Penicillin G (parenteral) Pregnancy: Taken by a large number of pregnant women and women of childbearing age without an increase in malformations or other harmful effects on the foetus observed. Actively transported into milk in animals; trace amounts of other penicillins detected in human milk.

Benzylpenicillin sodium

Brand names: Crystapen

Benzylpenicillin sodium is the soluble sodium salt of penicillin G used for intravenous or intramuscular administration in serious susceptible infections such as streptococcal sepsis, endocarditis, pneumococcal and meningococcal disease.

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: 600 to 3,600 mg (1 to 6 mega units) daily, divided into 4 to 6 doses, depending on the indication

Route: Intramuscular or intravenous

Frequency: In 4 to 6 divided doses daily

Max: Up to 14.4 g/day (24 mega units) in divided doses IV in serious infections such as adult meningitis; up to 43.2 g/day (72 mega units) may be necessary in rapidly spreading gas gangrene

Higher doses by IV route in serious infection. Bacterial endocarditis: 7.2 to 12 g (12 to 20 mega units) or more daily in divided doses IV, often by infusion. IV doses in excess of 1.2 g (2 mega units) given slowly, at least 1 minute per 300 mg (0.5 mega unit). Meningococcal disease (adults and children over 12 years): 2.4 g every 4 hours. Suspected meningococcal disease before hospital transfer: adults and children over 10 years 1,200 mg IV/IM (children 1-9 years 600 mg; children under 1 year 300 mg). Group B streptococcal prophylaxis of newborn: mother given 3 g (5 mega units) loading dose, then 1.5 g (2.5 mega units) every 4 hours until delivery. High doses may cause hypernatraemia and hypokalaemia unless sodium content is taken into account.

Paediatric dose

Dose: 100 mg/kg

Route: Intramuscular or intravenous

Frequency: In 4 divided doses per day

Max: Not exceeding 4 g/day

Children aged 1 month to 12 years: 100 mg/kg/day in 4 divided doses, not exceeding 4 g/day. Infants 1-4 weeks: 75 mg/kg/day in 3 divided doses. Newborn infants: 50 mg/kg/day in 2 divided doses. Meningococcal disease children 1 month to 12 years: 180-300 mg/kg/day in 4-6 divided doses (not exceeding 12 g/day); infants 1-4 weeks 150 mg/kg/day in 3 divided doses; newborn infants 100 mg/kg/day in 2 divided doses. Premature babies and neonates: dosing not more frequent than every 8-12 hours; IV treatment preferred over IM. Verify paediatric doses against a children's formulary.

Dose adjustments

Renal

In renal insufficiency: for 0.6-1.2 g (1-2 mega units) doses, dosing interval no more frequent than every 8-10 hours. For high doses (e.g. 14.4 g/24 mega units for meningitis), adjust dose and interval by creatinine clearance per SPC schedule. If haemodialysis required, give an additional 300 mg (0.5 mega units) every 6 hours during the procedure. Reduce to 300 mg 8-hourly if advanced liver disease is associated with severe renal failure.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Verify in a children's formulary

Contraindications

Allergy to penicillins
Hypersensitivity to any ingredient of the preparation
Cross allergy to other beta-lactams such as cephalosporins should be taken into account

Side effects

Hypersensitivity: rashes (all types), fever, serum sickness (common)
Anaphylactic reactions (rare)
Jarisch-Herxheimer reaction when treating syphilis/neurosyphilis (very common in that setting)
Granulocytopenia/neutropenia, agranulocytosis, leucopenia with prolonged high doses (rare)
CNS toxicity including convulsions with massive doses (over 60 g/day) or severe renal impairment (rare); interstitial nephritis

Clinical monograph

How it works

The penicillin moiety binds penicillin-binding proteins to inhibit bacterial cell-wall synthesis and is bactericidal against susceptible organisms; the sodium salt provides a rapidly soluble form suitable for injection.

Prescribing in practice

Contraindicated in penicillin hypersensitivity; cross-reactivity with other beta-lactams and risk of anaphylaxis mean allergy status must be checked before administration.
Each formulation carries a sodium load that is relevant at high doses or in patients with cardiac or renal impairment requiring sodium restriction.
High plasma concentrations, particularly in renal impairment, can precipitate seizures, so dosing must account for renal function.

Monitoring

Monitor renal function, serum electrolytes including sodium and potassium, and for neurological toxicity during high-dose or prolonged courses.

Counselling the patient

This is a penicillin given by drip or injection for serious infection.
Report rash, facial swelling or difficulty breathing without delay.
Inform staff of any previous reaction to penicillin.

Evidence & guidelines

It is a long-established standard parenteral penicillin for susceptible Gram-positive and meningococcal infections in national guidance.

Reference: NICE NG52; UKHSA; BSAC; 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