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Ampicillin is a bactericidal antibiotic, it penetrates into the bacterial wall better than penicillin G and is active against gram-negative bacteria that are resistant to penicillin G. Ampicillin has a broad-spectrum antimicrobial activity and is the most widely used antibiotic for treating infections caused by Listeria, β-lactamase-negative Haemophilus, enterococci, Shigella, streptococci, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Neisseria gonorrhea, Neisseria meningitis and many coliform organisms. Ampicillin is excreted unchanged in the urine. In neonates with a gestational and postnatal ages of ≤ 34 weeks and ≤ 7 days, respectively, the half-life, the clearance and the distribution volume of ampicillin are 5.0 hours, 0.055 l/h/kg, and 0.40 l/kg, respectively. The ampicillin half-life decreases and the clearance of ampicillin increases with the neonatal maturation whereas the distribution volume is not affected by the neonatal maturation. Ampicillin may be administered orally. Ampicillin penetrates into the cerebrospinal fluid, especially when the meninges are inflamed. The recommended dose of ampicillin is 50 mg/kg every 12 hours in the first week of life, every 8 hours in neonates 1-3 weeks old, and every 6 hours in neonates 4 or more weeks old. Bacteremia, caused by group B Streptococcus, is treated with 150 to 200 mg/kg/day ampicillin and meningitis is treated with 300 to 400 mg/kg/day ampicillin in divided doses. Some organisms are resistant to ampicillin and a combination of gentamicin and a third-generation cephalosporin is recommended. The aim of this study is to review the effects and pharmacokinetics of ampicillin in neonates and infants.