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Aminopenicillin Antibiotic Pregnancy: Animal studies show no teratogenic effects; extensive documented human use — may be considered appropriate when antibiotic therapy is required in pregnancy. Trace quantities of penicillins detected in breast milk during lactation.

Ampicillin

Brand names: Penbritin

Ampicillin is a broad-spectrum aminopenicillin antibiotic used for susceptible infections including certain respiratory, urinary, gastrointestinal and listerial infections.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 500 mg four to six times a day (septicaemia, endocarditis, osteomyelitis, peritonitis, intra-abdominal sepsis)
Route: IM or IV
Frequency: Four to six times a day, for one to six weeks
Doses per UK SPC (parenteral 500 mg product), guide only — may be increased in severe infections. Septicaemia, endocarditis, osteomyelitis, peritonitis, intra-abdominal sepsis: 500 mg four to six times a day IM or IV for one to six weeks. Meningitis: 2 g six-hourly IV (adult). Other routes may be used in conjunction with systemic therapy — intraperitoneal 500 mg daily; intrapleural 500 mg daily; intraarticular 500 mg daily; local use in abdominal surgery 1 g sterile powder into the wound. IV administration: dissolve 500 mg in 10 ml water for injections, give by slow injection over 3-4 minutes, or add to infusion fluids.

Paediatric dose

Dose: 150 mg/kg
Route: IV
Frequency: Daily in divided doses
UK SPC: for meningitis, children's dosage is 150 mg/kg daily IV in divided doses. General paediatric guidance: half adult routine dosage for children under 10 years. All dosages are a guide only and may be increased in severe infections. (Note: US FDA fallback label is for ampicillin/sulbactam combination — 300 mg/kg/day of the combination in children ≥1 year — not directly comparable to ampicillin alone.) Verify against a children's formulary.

Dose adjustments

Renal

In severe renal impairment (creatinine clearance <10 ml/min) a reduction in dose or extension of dose interval should be considered. In dialysis, give an additional dose after the procedure.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

UK SPC: for meningitis, children's dosage is 150 mg/kg daily IV in divided doses. General paediatric guidance: half adult routine dosage for children under 10 years. All dosages are a guide only and may be increased in severe infections. (Note: US FDA fallback label is for ampicillin/sulbactam combination — 300 mg/kg/day of the combination in children ≥1 year — not directly comparable to ampicillin alone.) Verify against a children's formulary.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • History of hypersensitivity to beta-lactam antibiotics (e.g. ampicillin, penicillins, cephalosporins)

Side effects

  • Skin rash, pruritus and urticaria (occasional; higher incidence in infectious mononucleosis and lymphoid leukaemia)
  • Nausea, vomiting and diarrhoea
  • Anaphylaxis (rare)
  • Interstitial nephritis (rare)
  • Haematological effects — transient leucopenia, thrombocytopenia and haemolytic anaemia (rare)

Interactions

  • Aminoglycosides — do not mix in the same syringe/IV container/giving set; loss of aminoglycoside activity can occur
  • Bacteriostatic drugs — may interfere with the bactericidal action of ampicillin
  • Oral contraceptives — ampicillin may reduce their efficacy; warn patients
  • Probenecid — decreases renal tubular secretion of ampicillin, increasing and prolonging blood levels
  • Allopurinol — concurrent use can increase the likelihood of allergic skin reactions

Clinical monograph

How it works

It inhibits bacterial cell wall synthesis by binding penicillin-binding proteins, leading to bacterial lysis.

Prescribing in practice

  • It is contraindicated in patients with penicillin hypersensitivity, who are at risk of anaphylaxis.
  • A maculopapular rash is common if given in glandular fever (infectious mononucleosis) and it should be avoided in this setting.
  • Many common organisms produce beta-lactamases conferring resistance, so therapy should be guided by susceptibility where possible.

Monitoring

Monitor for hypersensitivity reactions and clinical response, and review renal and hepatic function with prolonged or high-exposure treatment.

Counselling the patient

  • Report any rash, swelling or breathing difficulty, which may indicate allergy.
  • Complete the full prescribed course even if you feel better.
  • Tell your prescriber if you have ever reacted to a penicillin.

Evidence & guidelines

Ampicillin and related aminopenicillins are long-established agents with well-defined roles in UK antimicrobial guidance.

Reference: BSAC Endocarditis Guidelines (2012 updated); NICE NG51 (Meningitis); PHE/UKHSA antibiotic guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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