phenoxymethylpenicillin

penicillin antibiotic· Brands: Pen V, V-Cillin K, VeetidsPO

Mechanism of action

Phenoxymethylpenicillin is a beta-lactam antibiotic. It inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins, disrupting peptidoglycan cross-linking and causing cell lysis.

Pharmacokinetics

Acid-stable and well absorbed orally. Peak plasma concentrations occur 1-2 hours after dosing. Protein binding is about 80%. Metabolised to a minor extent, mainly excreted unchanged in urine. Food reduces absorption, so take on an empty stomach.

Indications & dosing

Streptococcal pharyngitis/tonsillitis

Complete 10-day course to prevent rheumatic fever.

adult · PO: 500 mg Q6H · Complete 10-day course to prevent rheumatic fever.

Streptococcal pharyngitis/tonsillitis

Weight-based dosing: 15 mg/kg/dose; use 250 mg for children weighing 15-30 kg.

pediatric · PO: 250 mg Q6H · Weight-based dosing: 15 mg/kg/dose; use 250 mg for children weighing 15-30 kg.

Rheumatic fever prophylaxis

Long-term prophylaxis; alternatively 500 mg once daily.

adult · PO: 250 mg BD · Long-term prophylaxis; alternatively 500 mg once daily.

Pneumococcal infections

For mild community-acquired pneumonia or other pneumococcal infections; severe infections require intravenous therapy.

adult · PO: 500 mg Q6H · For mild community-acquired pneumonia or other pneumococcal infections; severe infections require intravenous therapy.

Contraindications & precautions

Hypersensitivity to penicillins · Includes history of anaphylaxis, angioedema, or other severe reactions.
Hypersensitivity to cephalosporins · Potential cross-reactivity; avoid if previous severe reaction to any beta-lactam.
Ask about a history of penicillin, cephalosporin, or other beta-lactam allergy before prescribing.
Use with caution in patients with asthma, eczema, or allergic diathesis.
Avoid in infectious mononucleosis because of the high risk of rash.
Dose adjustment may be necessary in severe renal impairment.
Administer on an empty stomach, 30-60 minutes before food, for optimal absorption.
Monitor for signs of superinfection or C. difficile-associated diarrhoea during prolonged therapy.

Adverse effects

Gastrointestinal disturbances (nausea, vomiting, diarrhoea)
Rash (maculopapular)
Oral candidiasis
Anaphylaxisserious
Angioedemaserious
Clostridioides difficile-associated diarrhoeaserious
Blood dyscrasias (e.g., neutropenia, thrombocytopenia)serious
Drug-induced liver injuryserious
Convulsionsserious
Stevens-Johnson syndrome / toxic epidermal necrolysisserious

Renal & hepatic adjustment

eGFR 30+: No dose adjustment required.
eGFR 10–29: Consider reducing dose to half the usual dose.
eGFR 0–9: Consider halving the dose or extending the dosing interval (e.g., every 12 hours).

Monitoring, pregnancy & toxicity

Clinical response to infection · At regular intervals during therapy
Signs of hypersensitivity (e.g., rash, urticaria, anaphylaxis) · Throughout treatment; especially first dose
Renal function (serum creatinine, eGFR) · In patients with renal impairment or on prolonged therapy
Pregnancy: Penicillin V is generally considered safe in pregnancy; it is used when indicated. No known teratogenic effects.
Toxicity: Hypersensitivity reactions (e.g., rash, urticaria, drug fever, angioedema, anaphylaxis) · Stop drug, treat anaphylaxis with adrenaline (epinephrine), corticosteroids and antihistamines as appropriate.
Toxicity: Gastrointestinal effects (nausea, vomiting, diarrhoea) · Supportive measures; ensure adequate hydration.
Toxicity: Neurotoxicity (e.g., seizures, encephalopathy) in overdosage, especially with renal impairment · Discontinue drug, supportive care; consider haemodialysis to remove the drug.

Clinical notes

Used for streptococcal infections, otitis media, sinusitis, and prophylaxis of rheumatic fever. Not effective against beta-lactamase-producing organisms. Give on an empty stomach. Allergic cross-reactivity with cephalosporins. Check renal function in severe impairment.

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BNF; local formulary