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Pharmacology: Pharmacokinetics: Ampicillin is relatively resistant to inactivation by gastric acid and is moderately well absorbed from the gastrointestinal tract after oral doses. Food can interfere with the absorption of Ampicillin so doses should preferably be taken at least 30 minutes before meals. Peak concentrations in plasma are attained in about 1 to 2 hours and after a 500 mg oral dose be reported to range from 3 to 6 micrograms/mL. Peak plasma concentrations of Ampicillin after a 500 mg intramuscular dose given as the sodium salt occur within 1 hour and are reported to range from 7 to 14 micrograms/mL.
Ampicillin is widely distributed and therapeutic concentrations can be achieved in ascitic, pleural, and joint fluids. It crosses the placenta and small amounts are distributed into breastmilk. There is little diffusion into the CSF except when the meninges are inflamed. About 20% is bound to plasma proteins and the plasma half-life is about 1 to 1.5 hours, but this may be increased in neonates, the elderly, and patients with renal impairment; in severe renal impairment half-lives of 7 to 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 reduced by probenecid. About 20 to 40% of an oral dose may be excreted unchanged in the urine in 6 hours; urinary concentrations have ranged from 0.25 to 1 mg/mL following dose of 500 mg. After parenteral use about 60 to 80% is excreted in the urine within 6 hours. Ampicillin is removed by hemodialysis. High concentrations are reached in bile; it undergoes enterohepatic recycling and some is excreted in the faeces, Ampicillin with Sulbactam. The pharmacokinetics of Ampicillin and Sulbactam are broadly similar and neither appears to affect the other or to any great extent.
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