Coadministration has not been studied but based on metabolism and clearance a clinically significant interaction is unlikely. Roxatidine acetate is rapidly metabolised by esterases to its active metabolite roxatidine. Metabolism of roxatidine involves minimal contribution from CYP enzymes (CYP2A6 and CYP2D6). Raltegravir is mainly metabolized by UGT1A1. Raltegravir is unlikely to affect roxatidine metabolism. Roxatidine is unlikely to affect UGT1A1. Coadministration of famotidine and twice daily raltegravir (400 mg twice daily) increased raltegravir AUC, Cmax and C12h by 44%, 60% and 6%. Population PK analysis showed that the effect of gastric pH altering agents on the pharmacokinetics of once daily raltegravir was minimal (~9% decrease in relative bioavailability) and was not statistically or clinically significant. Concomitant use of raltegravir with proton pump inhibitors and H2 receptor antagonists did not result in a unique safety signal in Phase 3 studies. No dose adjustment is required with twice daily or once daily raltegravir.