Ampicillin

Lore & Background

Ampicillin was the first broad-spectrum penicillin, active against both gram-positive and some gram-negative bacteria. It works by inhibiting transpeptidase, an enzyme needed for bacterial cell wall synthesis, leading to cell lysis. Its spectrum includes Streptococcus pneumoniae, some Staphylococcus aureus, Enterococcus, Neisseria meningitidis, and some Haemophilus influenzae, though many Enterobacteriaceae and Pseudomonas are resistant. Co-administration with sulbactam enhances its activity by inhibiting beta-lactamase.

Reader's Guide

Ampicillin remains a cornerstone antibiotic, particularly for respiratory and urinary tract infections, meningitis, and endocarditis. It is also used prophylactically in pregnant women carrying group B streptococci and in those with rheumatic heart disease. Its safety in pregnancy and breastfeeding is well established, though dose adjustments may be needed in kidney impairment. The emergence of resistant strains, especially in gonorrhea, has limited some historical uses. Despite this, its inclusion on the WHO Essential Medicines list underscores its ongoing importance, especially in combination therapies for multidrug-resistant Enterococcus. Common side effects include diarrhea and rash; serious risks include anaphylaxis and C. difficile colitis.

Did You Know?

• Ampicillin was the first broad-spectrum penicillin, active against both gram-positive and some gram-negative bacteria.
• It is one of the few antibiotics effective against multidrug-resistant Enterococcus faecalis and E. faecium.
• Over 40% of patients with mononucleosis develop a skin rash when taking ampicillin.