Alcohol and Warfarin, When Simplicity is More Complex than Complexity

Below is a wonderful guest post case study that discusses alcohol and warfarin use – Please feel free to donate your case to medication education by contacting me

Management of anticoagulation using warfarin is well established with the use of algorithms/protocols which result in the achievement and maintenance of therapeutic levels. However, with a narrow therapeutic index and a wide inter-individual variability in therapeutic response, warfarin does not come without its complexities.   There are a myriad of factors that contribute to these complexities. Due to complicated pharmacokinetic proprieties of warfarin, INR variability is expected within the first few days of initiation. The case below illustrates the complexity of warfarin dosing.

A 53-year-old white female newly diagnosed with bilateral deep-vein thrombosis was consulted to a pharmacist-managed anticoagulation program for an INR goal of 2-3. Her past medical history consisted of chronic back pain, hypertension, COPD, and obstructive sleep apnea. Her medications include carvedilol 25mg PO BID, cyclobenzaprine 10mg PO every 8 hours, amlodipine 10mg PO daily, folic acid 1mg PO daily, salmeterol/fluticasone 250-50mcg inhalation BID, and zolpidem 10mg PO at bedtime. After 5 days of warfarin therapy, with doses ranging from 5-10 mg/day, the patient remained subtherapeutic with PT-INR ranges from 1-1.2. I was hesitant to blindly increase doses further for a patient that had never taken warfarin before without a clear reason as to why the INR was not increasing.   I could not find any reason for this after evaluating the patient’s history and all potential factors such as changes in diet or medications, infections, vomiting, diarrhea, renal and liver status, obesity, etc. It was at this point the ideas of genetic polymorphisms and true warfarin resistance entered the thought process. However, true warfarin resistance is very rare, less than 1% of all warfarin-treated patients, and I started to believe that the patient was “cheeking” her medication.

In interviewing the patient, which included a discussion of non-warfarin-related topics, it was discovered that the patient had a history of chronic alcoholism, which had not been documented in her medical record. Acute alcohol consumption increases warfarin’s effects by decreasing warfarin metabolism. As a result, patients need more frequent PT-INR monitoring because of an increased risk of bleeding. In these patients, it is also wise to initiate a lower warfarin dose a slower titration. However, with chronic alcohol ingestion, there is an increase in warfarin’s metabolism resulting in decreased anticoagulation and possibly subtherapeutic INR’s, which happened in this case. In chronic alcoholism, a more aggressive initiation of warfarin is required. As a result, the patient needed to be maintained on 15-18 mg/day of warfarin to achieve therapeutic levels.

There are many resources available for not only pharmacists, but also other healthcare professionals to use for drug interactions such as It is an excellent tool to obtain more information regarding the monitoring and management of medications interacting with alcohol.  When conducting a medication reconciliation session with a patient, it is also helpful to ask about medical history because the pharmacist may be able to elicit information that the patient does not divulged to other health care members. Never assume anything about a patient without doing further investigations.

Submitted by:

Mike S. Jung, PharmD – PGY1 Pharmacy Practice Resident [email protected]

In collaboration with – Donna M. Lisi, PharmD, BCPS, BCPP; [email protected]

Please take advantage of this free resource – 30 Medication Mistakes seen in everyday practice.  It is a resource I created based upon my real world experiences, available free to subscribers.  Pharmacists, Nurses, students and Prescribers will benefit from this information!



  1. Sinxadi P and Blockman M. Warfarin resistance. Cardiovasc J Afr. 2008 Jul-Aug;19(4):215-7.
  2. Havrda DE, Mai T, Chonlahan J. Enhanced antithrombotic effect of warfarin associated with los-dose alcohol consumption. Pharmacotherapy. 2005;25:303-7.
  3. National Institute on Alcohol Abuse and Alcholism. Alcohol-medication interactions. Available from: Accessed 10/28/14@1:40PM.


  1. Cole Sloan

    Interesting case, would love to see references and MOA on the EtOH + Warfarin interaction discussed.

  2. BC

    Nice article Mike; good to know about warfarin and alcohol. So with Thanksgiving, Christmas, and New Year’s coming up, besides total abstinence if possible, what suggestions/points do you give patients as it relates to warfarin and acute alcohol consumption (e.g. if they want to have a beer when they watch Eagles beat the Cowboys (hopefully!), or if they want to enjoy that new bottle of wine they got from their adult son for Christmas, or if they want to ring in 2015 with a fine champagne)?

    By the way, way to represent NJ, and thanks for citing an article written by one of my professors during pharmacy school days! So my opinions of this article are *slightly* biased, but I seriously enjoyed the read.

  3. Mike Jung

    Thank you very much for your comment. It’s always nice to see one of our professors that we learned from being noted in literature.
    In terms of my advice on warfarin and acute alcohol consumption, it is okay to drink alcohol in moderation, meaning 1-2 servings of alcohol occasionally. Large variations in the amount of alcohol consumed on a day to day basis are definitely not advised. Binge drinking, defined by the National Institute on Alcohol Abuse and Alcoholism as a pattern of drinking that brings a person’s blood alcohol concentration (BAC) to 0.08 grams percent or above (men > 5 drinks, and women > drinks in about 2 hours) has a high probability of increasing bleeding risk. Generally, INR is unlikely to be affected with small or moderate amount of drinking. However, it would also be wise to monitor your INR throughout this time as individual’s response to alcohol varies and this could lead to different metabolic patterns of warfarin for each individual. It would be prudent to consult one’s doctor before any actions are taken.
    The references I used for this case report are listed above:
    1. Havrda DE, Mai T, Chonlahan J. Enhanced antithrombotic effect of warfarin associated with los-dose alcohol consumption. Pharmacotherapy. 2005;25:303-7.
    2. National Institute on Alcohol Abuse and Alcholism. Alcohol-medication interactions. Available from: Accessed 10/28/14@1:40PM.
    These two include information regarding chronic alcoholism and warfarin.
    The references as per my recommendations for acute alcohol drinking are as follows:
    1. Fiumara K and Goldhaber SZ. A patient’s guide to taking Coumadin/warfarin. Circulation. 2009;119:e220-222.
    2. Chock, AWY, Stading JA, and Sexson E. Food and lifestyle interactions with warfarin: a review. US Pharm. 2009;34(2):28-39.


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Written By Eric Christianson

November 5, 2014

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