, Ovesen L "The effect of dietary vitamin K on warfarin-induced anticoagulation." J Intern Med 229 (1991): 517-20
  10. Grant P "Warfarin and cranberry juice: an interaction?" J Heart Valve Dis 13 (2004): 25-6
  11. Griffith LD, Olvey SE, Triplett WC "Increasing prothrombin times in a warfarin-treated patient upon withdrawal of ensure plus." Crit Care Med 10 (1982): 799-800
  12. Wells PS, Holbrook AM, Crowther NR, Hirsh J "Interactions of warfarin with drugs and food." Ann Intern Med 121 (1994): 676-83
  13. Ministerio de Sanidad y Consumo. Gobierno de España "AEMPS. Agencia Española de Medicamentos y Productos Sanitarios. Available from: URL:"
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  15. Zallman JA, Lee DP, Jeffrey PL "Liquid nutrition as a cause of warfarin resistance." Am J Hosp Pharm 38 (1981): 1174
  16. Griffiths AP, Beddall A, Pegler S "Fatal haemopericardium and gastrointestinal haemorrhage due to possible interaction of cranberry juice with warfarin." J R Soc Health 128 (2008): 324-6
  17. Roberts D, Flanagan P "Case report: Cranberry juice and warfarin." Home Healthc Nurse 29 (2011): 92-7
  18. Watson AJ, Pegg M, Green JR "Enteral feeds may antagonise warfarin." Br Med J 288 (1984): 557
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  20. Kuykendall JR, Houle MD, Rhodes RS "Possible warfarin failure due to interaction with smokeless tobacco." Ann Pharmacother 38 (2004): 595-7
  21. Chow WH, Chow TC, Tse TM, Tai YT, Lee WT "Anticoagulation instability with life-threatening complication after dietary modification." Postgrad Med J 66 (1990): 855-7
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  32. Cambria-Kiely JA "Effect of soy milk on warfarin efficacy." Ann Pharmacother 36 (2002): 1893-6
View all 32 references

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Therapeutic duplication warnings

No therapeutic duplications were found for your selected drugs.

Drug Interaction Classification

The classifications below are a guideline only. The relevance of a particular drug interaction to a specific patient is difficult to determine using this tool alone given the large number of variables that may apply.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No information available.

Do not stop taking any medications without consulting your healthcare provider.

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