Vatacil Mechanism of Action

Pharmacology: Pharmacokinetics: Absorption and Fate: Ampicillin is given by injection as the sodium salt and following the intramuscular administration of 500mg peak plasma concentrations occur within about 1 hour and are reported to range from 7-14 uq per mL. Ampicillin is widely distributed and therapeutic concentrations can be achieved in ascitic pleural and joint fluids. It crosses the placenta into the fetal circulation and small amounts are excreted in breast milk. There is little diffusion into the cerebrospinal fluid except when the meninges are inflamed. About 20% is bound to plasma proteins and the plasma half-life about 1-1.5 hours, but this may be increased in neonates and the elderly; in renal failure half-lives of 7-20 hours have been reported.
Ampicillin is metabolized to some extent to penicilloic acid, which is excreted in the urine. Renal clearance of ampicillin occurs partly by glomerular filtration and partly by tubular secretion; it is retarded by the concomitant administration of probenecid. Ampicillin is the least serum-bound of all penicillins, averaging about 20% compared to approximately 60-90% for other penicillins. Following parenteral administration about 60 to 80% is excreted in the urine within 6 hours. High concentrations are reached in bile; it undergoes enterohepatic recycling and some is excreted in the feces.
Microbiology: Ampicillin is a beta-lactam antibiotic. It is bactericidal and has a similar mode of action to that of benzylpenicillin but as an amino-penicillin with an amino group side chain attached to the basic penicillin structure, ampicillin is better able to penetrate to outer membrane of some Gram negative bacteria and has broader spectrum of activity. It resembles benzylpenicillin in the action against Gram-positive organisms including Streptococcus pneumoniae and other streptococci but, apart perhaps from Enterococcus faecalis, it is slightly less potent than benzylpenicillin. Listeria monocytogenes is highly sensitive. The Gram negative cocci Moraxella (Bramhamella) catarrhalis; Neisseria gonorrhea and N. meningitidis are sensitive. Ampicillin is more active than benzylpenicillin against some Gram negative bacilli including Haemophilus influenza and Enterobacteriacea such as Escherichia coli, Proteus mirabilis, Salmonella and Shigella spp. It is inactive against Pseudomonas aeruginosa. Ampicillin also has activity similar to benzylpenicillin against other organisms including many anaerobes and Actinomyces spp.