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Penicillins

Benzylpenicillin

Also sold as: Crystapen

Prescription neededPenicillins

Comes as:Injection

Usual adult dose

Penicillins

Benzylpenicillin

Also sold as: Crystapen

Prescription neededPenicillins

Comes as:Injection

Usual adult dose

Dose is set by your doctor. Given by injection into a vein or muscle in hospital, several times a day, for serious infections such as pneumonia or meningitis.

Your doctor may give you a different dose. Children's doses depend on weight.

Side effects

Common

pain at the injection site
diarrhoea
mild skin rash

Serious — get help

Stop taking it and see a doctor straight away if you notice:

severe allergic reaction (swelling of face or throat
difficulty breathing)
seizures with very high doses

Do not take it, or take care, if

Allergy to penicillin or any penicillin-type antibiotic
Severe kidney disease (dose must be lowered)
Epilepsy (use with caution at high doses)

Interactions

Medicines that can react with this one.

Moderate1 medicineTake together only with care. Ask your doctor or pharmacist.

Methotrexate
Penicillins can reduce methotrexate clearance and raise its toxicity.

Pregnancy

Category B

No risk seen in animal studies, but there are few studies in pregnant women. Usually considered safe when needed.

Generic alternatives

Similar medicines your doctor or pharmacist may offer instead.

Ampicillin
Ceftriaxone

Check with my other medicines

Always follow your doctor or pharmacistThis page is general information, not a prescription. Do not start, stop or change a medicine on your own.