Atazanavir and fosamprenavir levels are reduced by
H2-receptor antagonists such as ranitidine, probably by affecting gastric acidity. Amprenavir is predicted to be similarly affected. Not all
H2-receptor antagonists have been studied, but they would be expected to interact similarly. Saquinavir levels may be markedly increased by
cimetidine.
To avoid any interaction the manufacturers suggest that atazanavir/ritonavir should be given once daily with food, 2 hours before and at least 10 hours after the dose of the H2-receptor antagonist. The UK manufacturer suggests that no fosamprenavir dose adjustment is needed with ranitidine or other H2-receptor antagonists; however, the US manufacturer says the combination should be used with caution because fosamprenavir may be less effective. Increased monitoring should be considered to check for saquinavir adverse effects if
cimetidine is given.