Which of the following penicillins is resistant to penicillinase?

Cloxacillin is the penicillin that is specifically designed to be resistant to penicillinase, which is an enzyme produced by certain bacteria that can inactivate many penicillins. This property allows cloxacillin to effectively treat infections caused by penicillinase-producing staphylococci and other resistant bacteria.

In contrast, Penicillin G, Penicillin VK, and Bicillin LA are more susceptible to inactivation by penicillinase. They cannot withstand the enzymatic breakdown, making them less effective against bacteria that produce this enzyme. Cloxacillin's unique structure, which includes a bulky side chain, helps it avoid being targeted by the penicillinase enzyme, thereby maintaining its antibacterial efficacy against resistant strains.