Benzylpenicillin
Bensylpenicillin Viatris · Benzylpenicillin Panpharma
First-line treatment for community-acquired pneumonia and erysipelas, and the foundation of the narrow-spectrum antibiotic tradition. Pneumococci, streptococci, and most oral anaerobes remain sensitive, and the resistance situation is favourable compared to almost all other countries. Time-dependent killing means that the dosing interval matters more than the size of any individual dose — four doses are preferable to two large ones.
Anaphylaxis occurs, though rarely. Always ask about previous penicillin reactions and distinguish true type I allergy from the common non-specific rashes — incorrect allergy labelling drives the patient toward broad-spectrum alternatives with worse outcomes.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Community-acquired pneumonia | 1–3 g iv × 3 | 3 g × 3 if CRB-65 score 2 or higher |
| Erysipelas | 1–3 g iv × 3 | switch to phenoxymethylpenicillin orally when clinical improvement is evident |
| Bacterial meningitis | 3 g iv × 4 | high dose required for CNS penetration; given with corticosteroids |
| Endocarditis, viridans streptococci | 3 g iv × 4–6 | according to culture results and MIC, often in combination |
| Suspected pneumococcal sepsis | 3 g iv × 4 | given immediately, within one hour of sepsis alert |
Full dose down to eGFR 30 ml/min. At eGFR 10–30 ml/min give normal single dose but extended interval (every 8 to every 12 hours). At eGFR below 10 ml/min and on dialysis the daily dose is further reduced. High doses (12 g or more daily) in renal impairment carry a risk of penicillin encephalopathy with myoclonus and seizures — the most common dose-related complication.
No dose adjustment in hepatic failure.
Children 1–12 years 150 mg/kg/day divided into 3–4 doses; infants 1 month to 1 year 100 mg/kg/day. In meningitis a higher dose is used, 200–300 mg/kg/day.
Avoid as sole empirical therapy in septic shock with unknown focus, nosocomial pneumonia, and abdominal or urinary tract focus — Gram-negative coverage is absent. Also avoid relying on a documented penicillin allergy without investigating what actually happened; the vast majority of allergy labels do not hold up on investigation.
Pharmacokinetics
- t½
- 30–50 minutes
- BIOAVAIL.
- Parenteral only
- PROTEIN BINDING
- Approximately 65 %
- METABOLISM
- Minimal hepatic
- EXCRETION
- Renal, approximately 70 % within 6 hours
- CNS PENETRATION
- Low, increases with meningeal inflammation
- CONVERSION
- 1 g ≈ 1.6 million IU
- PK/PD
- Time-dependent, T > MIC