IMPORTANCE OF THE FIELD: Antiretroviral therapy exhibits significant potential 
to alter the metabolism of other medications. Warfarin is widely used for the 
management of clotting disorders and is prone to drug-drug interactions that can 
result in subtherapeutic anticoagulation or over-anticoagulation.
AREAS COVERED IN THIS REVIEW: The mechanism and clinical significance of 
drug-drug interactions between warfarin and individual antiretrovirals are 
discussed. Literature searches were conducted in August of 2009 using multiple 
databases including Medline (1950 - 2009), EMBASE (1980 - 2009), International 
Pharmaceutical Abstracts (1970 - 2009) and the Cochrane Database of Systematic 
Reviews. The following search terms were utilized: warfarin, HIV, 
antiretroviral, drug interaction, protease inhibitor (PI), non-nucleoside 
reverse-transcriptase inhibitor (NNRTI), cytochrome P450 (CYP450), CYP2C9 and 
individual antiretrovirals by name. The manufacturers of PIs and NNRTIs were 
also contacted regarding unpublished data.
WHAT THE READER WILL GAIN: Clinicians will gain an understanding of the 
antiretrovirals that are prone to alter warfarin metabolism and the implications 
for warfarin dose modification.
TAKE HOME MESSAGE: Metabolic interaction between warfarin and antiretrovirals is 
likely, particularly if NNRTIs or PIs are included in the antiretroviral 
regimen. Titration of warfarin dose should be conducted on the basis of close 
monitoring of the international normalized ratio. Empiric warfarin dose 
modifications should be considered for individual antiretrovirals.