Drugmaker Bristol-Myers Squibb this week sent a letter to physicians warning them that blood-based concentrations of its protease inhibitor Reyataz are significantly lowered when acid-control agents, particularly Prilosec, also are taken. New data from an open-label, multiple-dose interaction study showed a 78% reduction in trough concentrations of Reyataz when taken with a small booster dose of Norvir and 40 milligrams of Prilosec. Based on the study, BMS urges doctors not to administer Reyataz with or without a booster dose of Norvir in combination with Prilosec. BMS officials aren't sure whether over-the-counter 20-milligram doses of Prilosec have the same effect on blood-based levels of Reyataz, and therefore do not recommend combining the treatments. Investigations of the interaction between Reyataz and H2-receptor antagonists--another class of gastric medications--are still ongoing. Until data from the studies are available, BMS is warning physicians that lower blood-based levels of Reyataz could occur when the drugs are combined.