As outlined in Chapter 5, drug interactions in human immunodeficiency virus (HIV) are encountered frequently, particularly with protease inhibitors and nonnucleoside reverse transcriptase inhibitors (NNRTIs). In a retrospective chart review of 165 HIV patients newly prescribed a protease inhibitor, at least one potential drug interaction was identified in 82 (49.7%) of the patients (1). In total, 111 interactions were identified, but only 22 (19.8%) were recognized at the time of protease inhibitor therapy initiation. An additional 12 drug interactions were later identified at follow-up, but 77 (69.3%) were never recognized. At the time this study was conducted, only three protease inhibitors (saquinavir, ritonavir, and indinavir) were available. More recently, in a chart review of 189 ambulatory HIV patients, 466 interactions were identified in 153 subjects for an average of 2.46 interactions per patient (2).