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How effective is a penicillin injection for treating syphilis?

Syphilis is treated effectively by penicillin antibiotic injections or tablets (if you can’t have penicillin). The length of treatment depends on how long you’ve had the infection and the preferred treatment at all stages is penicillin. This is only available on prescription, so you’ll need to be tested for syphilis to get them. If you’re allergic to penicillin, your doctor may suggest another antibiotic or recommend penicillin desensitization.

When diagnosed and treated in its early stages, syphilis is easy to cure. If you are diagnosed with primary, secondary or early-stage latent syphilis (less than two years), the recommended treatment is a single injection of penicillin. If you’ve had syphilis for more than two years, you may need additional doses - usually 3 penicillin injections into your buttocks given at weekly intervals, or a 28 day course of antibiotic tablets if you can’t have penicillin.

More serious cases of syphilis that affect the brain are usually treated with daily penicillin injections given into your buttocks or a vein for 2 weeks, or a 28 day course of antibiotic tablets if you can’t have penicillin.

Follow-up blood tests will be recommended once treatment finishes to check that it has worked. Side effects of treatment can include flu like symptoms in 2 out of 5 people, and a risk of an allergic reaction to the penicillin injection. All sexual contact must be avoided until at least two weeks after your treatment has ended.

Pregnant women with syphilis can usually be safely treated with antibiotics. The treatment you need depends on how long you’ve had syphilis and how far along in your pregnancy you are.

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Dr Gillian Holdsworth headshot

This post was clinically reviewed by:
Dr Gillian Holdsworth Fettle's Managing Director, Medical Doctor and public health expert.

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