Also called penicillin G
Benzylpenicillin
An injectable penicillin antibiotic used in hospital to treat serious bacterial infections.
What is Benzylpenicillin?
Benzylpenicillin, also called penicillin G, is a penicillin antibiotic given by injection to treat serious bacterial infections such as meningitis, severe chest, heart-valve and blood infections, and certain other infections. It works by killing the bacteria responsible. The most important safety point is penicillin allergy: in people allergic to penicillin it can cause a serious, sometimes life-threatening allergic reaction, so allergy must always be checked first. Because it is not well absorbed from the gut, it is given into a vein or muscle, usually in hospital.
Education and reference only. This is a plain-language guide to Benzylpenicillin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Benzylpenicillin, also known as penicillin G, is one of the original penicillin antibiotics and is still important for treating a number of serious bacterial infections. It is used in hospital for conditions such as meningitis, severe infections of the chest, heart valves or bloodstream, and certain other specific infections. Because it is broken down by stomach acid and poorly absorbed if swallowed, it is given by injection — into a vein or a muscle — rather than as a tablet. It is prescribed and given by healthcare professionals, usually in hospital.
How it works
Benzylpenicillin works by stopping bacteria from building their protective cell walls. Without a sound cell wall the bacteria break apart and die, which clears the infection. It is particularly effective against several bacteria that cause serious illness. Because it is destroyed by stomach acid and poorly absorbed from the gut, it has to be given by injection so that enough of it reaches the bloodstream to fight the infection. Giving it directly into a vein also allows high levels to be reached quickly, which matters in severe infections.
Company & origin
Originated / developed by: Various manufacturers.
An injectable penicillin antibiotic used in UK hospitals to treat serious bacterial infections, given into a vein or muscle.
Practical use
How to take Benzylpenicillin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by injection into a vein or muscle by healthcare professionals, usually in hospital.
- Always tell the team about any allergy to penicillin or other antibiotics before it is given.
- Tell staff straight away about any rash, swelling, wheeze or faintness during treatment.
- It is usually given several times a day to keep enough antibiotic in the body.
- The full course is completed even if you feel better, to clear the infection fully.
Weighing it up
Advantages & disadvantages of Benzylpenicillin
Advantages
- A highly effective treatment for several serious bacterial infections.
- Works quickly when given into a vein, which matters in severe illness.
- A long-established antibiotic with a well-understood role in serious infections.
Disadvantages
- Can cause serious allergic reactions in people allergic to penicillin.
- Must be given by injection, usually in hospital, rather than as a tablet.
- Needs to be given several times a day because it does not last long in the body.
Practical use
Good to know
The single most important point with benzylpenicillin is allergy. People who are allergic to penicillin can have a serious and sometimes life-threatening allergic reaction (anaphylaxis), so it is essential to tell the team about any penicillin or other drug allergy before it is given, and any rash, swelling, wheeze or faintness during treatment is treated as an emergency. Some people also have allergies to related antibiotics such as cephalosporins. Because it is given by injection in hospital, the team monitors how you respond. In serious infections such as meningitis it is sometimes started very quickly, including before reaching hospital, because early treatment saves lives. It is usually given several times a day, and the full course is important to clear the infection and reduce the chance of resistance.
Who should not take it / use with caution
- People who are allergic to penicillin must not be given it because of the risk of a serious allergic reaction.
- It is used with caution in people with allergies to related antibiotics such as cephalosporins.
- The dose is adjusted carefully in people with kidney problems, under medical supervision.
Monitoring
- Watching closely for any allergic reaction, especially when it is first given.
- Checking that the infection is responding to treatment.
- Keeping an eye on kidney function and, with high amounts, the nervous system.
Side effects
- Allergic reactions, ranging from a rash to serious, life-threatening anaphylaxis.
- Diarrhoea or stomach upset, including, rarely, a gut infection caused by disturbed bowel bacteria.
- Soreness or irritation where the injection is given.
- Rarely, with very high amounts, effects on the nervous system such as confusion or fits, watched for in hospital.
Key interactions
- It can interact with some other medicines, so the team is told everything you take.
- Probenecid, a gout medicine, can raise penicillin levels and is sometimes used deliberately.
- Tell staff about all your medicines so treatment can be given safely.
Available as: A powder made up into a solution for injection into a vein or muscle.
Answers
Benzylpenicillin: frequently asked questions
What is benzylpenicillin used for?
It is an injectable penicillin antibiotic used to treat serious bacterial infections such as meningitis and severe chest, heart-valve and bloodstream infections, usually in hospital.
Why is it given by injection?
It is destroyed by stomach acid and poorly absorbed if swallowed, so it is given into a vein or muscle to make sure enough reaches the bloodstream to fight the infection.
What if I am allergic to penicillin?
If you are allergic to penicillin you must not be given it, as it can cause a serious, sometimes life-threatening reaction; always tell the team about any allergy before treatment.
Is it the same as penicillin G?
Yes. Benzylpenicillin is also called penicillin G; they are two names for the same antibiotic.
Why is it given several times a day?
It does not stay in the body for long, so it is given several times a day to keep enough antibiotic present to keep working against the infection.
The wider class
About Penicillin antibiotic (injectable)
Benzylpenicillin belongs to the penicillin antibiotic (injectable) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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