2. The PENICILLINSSee Table 84-1, p. 1060 Lehne; Table 43-2, p. 790 Katzunga. Kinetics:Absorption: Absorption of the various penicillins after oral administration differs greatly depending on acid stability. Give penicillins po 1 h ac or 2 hr pc. Special dosage forms are available for IM injections to provide a slow absorption.Distribution: Penicillins are not lipid soluble and do not enter living cells well, however, penetration is increased by inflammation. Blood levels and half-life are increased by concomitant administration of probenecid, which interferes with renal elimination.Elimination: Most penicillins are as such (i.e., not metabolized) 10% by glomerular filtration & 90% by tubular secretion; some (e.g., nafcillin) are largely eliminated via the biliary tract.b. Specific penicillin groups(1). Penicillin G - the Benzylpenicillins(a). The benzylpenicillins are the drug of choice for treating pneumococcal, streptococcal & meningococcal infections and penicillin-sensitive staphylococcus as well as t.pallidus, actinomycosis, and clostridial infections (anaerobic).CDC updated their guidelines for preventing perinatal group B streptococcal disease (the leading cause of neonatal mortality), recommending penicillin G as the drug of choice with ampicillin as the alternative (Morantz CA. Am Fam Physician 2003;67:1121).(b). Narrow spectrum (primarily gram positive organisms and some gram negative cocci). Largely destroyed by gastric acid when given PO. Not metabolized but are rapidly excreted, largely by tubular secretion (inhibited by probenecid). These water soluble penicillins must cross the bacterial peptidoglycan cell wall to reach the PBP. Gram positive organisms have cell walls that are easily crossed by penicillins. Gramnegative organisms have an outer lipopolysaccharide membrane that presents a barrier to the water-soluble penicillins. (See LehneFigure 84-3, p. 1061)(c). »Penicillin GSod or Pot may be administered IM (painful), or IV (thrombophlebitis). It has a fast onset and short (3 hr) duration of action. Neonatal: Warning: use only aqueous crystalline penicillin G for IV administration. Sometimes known as benzylpenicillin, do not confuse this with benzathine penicillin which is given IM. For meningitis, Neofax suggests 75,000 to 100,000 units/kg/dose by IV infusion over 30 minutes or IM.