Why should acid suppressants such as cimetidine, ranitidine, and omeprazole be dosed 2 hours apart from Risperdal?

• A. They are inhibitors and decrease Risperdal absorption
• B. They increase Risperdal absorption
• C. They cause QT prolongation
• D. They increase hepatic metabolism of Risperdal

Answer: (A)

The key idea is that gastric pH–altering drugs can change how well certain medications are absorbed. Risperidone is a weak base, and its solubility decreases when stomach pH is raised. Acid suppressants like cimetidine, ranitidine, and omeprazole raise gastric pH, which can reduce risperidone dissolution and absorption, leading to lower blood levels. By dosing acid suppressants a couple of hours apart from risperdal, you minimize the overlap of their effects, allowing risperidone to be absorbed more reliably before the stomach environment becomes less acidic. While some acid suppressants can modestly affect metabolism via CYP enzymes, the clinically relevant interaction here is decreased absorption, not increased metabolism or other effects.