An 18-year-old man who is known to have non-penicillinase producing gonococcal urethritis is given an injection of penicillin and probenecid. What is the mechanism used by probenecid that makes penicillin more efficacious

PENICILLIN-G (BENZYL PENICILLIN) Pharmacokinetics :- Penicillin G is acid labile, therefore destroyed by gastric acid. As such, less than 1/3rd of an oral dose is absorbed in the active form. Absorption of sod. PnG from i.m. site is rapid and complete; peak plasma level is attained in 30 min. It is distributed mainly extracellularly; reaches most body fluids, but penetration in serous cavities and CSF is poor. However, in the presence of inflammation (sinovitis, meningitis, etc.) adequate amounts may reach these sites. About 60% is plasma protein bound. It is little metabolized because of rapid excretion. The pharmacokinetics of PnG is dominated by very rapid renal excretion; about 10% by glomerular filtration and the rest by tubular secretion. The plasma t 1/2 of PnG in healthy adult is 30 min. Neonates have slower tubular secretion-- t 1/2 of PnG is longer; but approaches adult value at 3 months and then is even shoer during childhood. Aged and those with renal failure excrete penicillin slowly. Tubular secretion of PnG can be blocked by probenecid--higher and longer lasting plasma concentrations are achieved. Probenecid also decreases the volume of distribution of penicillins. Ref:- kd tripathi; pg num:-718