Penicillins

The penicillins interfere with cell wall synthesis and are bactericidal. They are excreted in the urine in therapeutic concentrations - indeed the first person to be given penicillin had the excreted drug extracted from his urine and re-administered since only small amounts of the drug could be produced at that time.

Probenecid blocks the renal tubular excretion of the penicillins and produces higher and more prolonged plasma concentrations.

Other improvements since the original development include:-

• acid stability to allow oral administration
• improved spectrum, for example with ampicillin, which has gram negative activity but at the expense of gram positive activity
• insoluble preparations to prolong serum levels, for example in procaine penicillin