GS 9350, an experimental pharmacokinetic (PK) booster from Gilead Sciences, is able to boost Reyataz (atazanavir) blood levels as successfully as Norvir (ritonavir) does. These data were reported at the 49th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in San Francisco and reported by aidsmap.

Low-dose Norvir currently has to be prescribed along with all of the existing protease inhibitors (PIs) in order to ensure that blood levels of the PIs remains stable. Unfortunately, Norvir comes with side effects such as stomach upset, diarrhea and elevations in triglycerides and cholesterol.

In answer to these problematic side effects, Gilead has developed a new PK booster that it hopes will boost other HIV drugs as well as Norvir does, without the problems associated with it. The authors of the study presented at ICAAC enrolled 42 HIV-negative volunteers to take Reyataz with either 100 mg or 150 mg of GS 9350 or 100 mg of Norvir for 10 days.

Reyataz levels in those taking Norvir were similar to those taking 150 mg of GS 9350 throughout the dosing period. Nine people stopped taking the drugs early. Most for mild side effects. Three people taking GS 9350 stopped taking the drug early due to a skin rash that resolved after people stopped the drug.

The authors conclude that GS 9350 appears to be well tolerated so far and might be a reasonable alternative to Norvir in people taking Reyataz.