: Penicillins are generally excreted unchanged, (usually <20% metabolized). Penicilloic acid derivatives that are formed tend to be allergenic.

Excretion: Most (60-90%) of a parenterally administered penicillin is eliminated in the urine within a short time (eg, up to 90% of penicillin G within 6 hr), which results in high concentrations in urine.