Penicillin G Injectable: Dosing and Precautions
Short-acting benzylpenicillin guidance for diphtheria, severe leptospirosis, neurosyphilis, and congenital syphilis.
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Source reviewed
June 2025
Guide category
Injectable drugs
Safety boundary
Prescription medicine information for clinician-guided use.
Kenza Health Hub presents this medicine page as structured health education. Check dose, route, interactions, pregnancy or breast-feeding considerations, and local protocol with a qualified clinician or pharmacist. Read our medical editorial policy.
Therapeutic action
Short-acting penicillin antibacterial.
Indications
- Diphtheria, when oral treatment is not possible.
- Severe leptospirosis and neurosyphilis.
- Congenital syphilis when the neonate has clinical signs or the mother did not receive adequate treatment.
Forms and strengths, route of administration
- Powder for injection in 1 MIU and 5 MIU vials.
- For IM injection, slow IV injection through an infusion tube, or IV infusion in 0.9% sodium chloride or 5% glucose.
Dose
Diphtheria
- Child: 25,000 IU/kg by IM or IV injection every 6 hours, maximum 1 MIU.
- Adult: 1 MIU by IM or IV injection every 6 hours.
Severe leptospirosis
- Child: 50,000 IU/kg by IV injection every 6 hours, maximum 2 MIU.
- Adult: 1 to 2 MIU by IV injection every 6 hours.
Neurosyphilis
- Adult: 2 to 4 MIU by IV injection every 4 hours.
Congenital syphilis
- 50,000 IU/kg by IV injection every 12 hours from D1 to D7.
- Then 50,000 IU/kg by IV injection every 8 hours from D8 to D10.
Duration
- Diphtheria: change to oral treatment as soon as the patient can swallow, to complete 14 days.
- Severe leptospirosis: 7 days.
- Neurosyphilis: 14 days.
- Congenital syphilis: 10 days.
Contra-indications, adverse effects, precautions
- Once reconstituted, suspension must be used immediately.
- Do not administer to penicillin-allergic patients.
- Administer with caution to patients allergic to cephalosporins and to patients with renal impairment.
- May cause gastrointestinal disturbances, pain at injection site, anaemia, allergic reactions, Jarisch-Herxheimer reaction, and convulsions in the event of rapid IV injection, high dosages, or renal impairment.
- Do not combine with methotrexate.
- Pregnancy and breast-feeding: no contra-indication.
- Do not confuse short-acting benzylpenicillin with long-acting penicillins.
- Do not mix with other drugs in the same syringe or infusion.
Source
MSF Essential drugs practical guidelines (January 2026)
This page combines source-derived medicine reference sections with Kenza editorial context, while leaving out the Storage and Remarks sections from the source batch.
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