Merck's HIV Drug Isentress Fails Once-a-Day Study

Taking the HIV drug Isentress once a day is not as effective as the standard twice-daily regimen, reported drug manufacturer Merck & Co. Based on these initial results, Merck is suspending the Phase III trial of once-daily dosing.

Isentress is the only HIV drug that works by blocking integrase, an enzyme that allows HIV to insert its genetic material into human DNA. Taken twice a day, Isentress is used among both previously treated and treatment-naive HIV patients.

The trial enrolled 775 patients who were taking other HIV medications in addition to Isentress. One subset received 800 milligrams of Isentress once-daily, another group received the standard 400-milligram dose twice per day.

After 48 weeks, HIV was lowered to undetectable levels in 83.2 percent of patients on the once-daily regimen and 88.9 percent of patients on the twice-daily schedule.

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