Doxy-PEP (doxycycline post-exposure prophylaxis)

Doxy-PEP is an oral dose of an antibiotic called doxycycline, which is taken within 72 hours (3 days) of having sex (oral, anal, or vaginal) to protect against syphilis and chlamydia. Doxycycline is a safe and common medication used to treat certain infections, control acne, and prevent malaria. It does not work against viral infections such as HIV or herpes.

Decision aid for consumers

This decision-aid can help you decide whether to use antibiotics after sex to reduce your risk of contracting syphilis and chlamydia. Consider taking this information with you when you see your doctor to help make a shared and informed decision about whether Doxy-PEP is right for you.

Doxy-PEP is most likely to benefit people at higher risk of syphilis, such as gay, bisexual, and other men who have sex with men, and transgender women, especially with recent syphilis or recent sexually transmissible infections (STI). It may also benefit others who want to reduce their risk of STI, including people taking HIV pre-exposure prophylaxis (PrEP) and sex workers after a condom break.

Doxy-PEP reduces the risk of syphilis (by 70-80%) and chlamydia (by 70-90%). It is unlikely to be effective against gonorrhoea due to antibiotic resistance, so it is still important to have a regular STI test.

Potential benefits

  • Prevents syphilis and chlamydia infection.
  • Reduces the spread of STI within your sexual networks.
  • Provides added protection alongside condoms and STI testing.

Potential risks*

  • Common but non-serious side effects including nausea, vomiting and diarrhoea.
  • Your skin may become more sensitive to sunlight, causing a rash or sunburn.
  • Rare but serious reactions such as allergies, oesophageal ulcers or liver damage.
  • If used after 18 weeks of pregnancy, it can cause bone and teeth defects in your baby.
  • May contribute to antibiotic resistance in your body, or in the community, and reduce your future treatment options for STI and other infections. This may be important for people with weakened immune systems or chronic diseases, as they are more likely to have frequent or severe bacterial infections.
  • May reduce the effectiveness of some contraceptive pills (The Pill). If you are taking The Pill, ask your doctor if you need to use another form of contraception while you take Doxy-PEP.

*For more safety information see Safety information about doxycycline.

Doxy-PEP is one approach among several for preventing STI. An open conversation with your doctor can help determine if Doxy-PEP is suitable for you based on your specific needs.

Discuss with your doctor:

  • your personal STI risk factors
  • the benefits and potential risks of Doxy-PEP for your situationdosing instructions and what to expect if Doxy-PEP is recommended
  • taking HIV pre-exposure prophylaxis (PrEP) if you are at risk of HIV.

If you have any concerns about taking doxycycline or experience any adverse effects from this medicine, speak with your doctor or pharmacist. If you decide to take Doxy-PEP, it is recommended to visit your doctor after three to six months to assess if you need to keep using it.

Using antibiotics causes bacteria to develop resistance, making them less effective for treating infections. Antibiotic resistance is a problem throughout the world and is a major threat to human health. For STI, this is an issue for gonorrhoea. Widespread use of Doxy-PEP may increase resistant gonorrhoea strains in the community. It is important to weigh these concerns against the benefits of Doxy-PEP, particularly in preventing the serious health complications associated with syphilis.

Using Doxy-PEP

  • Take two 100 mg doxycycline tablets or capsules once within 72-hours (three days) after having sex (oral, anal, or vaginal sex). See the image below.
  • Take doxycycline with food and a full glass of water to prevent stomach upset. Do not lie down for at least an hour after swallowing the tablets, to avoid irritation of your food pipe.
  • Do not take Doxy-PEP more than once every three days.
  • Do not take antacids, iron, calcium, zinc or fibre supplements within two hours of doxycycline as they may interfere with its absorption.
  • Apply sunscreen when out in the sun to avoid sunburn.

When to take Doxy-PEP

  • Do not take doxycycline if you have a known tetracycline allergy - the class of antibiotics that doxycycline belongs to.
  • Do not take doxycycline after the 18th week of pregnancy.
  • Discuss the risks and benefits of taking doxycycline while breastfeeding with your doctor. Short courses (7-10 days) are considered safe.
  • Consult your doctor or pharmacist about possible interactions if you are taking any of the following:
    • vitamin A preparations and medicines for skin problems (e.g., isotretinoin, etretinate)
    • Warfarin, a medicine used to prevent blood clotting
    • penicillins, another group of antibiotics (e.g., amoxicillin)
    • epilepsy medicines (e.g., phenytoin, carbamazepine, phenobarbitone)
    • contraceptive pills (The Pill), as doxycycline may decrease their effectiveness, requiring additional contraception.

  • Getting tested regularly and treating any STI promptly
  • Using condoms consistently and correctly.

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