ampicillin
Brand: Principen
Prototype: penicillin-g
Drug Class: antibiotic (penicillin)
Drug Family: antibiotic
Subclass: aminopenicillin
Organ Systems: infectious-disease
Mechanism of Action
Inhibits PBPs and bacterial cell wall synthesis like all penicillins, but the aminophenyl side chain extends coverage to include gram-negative organisms (E. coli, H. influenzae, Proteus). However, ampicillin-resistant strains producing beta-lactamase are prevalent; combination with sulbactam (Unasyn) restores activity.
penicillin-binding proteins (PBPs)transpeptidase
Indications
- bacterial meningitis (Listeria, Group B Streptococcus)
- enterococcal infections (often combined with gentamicin)
- urinary tract infections (ampicillin-sensitive organisms)
- intrapartum GBS prophylaxis
Contraindications
- penicillin allergy (anaphylaxis)
- infectious mononucleosis (causes ampicillin rash)
Adverse Effects
Common
- diarrhea
- nausea
- rash (especially in EBV mononucleosis)
- injection site reactions
Serious
- anaphylaxis
- C. difficile colitis
- seizures at high doses (especially with renal impairment)
Pharmacokinetics (ADME)
| Absorption | oral bioavailability ~40%; IV provides full bioavailability |
| Distribution | protein binding ~15-25%; penetrates CSF in meningitis (inflamed meninges) |
| Metabolism | minimal hepatic |
| Excretion | primarily renal (60-90% unchanged); dose adjustment in renal impairment |
| Half-life | 1-1.9 hours |
| Onset | rapid IV |
| Peak | 1 hour IM; end of infusion IV |
| Duration | 6 hours |
| Protein Binding | 15-25% |
| Vd | 0.28 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| allopurinol | increases ampicillin rash incidence 3-10 fold | moderate |
| aminoglycosides | synergistic for enterococcal infections; incompatible in same IV line (physically incompatible) | moderate |
Nursing Considerations
- Intrapartum GBS prophylaxis: 2 g IV loading dose then 1 g IV every 4 hours until delivery in penicillin-non-anaphylactic-allergic patients.
- Ampicillin and aminoglycosides (gentamicin) are physically incompatible; must be administered through separate IV lines or at different times.
- Maculopapular rash in patients with EBV mononucleosis or CLL is not a true IgE-mediated allergy but indicates ampicillin should not be used for concurrent infection.
- Ampicillin is preferred over penicillin G for Listeria meningitis because of better oral penetration and activity profile.
Clinical Pearls
- Ampicillin is one of the few antibiotics with activity against Listeria monocytogenes, the cause of meningitis in immunocompromised patients, elderly, and neonates; empiric meningitis regimens must include ampicillin in these populations.
- For enterococcal endocarditis, ampicillin plus gentamicin provides synergistic bactericidal activity; ampicillin alone is bacteriostatic against enterococci, which is insufficient for endocarditis treatment.
Safety Profile
Pregnancy safe
Lactation use-with-caution
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.