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Original Research: ANTITHROMBOTIC THERAPY |

Assessing Evidence of Interaction Between Smoking and Warfarin: A Systematic Review and Meta-analysis

Surakit Nathisuwan, PharmD, BCPS; Piyameth Dilokthornsakul, PharmD; Nathorn Chaiyakunapruk, PharmD, PhD; Tatiya Morarai, PharmD; Thararat Yodting, PharmD; Nichakorn Piriyachananusorn, PharmD
Author and Funding Information

From the Clinical Pharmacy Division, Department of Pharmacy, Faculty of Pharmacy (Dr Nathisuwan), Mahidol University, Bangkok, Thailand; Center of Pharmaceutical Outcomes Research (Drs Dilokthornsakul and Chaiyakunapruk) and Department of Pharmacy Practice (Drs Dilokthornsakul, Chaiyakunapruk, Morarai, Yodting, and Piriyachananusorn), Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok, Thailand; School of Population Health (Dr Chaiyakunapruk), University of Queensland, Brisbane, QLD, Australia; and School of Pharmacy (Dr Chaiyakunapruk), University of Wisconsin, Madison, WI.

Correspondence to: Nathorn Chaiyakunapruk, PharmD, PhD, Center of Pharmaceutical Outcomes Research, Department of Pharmacy Practice, Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok, Thailand 65000; e-mail: chaiyakunapr@wisc.edu


Funding/Support: This work was supported by Thai Pharmacy Network for Tobacco Control under the Thai Health Promotion Foundation.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2011 American College of Chest Physicians


Chest. 2011;139(5):1130-1139. doi:10.1378/chest.10-0777
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Background:  Chronic smoking, theoretically, can interfere with warfarin metabolism through enzyme-inducing effects of polycyclic aromatic hydrocarbons. However, clinical evidence of interactions between warfarin and smoking are inconclusive. This study aimed to systematically review all relevant clinical evidence of this interaction.

Methods:  We performed a systematic search using computerized databases, including PubMed, Embase, Cochrane Central Register of Controlled Trials, CINAHL, Allied and Complementary Medicine, PsycINFO, International Pharmaceutical Abstracts, and ClinicalTrials.gov from 1966 to December 2008. Keywords included “warfarin” with “smoking,” “tobacco,” “cigarette,” and “polycyclic aromatic hydrocarbons.” Original articles reporting interaction between warfarin and smoking were included. All articles were reviewed independently by two investigators for study design, population, outcomes, and quality of evidence.

Results:  Of the 1,240 studies retrieved, one experimental pharmacokinetic study and 12 cross-sectional studies were included. The pooled analyses of multivariate studies suggested that smoking was associated with a 12.13% (95% CI, 6.999-17.265; P < .001) increase in warfarin dosage requirement and an additional 2.26 mg (95% CI, 2.529-7.042; P = .355) per week compared with nonsmoking. Additional sensitivity analysis of four multivariate studies with adjustment for pharmacogenomic factors suggested that smoking was associated with a 13.21% (95% CI, 8.59%-17.83%; P < .001) increase in warfarin dosage requirement compared with nonsmokers. Results of an experimental pharmacokinetic study lend theoretical support to the findings.

Conclusions:  Evidence suggests that smoking may potentially cause significant interaction with warfarin by increasing warfarin clearance, which leads to reduced warfarin effects. Close monitoring of warfarin therapy should be instituted when there is a change in smoking status of patients requiring warfarin therapy.

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