Warning: do not combine Reyataz and Prilosec.

A new study has found that if Reyataz (atazanavir), whether taken with or without ritonavir, is used with Prilosec (omeprazole, a proton-pump inhibitor used to reduce stomach acidity, for treating acid-reflux disease or other conditions), the blood level of atazanavir is reduced by three quarters or more, probably making it ineffective and leading to viral resistance. A December 2004 warning from Bristol-Meyers Squibb and the FDA said that doctors should not coadminister atazanavir (with or without ritonavir) with omeprazole. (This was already the recommendation before the new warning, but now the seriousness of the problem is more clear.)

Another kind of medicine to reduce stomach acidity, H2-receptor antagonists (such as Zantac, Tagamet, etc.) might also lower atazanavir levels; a study to find out is now ongoing. Until its results are available the following warning is included in the Reyataz label (full prescribing information for physicians), as of December 2004:

"Reduced plasma concentrations of atazanavir are expected if H2-receptor antagonists are administered with REYATAZ (atazanavir sulfate). This may result in loss of therapeutic effect and development of resistance. To lessen the effect of H2-receptor antagonists on atazanavir exposure, it is recommended that an H2-receptor antagonist and REYATAZ be administered as far apart as possible, preferably 12 hours apart."

For more information check the current label, available at http://www.reyataz.com. See the "patient information" or "full prescribing information" links (in early January 2004 these worked with some but not all Web browsers).