Ampicillin Classification
Ampicillin is a β-lactam antibiotic, specifically classified as an aminopenicillin, characterized by the presence of a β-lactam ring that inhibits bacterial cell wall synthesis. 1
Drug Class and Mechanism
Ampicillin belongs to the β-lactam class of antimicrobials, which exert their antibacterial effect by inhibiting cell-wall synthesis and producing autolysis through binding to penicillin-binding proteins (PBPs) in the bacterial cell wall 1
More specifically, ampicillin is an aminopenicillin, a subclass developed to provide gram-negative antimicrobial activity beyond the original penicillins 2
Ampicillin is described as "a less potent but better-absorbed derivative of ampicillin" in the context of comparing it to other penicillins, though this appears to be referring to amoxicillin as the derivative 1
Antimicrobial Spectrum
Ampicillin is bactericidal at low concentrations and clinically effective against gram-positive organisms usually susceptible to penicillin G, as well as a variety of gram-negative organisms 3
The drug's spectrum includes alpha- and beta-hemolytic streptococci, Streptococcus pneumoniae, non-penicillinase-producing staphylococci, Hemophilus influenzae, Neisseria gonorrhoeae, Proteus mirabilis, Salmonella, Shigella, and Escherichia coli 3, 2
Ampicillin is inactivated by penicillinase and therefore ineffective against penicillinase-producing organisms including certain staphylococci, Pseudomonas aeruginosa, and some strains of E. coli 3
Pharmacological Properties
Ampicillin is stable in the presence of gastric acid and well absorbed from the gastrointestinal tract, diffusing readily into most body tissues and fluids 3
In blood serum, ampicillin is the least protein-bound of all penicillins, with an average of only 20% bound to plasma proteins compared to 60-90% for other penicillins 3
The drug is excreted largely unchanged in the urine, and its excretion can be delayed by concurrent probenecid administration 3
Combination Formulations
Ampicillin is frequently combined with β-lactamase inhibitors (sulbactam or clavulanate) to extend its antibacterial spectrum and overcome resistance from β-lactamase-producing organisms 1, 4
When combined with sulbactam, the formulation (ampicillin-sulbactam) has broad spectrum activity against Gram-positive, Gram-negative, and anaerobic bacteria, with particular effectiveness against Acinetobacter baumannii due to sulbactam's intrinsic activity 4, 5