Ampicillin (Omnipen, Principen)

Prophylaxis timing - Give within 60 minutes before incision for surgical prophylaxis; redose intraoperatively every 2 hours or after high blood loss.

Cross-reactivity - Shares a beta-lactam ring with cephalosporins; true cross-reactivity is low (~1-2%) but ask about the nature of any penicillin allergy before giving.

Anaphylaxis readiness - Have epinephrine and airway support available; beta-lactams are a leading cause of perioperative anaphylaxis.

Drug Interactions - Probenecid raises and prolongs levels; may reduce efficacy of oral contraceptives; allopurinol increases rash incidence.

Pediatric Implications - Weight-based dosing (50 mg/kg), widely used for neonatal/pediatric prophylaxis and group B strep coverage; well tolerated.

Obstetric Implications - Category B, crosses the placenta; a mainstay for intrapartum GBS prophylaxis. Compatible with breastfeeding.

Relative:

Infectious mononucleosis (high rash risk)

Significant renal impairment (dose-adjust)

Caution:

History of any beta-lactam reaction

Surgical prophylaxis: 2 g IV within 60 min of incision (adult); 50 mg/kg (pediatric).

Redose every 2 hours intraoperatively.

Binds penicillin-binding proteins, inhibiting bacterial cell-wall peptidoglycan cross-linking, producing cell lysis.

Minimal hepatic

Renal

Give slow IV push over 3-5 min or short infusion; reconstitute and use promptly. Refrigerate reconstituted solution and discard per label.