Narrow-spectrum penicillin (Penicillin V) Pregnancy: There are no or limited data in pregnant women; as a precautionary measure it is preferable to avoid use during pregnancy. Metabolites are excreted in human milk.

Phenoxymethylpenicillin

Phenoxymethylpenicillin (penicillin V) is an oral narrow-spectrum penicillin used for streptococcal infections such as tonsillitis, and for prophylaxis in rheumatic fever and after splenectomy.

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: 250 mg to 500 mg

Route: Oral

Frequency: Every 6 hours

Adults (including the elderly) and children over 12 years: 250 mg to 500 mg every six hours; dose and frequency depend on severity, site and expected pathogens. Take at least 30 minutes before or 2 hours after food (food slightly reduces absorption). Prophylaxis of rheumatic fever/chorea: 250 mg twice daily on a continuing basis. Prophylaxis of pneumococcal infection (e.g. asplenia, sickle cell disease): adults and children over 12 years 500 mg every 12 hours. Streptococcal infections should be treated for a minimum of 10 days. Paediatric doses are given by age band (infants up to 1 year 62.5 mg every 6 hours; 1-5 years 125 mg every 6 hours; 6-12 years 250 mg every 6 hours) rather than per kg. Reduce dosage if renal function is markedly impaired. 250 mg is approximately equivalent to 400,000 units.

Dose adjustments

Renal

Dosage should be reduced if renal function is markedly impaired.

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.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION The dosage of Penicillin V should be determined according to the sensitivity of the causative microorganisms and the severity of infection, and adjusted to the clinical response of the patient. The usual dosage recommendations for adults and children 12 years and over are as follows: Streptococcal Infections Mild to moderately severe - of the upper respiratory tract and including scarlet fever and erysipelas: 125 to 250 mg (200,000 to 400,000 units) every 6 to 8 hours for 10 days. Pneumococcal Infections Mild to moderately severe - of the respiratory tract, including otitis media: 250 to 500 mg (400,000 to 800,000 units) every 6 hours until the patient has been …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-10-15. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to penicillin or to any of the excipients
Use with caution in patients with known histories of allergy

Side effects

Nausea, vomiting, abdominal pain, diarrhoea (common)
Allergic skin reactions - urticarial/erythematous/morbilliform rash and pruritus (common)
Severe allergic reactions - angioedema, laryngeal oedema, anaphylaxis (rare)
Blood count changes - thrombocytopenia, neutropenia, leucopenia, eosinophilia, haemolytic anaemia (very rare)
Pseudomembranous colitis; CNS toxicity including convulsions (especially with high doses or severe renal impairment)

Interactions

Neomycin (aminoglycoside): reported to reduce absorption of phenoxymethylpenicillin
Anticoagulants: penicillins may interfere with anticoagulant control
Bacteriostatic antibiotics (chloramphenicol, erythromycin, tetracyclines): may antagonise the bactericidal activity - concomitant use not recommended
Probenecid and sulfinpyrazone: reduce excretion of penicillin (renal tubular competition)
Methotrexate: reduced methotrexate excretion, increasing risk of toxicity
Oral typhoid vaccine: may be inactivated if ingested concomitantly

Clinical monograph

How it works

It is a beta-lactam that inhibits bacterial cell-wall synthesis by binding penicillin-binding proteins, leading to bacterial cell death.

Prescribing in practice

Contraindicated in patients with penicillin allergy; check allergy status carefully before prescribing.
Absorption is improved on an empty stomach, so it is taken before food.
Its narrow spectrum makes it well suited to confirmed or suspected streptococcal infection and long-term prophylaxis.

Monitoring

Routine monitoring is not generally needed; for long-term prophylaxis, review adherence and ongoing need periodically.

Counselling the patient

Take doses on an empty stomach, ideally before food, and space them evenly through the day.
Complete the full course or continue prophylaxis as directed, and report any rash, swelling or breathing difficulty.

Evidence & guidelines

A long-established first-line choice for streptococcal pharyngitis and for splenectomy and rheumatic fever prophylaxis under NICE and local guidance.

Reference: NICE NG84/NG109; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways