The approval of Isentress is based on data from two clinical trials involving 699 highly treatment experienced HIV-positive adults. Isentress, when combined with other approved ARVs, reduced viral loads to undetectable in up to 62 percent of the patients who received the drug, compared to 36 percent of those who received a placebo plus other HIV drugs.  

The side effects most commonly reported among study volunteers who received Isentress were diarrhea, nausea, and headache.  Blood tests showed abnormally elevated levels of a muscle enzyme—creatine kinase—in some patients receiving Isentress.  According to the FDA, Isentress should be used with caution by patients who are at increased risk for muscle problems like myopathy and rhabdomyolysis, which includes patients using other medications known to cause these conditions.

Isentress works by blocking HIV’s integrase enzyme. After HIV's genetic material is deposited inside a cell, its RNA must be converted (reverse transcribed) into DNA. The integrase enzyme helps to hide HIV's DNA inside the cell's DNA. Integrase inhibitors stop this process and prevent HIV DNA from meshing with healthy cell DNA.

While preliminary clinical trial results suggest that Isentress is comparable to Sustiva (efavirenz) among first-time treatment takers, it has not yet been approved for this HIV-positive population. The safety and efficacy of Isentress in HIV-positive children and pregnant women have also yet to be reviewed by the agency.