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[email protected]:40PM.

Written By Eric Christianson

November 5, 2014

Free PDF – Top 30 Medication Mistakes

Enjoy the blog?  Over 6,000 healthcare professionals follow the blog, why aren't you? Subscribe now and get a free gift as well!

Explore Categories