Chlamydia treatment: why 7 days? | HAP.GENT

Chlamydia: why a seven-day course of antibiotics?

“Doctor, last time I was given two pills to take together. Now I have to take a tablet every morning and evening for seven days. Has chlamydia become harder to treat?”

Imagine this fictional situation: a patient who has experienced discomfort when passing urine receives the results of an STI test. The test is positive for chlamydia. He remembers previously taking two tablets together and wonders why the prescription is different this time.

It is an understandable question. A different antibiotic is now usually prescribed. New research has helped clarify which treatment works most reliably, particularly when the bacteria are also present in the rectum.

What were those two pills?

They were usually two 500 mg azithromycin tablets, taken together as a single 1 gram dose. This convenient, one-off treatment was widely used for uncomplicated chlamydia. Doxycycline was already available as a treatment at that time too.

For men and non-pregnant women, Belgian recommendations now favour doxycycline: 100 mg twice a day for seven days. If you have 100 mg tablets, that means one tablet in the morning and one in the evening, fourteen in total. These are two different medicines, each with its own dosage—not the same medicine suddenly needing a longer course. [1,2]

Why is doxycycline preferred?

The main difference is seen in chlamydia affecting the rectum, the final part of the bowel. At this site, a course of doxycycline works more reliably than a single dose of azithromycin.

In a randomised trial involving men who have sex with men, the rectal infection cleared in all 70 participants with an available follow-up result after doxycycline, compared with 48 out of 65 after azithromycin. These figures apply to this particular study group. They do not mean that azithromycin is equally likely to be unsuccessful in every type of chlamydia infection, but they help explain the change in preferred treatment. [3]

A rectal infection does not always cause symptoms. In women, it can occur alongside a genital infection, even when they do not report having anal sex. Doxycycline then treats both sites. [1,4]

Has chlamydia become resistant to antibiotics?

That is not an accurate general explanation. A treatment can work less well at a particular site in the body without this proving that the bacteria have become resistant.

Responsible antibiotic use does play a role, however. Antibiotics also affect other bacteria in the body. Azithromycin can select for resistance in those other bacteria. Belgian recommendations therefore consider both effectiveness against chlamydia and the risk of resistance in other bacteria. [1,2]

Does this mean my previous treatment did not work?

A change in recommendations does not mean that everyone who previously received azithromycin was inadequately treated. This medicine can cure chlamydia and still has a place in treatment.

Having received it in the past is not, by itself, a reason to take antibiotics again now. Discuss any new symptoms, possible exposure or concerns about previous treatment with your GP. [1,4]

How should you take doxycycline?

Take your tablets at regular times, for example in the morning and evening, and complete the full prescribed course, even if your symptoms improve quickly. If you are unable to do this or experience troublesome side effects, contact your doctor or pharmacist.

Swallow the tablets with a full glass of water while sitting or standing upright. Do not take them just before lying down: doxycycline can irritate the oesophagus, the tube connecting your mouth to your stomach.

Leave a gap of several hours between doxycycline and iron, calcium or magnesium supplements, as well as certain medicines for heartburn. Ask your pharmacist what interval is needed for the products you take.

Doxycycline can make your skin more sensitive to sunlight, so avoid sunbeds and protect yourself from the sun. [5]

Are there any exceptions?

Yes. During pregnancy, a single 1 gram dose of azithromycin remains the first choice. Your doctor may also choose azithromycin if you are breastfeeding or if doxycycline is unsuitable or not tolerated.

Before starting treatment, tell your doctor if you are pregnant, could be pregnant or are breastfeeding, and mention any other medicines you take. [1,6]

The seven-day course applies to uncomplicated chlamydia. Conditions such as pelvic inflammatory disease, epididymitis or the particular type of chlamydia infection known as LGV require a different treatment approach. [1]

When can you have sex again?

Avoid sexual contact during treatment. With doxycycline, wait until you have completed the full seven-day course and any symptoms have resolved. After a single dose of azithromycin, wait at least seven days.

Also wait until your partner or partners have completed any necessary treatment. This helps reduce onward transmission and reinfection. [4]

Let recent sexual partners know that you have chlamydia. They may have the infection without symptoms and need advice about testing and possible treatment. Your GP can discuss which partners to notify and how to approach the conversation. Do not share your antibiotics with anyone else. [2,7]

Do you need another test afterwards?

After an uncomplicated infection has been correctly treated, a test to confirm that the infection has cleared is usually unnecessary. This test, known as a test of cure, is recommended during pregnancy, if treatment failure is suspected or if a non-standard treatment regimen was used.

When needed, it is carried out at least four weeks after the end of treatment. Testing too early can detect remaining traces of the bacteria and produce a misleading positive result. [4,8]

A later test following a new possible exposure or to check for reinfection serves a different purpose. Discuss with your GP what follow-up is appropriate for you. Testing for other STIs should also be part of that conversation. [1,4]

Contact your doctor again if symptoms persist. Seek prompt medical assessment if you develop a fever, significant lower abdominal pain, or pain and swelling in a testicle. These symptoms may indicate a complication or another condition. [1]

Do you have questions about your STI test or why your prescription has changed? At HAP.GENT GP practice in Ghent, you can discuss these concerns in confidence. Understanding your treatment helps you follow it correctly.

References

[1] BCFI. WOREL publishes a revised guideline on Chlamydia trachomatis. 19 June 2025. In Dutch.

[2] BCFI. Revised BAPCOC guide: changes concerning urogenital and ophthalmic infections. 1 July 2026. In Dutch.

[3] Dombrowski JC et al. Doxycycline Versus Azithromycin for the Treatment of Rectal Chlamydia in Men Who Have Sex With Men: A Randomized Controlled Trial. Clinical Infectious Diseases. 2021;73(5):824–831.

[4] CDC. Chlamydial Infections — STI Treatment Guidelines.

[5] BCFI. Tetracyclines and doxycycline — drug information. In Dutch.

[6] KCE. Management of STIs in primary care — Treatment. In Dutch.

[7] Sciensano. Sexually transmitted infections. In Dutch.

[8] KCE. Management of STIs in primary care — Test of cure. In Dutch.