Human pharmacokinetics and disposition of sarmoxicillin, a lipophilic amoxicillin prodrug

Sarmoxicillin, an amoxicillin prodrug, is the methoxymethyl ester of hetamoxicillin. Esterification converted amoxicillin from an amphoteric to a cationic compound and resulted in a 30- to 600-fold increase in lipid partitioning. Oral absorption studies in normal subjects demonstrated that sarmoxicillin was only partially hydrolyzed by nonenzymatic and gut or hepatic first-pass metabolism and that significant quantities of intact ester appeared in the systemic circulation. Sarmoxicillin was converted to amoxicillin in plasma by hydrolysis of the acetone penicinate and the methoxymethyl ester bonds. Significant amoxicillin levels were demonstrated in saliva after administration of sarmoxicillin, but not amoxicillin, over a 250- to 1,000-mg dose range. Differences in the absorption, distribution, or metabolism of amoxicillin were also evident in the lower plasma amoxicillin maximum concentration and area under the curve and longer half-life after sarmoxicillin administration. Differences in the distribution of this lipophilic ester could result in a significant increase in tissue penetration and subsequent therapeutic efficacy of amoxicillin when administered as sarmoxicillin.