<prompt> All of the following drugs undergo hepatic metabolism before excretion, EXCEPT:PhenytoinDiazepamPenicillin GCimetidine  <response>: The pharmacokinetics of Penicillin G is dominated by very rapid renal excretion. About 10 of the drug is eliminated by glomerular filtration and rest by tubular secretion. The plasma t12 of penicillin G in healthy adults is 30 minutes. Ref: Essentials of Medical Pharmacology By K D Tripathi, 5th Edition, Pages 364, 372, 589, 655 