10-20% by glomerular filtration and 80-90% by active tubular secretion --> Active secretion'is inhibited by probenacid which increases blood concentration of penicillin. o Penicillin acts by inhibiting cell wall synthesis. Also know o Penicillin G (benzyl penicillin) has a sho VA. So, it has to be given 6-12 hourly. o Procaine penicillin and benzathine penicillin (longest acting) are long acting due to slow release. o Extended (broad) spectrum penicillins (Aminopenicillins, Carboxypenicillins and ureidopenicillins) are active against gram negative organisms as well (in addition to gram positive oraganisms, though their activity against gram positive organisms is less than penicillin G). o Activity of penicillins against gram positive organisms --> Penicillin G (max) > Extendend spectrum penicilins > b- lactamase resistant penicillins (methicillin & others).">