Bioavailability and metabolism of talampicillin

Talampicillin is an ester of ampicillin which is readily hydrolysed on absorption to release ampicillin. It is well absorbed from the gastro-intestinal tract resulting in a greater bioavailiability of ampicillin than can be achieved with equivalent doses of ampicillin itself. Dose response studies have confirmed a direct relationship between the dose of talampicillin administered and peak serum ampicillin concentration and urinary excretion of ampicillin. Dosing of ampicillin after food has been shown to adversely affect the total bioavailability of ampicillin. This is not so after dosing with talampicillin. The bioavailability of ampicillin from a 250-mg Talpen tablet dosed after a large meal was significantly greater than that from 250 mg ampicillin dosed in the fasting state. Studies in volunteer subjects at multiples of the proposed therapeutic dose for periods of up to 28 days have indicated its acceptability, bioavailability and lack of side effects on repeated dosing. The fate of the phthalidyl moiety of talampicillin has been investigated in repeated dose studies and in a single dose studies and in a single dose study in which radiolabelled talampicillin was administered. The principal metabolite of the phthalidyl moiety in man has been shown to be 2-hydroxymethylbenzoic acid, which is identical to that in experimental animals used for toxicological investigations.