Pharmacokinetics of roxatidine in healthy volunteers

This paper reviews those studies which investigated the absorption, distribution, metabolism and elimination of roxatidine acetate (formerly HOE 760) following its single and multiple oral administration to healthy male and female volunteers. Roxatidine acetate is almost completely (greater than 95%) absorbed after oral administration and is rapidly converted to roxatidine, its major active plasma and urinary metabolite. In common with many other prodrugs, the parent substance is not detectable in either plasma or urine and therefore all pharmacokinetic studies have been evaluated using measurements of roxatidine. A powder capsule formulation of the drug showed rapid absorption (tmax = 1 hour) and linear pharmacokinetics across the dose range 25 to 100mg, but produced some gastrointestinal intolerance. However, a granulated capsule formulation showed a much slower release (tmax = 3 hours) and was well tolerated. There was no evidence of any food interaction or interaction with other drugs such as antipyrine and propranolol. The plasma terminal half-life of the granulated capsule averaged 6 hours and between 55 and 60% of the dose was recovered in the urine as roxatidine. Following repeated daily administration of the prodrug, steady state plasma levels of roxatidine were reached on average by the fourth dose.