Switching from protease inhibitors to efavirenz: differences in efficacy and tolerance among risk groups: a case-control study from the Swiss HIV Cohort.

OBJECTIVES Many patients have simplified their therapy by replacing protease inhibitors (PI) with efavirenz. In a large cohort study representative of clinical practice, we compared outcomes in patients who replaced PI with efavirenz (switchers), with patients who continued on PI (non-switchers). We investigated the likelihood of virological failure in switchers and non-switchers, and the tolerance of efavirenz-containing regimens in different transmission risk groups. DESIGN, SETTING, AND METHODS Using the database of the Swiss HIV Cohort Study, we identified patients who switched from PI-containing to efavirenz-containing highly active antiretroviral therapy for reasons of tolerance, toxicity, or convenience. Switchers were matched to non-switchers on the basis of calendar time, CD4 cell count, and viral load. RESULTS The probability of virological failure was less in patients who switched to efavirenz values after one year: 9.4% [95% confidence interval (CI) 5.5-15.9] versus 27.2% (95% CI 21.5-34.1), odds ratio (OR) for failure 0.34. The effect was more pronounced when injection drug users (IDU) were omitted from the analysis (OR 0.19, 95% CI 0.09-0.43); it was absent in IDU (OR 0.95, 95% CI 0.44-2.04). IDU stopped efavirenz more frequently during the first 2 months of treatment than non-IDU [22.6% (95% CI 11.5-41.6) versus 6.6% (95% CI 3.6-11.8) at 2 months]. No difference between IDU and non-IDU was evident when the frequency of stopping indinavir or nelfinavir was measured. CONCLUSION Switchers had less virological failure and less chance of further treatment changes than non-switchers. However, efavirenz was less successful in IDU than in other transmission categories.