Penicillin compositions

A method for the treatment of bacterial infections in humans comprising orally administering to a human in need thereof a composition of a pharmaceutically acceptable carrier together with an antibacterially effective amount of a methicillin ester of formula (III):

• ##STR14## or a pharmaceutically acceptable acid addition salt thereof, wherein A is C.sub.1-6 alkylene unsubstituted or substituted by methyl or ethyl, and R.sup.2 and R.sup.3 are the same or different and each is C.sub.1 -C.sub.6 alkyl, the composition being in oral dosage form.