💊 Broad-spectrum penicillin antibiotic.
🦠 Belongs to the beta-lactam class, related to amoxicillin.
⚠️ Less commonly used now due to resistance, but still important for some indications (e.g. Listeria).

⚡ Mechanism of Action

Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs).
Blocks final transpeptidation step → cell wall weakening and lysis.
Bactericidal, time-dependent killing.

🧬 Activity

Some Escherichia coli strains.
Proteus mirabilis, Shigella, Salmonella.
Haemophilus influenzae (non–β-lactamase producers).
Some Enterococci.
⚠️ High rates of resistance among Gram-negative organisms in UK practice.

🩺 Indications

🌬️ Exacerbation of COPD.
🦠 Invasive salmonellosis.
❤️ Endocarditis (often combined with gentamicin).
🧠 Listeria meningitis (drug of choice, often with gentamicin).
💧 Urinary tract infections.
👂 ENT infections – otitis media, sinusitis (though amoxicillin often preferred).

💊 Dosing – Ampicillin (verify with BNF/datasheet)

Indication	Details
🦠 Mild–Moderate Infection	Ampicillin • 250 mg – 1 g QDS • Route: PO / IV / IM
🔥 Severe Infection	Ampicillin • 2 g slow IV/IM every 4 h • Infuse with 100 mL 0.9% saline or 5% glucose over 30 min

🔄 Interactions

⬆️ Probenecid increases ampicillin levels (reduced renal clearance).
⬆️ Risk of methotrexate toxicity (displacement & ↓ renal clearance).
⬇️ May reduce efficacy of the oral contraceptive pill.

⚠️ Cautions

🌡️ Causes characteristic rash in patients with EBV/CMV (infectious mononucleosis, glandular fever).
📊 High risk of rash in patients with ALL/CLL.
💧 Dose adjustment in renal impairment (renally cleared drug).

🚫 Contraindications

⚠️ Penicillin allergy (risk of anaphylaxis).
Infectious mononucleosis (rash almost universal if given).
History of severe cholestatic jaundice/hepatic dysfunction associated with ampicillin.

💥 Side Effects

🌡️ Maculopapular rash (esp. in EBV/CMV, ALL/CLL).
🤢 GI upset: nausea, vomiting, diarrhoea.
🤧 Hypersensitivity reactions: urticaria, anaphylaxis (rare but serious).
🩸 Rare: haemolytic anaemia, thrombocytopenia, eosinophilia.
🦠 Candida overgrowth (oral/vaginal thrush) with prolonged use.

📑 References

BNF: Ampicillin
NICE Antimicrobial Guidance

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Ampicillin

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