Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Narrow-spectrum penicillin (Penicillin V)

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.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses 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.

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. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways