Minor
Suspected
Description
Ranitidine may slightly increase phenytoin bioavailability through modest inhibition of CYP2C9, though the interaction is less significant than with cimetidine.
Mécanisme
Ranitidine inhibits CYP2C9 weakly, reducing phenytoin hydroxylation; additionally, raised gastric pH from H2 blockade may alter phenytoin absorption kinetics.
Signification clinique
Case reports describe phenytoin toxicity (nystagmus, ataxia) with ranitidine; the effect is variable and generally smaller than cimetidine's.
Prise en charge
Monitor phenytoin levels and watch for signs of toxicity when starting ranitidine; consider switching to a less interacting agent if needed.