Antibiotic — Tonsillitis / Pharyngitis
Pregnancy: Safe in pregnancy — well-established safety record
Phenoxymethylpenicillin (Penicillin V)
Brand names: Penicillin VK
Adult dose
Dose: 500 mg
Route: Oral
Frequency: Four times daily for 5–10 days
Max: 4 g/day
First-line antibiotic for group A streptococcal (GAS) tonsillitis/pharyngitis (FeverPAIN score ≥4 or Centor ≥3). NICE guidance: offer delayed or immediate antibiotic prescription based on severity. 10-day course eradicates GAS more reliably than 5-day. Take on empty stomach for best absorption.
Paediatric dose
Dose: 12.5 mg/kg mg/kg
Route: Oral
Frequency: Four times daily for 5–10 days
Max: 500 mg per dose
BNFc: 1 month–1 year 62.5 mg QDS; 1–5 years 125 mg QDS; 6–11 years 250 mg QDS; 12–17 years 500 mg QDS. Liquid formulation available.
Dose adjustments
Renal
No dose adjustment required
Hepatic
No dose adjustment required
Paediatric weight-based calculator
BNFc: 1 month–1 year 62.5 mg QDS; 1–5 years 125 mg QDS; 6–11 years 250 mg QDS; 12–17 years 500 mg QDS. Liquid formulation available.
Clinical pearls
- NICE NG84 (sore throat): use FeverPAIN score — score ≥4 → immediate antibiotic; score 2–3 → delayed prescription; score 0–1 → no antibiotic
- Penicillin V is preferred over amoxicillin for GAS pharyngitis — narrower spectrum, less risk of rash in EBV infection
- If amoxicillin given in EBV (infectious mononucleosis) without knowing diagnosis — can cause florid maculopapular rash in ~90% of patients
- Clarithromycin or erythromycin for penicillin allergy; cefalexin (non-anaphylaxis allergy) is an alternative
- Peritonsillar abscess (quinsy): IV benzylpenicillin + metronidazole; drain + IV antibiotics, then oral step-down
Contraindications
- Penicillin hypersensitivity
Side effects
- GI disturbance (nausea, diarrhoea)
- Rash
- Anaphylaxis (rare)
Interactions
- Methotrexate — increased methotrexate toxicity (reduced renal excretion)
- Warfarin — may increase INR (monitor)
Monitoring
- Symptom response (48–72 hours)
- Signs of quinsy (peritonsillar abscess)
Reference: BNFc; BNF 90; BNFc; NICE NG84 (Sore Throat — Antibiotic Prescribing 2018); SIGN 117. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators