Interaction of staphylococcal penicillinase and 6-[D(-)-alphaguanidino-phenylacetamido]-penicillanic acid

6[d(-)-alpha-Guanidinophenylacetamido]-penicillanic acid was shown to be significantly hydrolyzed by only one of six preparations of staphylococcal penicillinase. This penicillin analogue is a stronger penicillinase inactivator than are nafcillin and methicillin, which were not significantly hydrolyzed by the enzyme.