since double ester prodrugs of penicillins , such as the pivaloyloxymethyl ester of ampicillin , are readily hydrolysed in plasma to yield the parent penicillin although at a rate lower than e.g . that of inactivation of a simple methyl ester , the plasma enzyme apparently attacking the beta-lactam bond of penicillin esters appears to have a high degree of specificity for the ester structure .
C0282215
beta-lactam
C0030842
penicillin