Benzathine penicillin

Sounds like 'ben-zah-theen pen-ih-sil-in'

Key points about benzathine penicillin

  • Benzathine penicillin is an antibiotic used to treat bacterial infections such as rheumatic fever and syphilis.
  • Benzathine penicillin is also called Bicillin LA.
  • Find out how it is given and possible side effects.
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Benzathine penicillin (also called Bicillin LA) is an antibiotic used to treat bacterial infections such as rheumatic fever and syphilis. It is also given to prevent conditions like rheumatic fever and poststreptococcal glomerulonephritis (a form of kidney inflammation).

Benzathine penicillin works by killing or stopping the growth of bacteria (bugs). It belongs to a group of antibiotics called penicillins. Like all antibiotics, benzathine penicillin is not effective against infections caused by viruses. Benzathine penicillin is available as an injection that is given into a muscle. 

A doctor or a nurse will give you this medicine. Tell them if you have ever had an allergic reaction to penicillin or any other medicine.
  • Injection site: Benzathine penicillin is given by injecting it into a large muscle in your buttock (bottom) in adults and older children, or in the thigh (infants and small children). This is called an intramuscular injection.
  • Pain relief: Benzathine penicillin is sometimes given with a local anaesthetic to relieve discomfort during the injection. If you have allergies to local anaesthetics tell your doctor or nurse. 
  • Number of doses: Some people may need 2 doses, which is given as 1 injection into each buttock at the same visit. Some people only need to have benzathine penicillin once, but others will need to come back for more doses every few weeks, or complete a course of treatment. Ask your doctor or nurse what the plan is for you and your condition. 
  • After your injection: After receiving your injection, you will be asked to wait in the clinic for 15 minutes. If you have any reaction following treatment (eg, a rash, itchiness or breathing difficulties), please tell a staff member immediately.

Like all medicines, benzathine penicillin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Pain, redness, swelling or soreness at the injection site 
  • Place a cold, wet cloth or ice pack where the injection was given. Leave it on for a short time.
  • Tell your doctor or nurse if troublesome.
  • Fever, chills, headache or fatigue
  • This may occur within a few hours after treatment of early syphilis, although not everyone will have this reaction.
  • Do not be alarmed – this is not an allergic response and usually ends in 24 hours.
  • You can take paracetamol or ibuprofen to help relieve symptoms.
  • This reaction rarely occurs after treatment of late syphilis.
  • Tell your doctor if troublesome.
  • Diarrhoea (runny poo)
  • Nausea (feeling sick)
  • This should settle after a few days.
  • Tell your doctor if ongoing and troublesome.
  • Signs of an allergic reaction such as skin rash, itching, swelling of your lips, face and mouth, or difficulty breathing
  • A trained healthcare professional will observe you for at least 15 minutes after being given the injection.
  • If these symptoms develop after that, go straight to the emergency department at your nearest hospital.

Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)


  1. Benzathine penicillin(external link) NZ Formulary
  2. Stop sore throats(external link) Health New Zealand | Te Whatu Ora

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

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