Smoking and Warfarin

Q: Smoking tends to  ______________  the dose requirement of warfarin? (select one)

A) Increase
B) Decrease


Answer: A

Smoking tends to increase the dose requirement of warfarin by about 10-12 percent. The increase clearance of warfarin in smokers is probably due to induction of hepatic cytochrome P-450 activity (eg, CYP1A1, CYP1A2, CYP2E1) by polycyclic aromatic hydrocarbons, and not by nicotine in the cigarette smoke. Similar effects can happen in marijuana smoking.

#pharmacology


References: 

1. Nathisuwan S, Dilokthornsakul P, Chaiyakunapruk N, et al. Assessing evidence of interaction between smoking and warfarin: a systematic review and meta-analysis. Chest 2011; 139:1130. 

2. Yamreudeewong W, Wong HK, Brausch LM, Pulley KR. Probable interaction between warfarin and marijuana smoking. Ann Pharmacother 2009; 43:1347.