Four-drug regimens

In an attempt to improve the effectiveness of NRTI-only regimens, some researchers have explored combinations that include four rather than three drugs.

The randomised Trizivir Induction/Maintenance Study compared AZT/3TC/abacavir/tenofovir against AZT/3TC/efavirenz in more than 100 treatment-naive patients. After 48 weeks, similar proportions in both groups had a viral load below 50 copies/ml (68 vs 67%, respectively) and CD4 cell count gains were also comparable. Rates of discontinuation due to side-effects were similar, but people in the efavirenz group were more likely to have increased cholesterol levels.¹

After the triple-NRTI arm of ACTG 5095 was halted, the researchers tried an intensification strategy in which 170 patients who had achieved viral suppression on AZT/3TC/abacavir were randomly assigned to add either tenofovir or efavirenz. After 72 weeks, more than 75% in both arms had a viral load below 50 copies/ml.

Overall, slightly more people in the NRTI-only group experienced treatment failure (21 vs 15%); however, early treatment failure was more common in the efavirenz arm, while late treatment failure occurred more often with tenofovir. The researchers concluded that the safety, tolerability, and efficacy of the two regimens were not significantly different.²