Doxycycline - Effective Post-Exposure Prophylaxis following Unprotected Sex

Disclaimer: Not medical or professional advice. Always seek the advice of your physician.

A randomized, placebo-controlled clinical trial has been carried out in San Francisco and Seattle to assess the effectiveness of taking an antibiotic called doxycycline after unprotected sexual activity. Participants were assigned to receive a 200 mg doxycycline dose within three days after condomless sexual contact. The study was prematurely terminated due to the high efficacy of the drug in a specific group of patients.

Why Are Researchers Testing Antibiotics To Prevent STIs?

An estimated 250 million cases of sexually transmitted infections (STIs) occur worldwide each year. Since most of them remain asymptomatic throughout the course of infection, there are no accurate statistics on the incidence and prevalence rates. Some of these infections are caused by certain types of bacteria that resist the effects of antibiotics.

Chlamydia (Chlamydia trachomatis)

Chlamydia tops the list of most common sexually transmitted infections. Up to 50% of infected men and 80% of infected women have an asymptomatic infection without noticeable signs.

Symptoms in men may include urethral discharge, lower abdominal pain, scrotal swelling, and urinary problems. Most women with chlamydia experience vaginal or urethral discharge, pain and bleeding after intercourse, bladder problems.

Gonococcus (Neisseria Gonorrhoeae)

Gonorrhea is a bacterial infection that is usually spread through sexual contact. The incubation period of gonorrhea infection ranges from 1 day to 2-3 weeks. The infection is asymptomatic in approximately 20% of men and 50% of women.

The bacteria can infect not only the mucous membranes of the genitourinary organs but also the mouth, throat, and rectum. After gonococci penetrate the lining of the genitourinary organs, they rapidly multiply and cause an acute inflammatory response. This process is accompanied by abundant infiltration of white blood cells (leukocytes) into affected tissues and purulent discharge. A favorable clinical course of the disease after the elimination of gonococci results in the resolution of submucosal inflammatory infiltrate and restoration of damaged epithelium.

Treponema Pallidum 

Syphilis is a sexually transmitted infection that may become chronic. Syphilis causes the development of lesions that affect the skin, mucous membranes, internal organs, and also the musculoskeletal system.

Results of a Clinical Study on the Efficacy of Doxycycline

The study was led by Dr. Annie Lutkemeyer, a professor of infectious diseases at the University of California, San Francisco, and Dr. Connie Celum, a professor of global health, medicine, and epidemiology at the University of Washington.

The trial demonstrated a significant reduction in bacterial sexually transmitted infections among 554 participants who took doxycycline following unprotected sex, compared to the placebo group. The antibiotic was well tolerated by patients and did not cause side effects. Researches also found that the drug was especially effective for men who have sex with men and transgender women.

However, it remains unclear whether a single dose of doxycycline could lead to increased antibiotic resistance in bacteria that cause STIs. Besides, the trial is still studying the effects of the drug on the gut microbiota.

It’s no secret that having unprotected sex is risky, but it happens. Therefore scientists all over the world conduct various clinical trials on STDs. We have prepared a checklist to lower your chances of getting an infection after unprotected intercourse. But doctors do not recommend taking emergency measures, as well as antibiotics, instead of using condoms.

What to Do After Unprotected Sex

• The first step is to try to urinate immediately after sexual intercourse. The recommendation works for both men and women. The urine will flush out bacteria that may have entered the urethra, thus helping to prevent the development of inflammation. Bathing or showering is also essential.
• Within 3 hours after sex, you need to clean the genital area with an antiseptic solution. For example, you can use an aqueous chlorhexidine solution. Men should administer no more than 3-4 ml of antiseptic into the external opening of the urethra, and women can moisten a swab with antiseptic and insert it into the vagina for 15 minutes. Antiseptic and disinfectant agents negatively affect the mucous membrane of the urethra and vagina. For this reason, the method can be used no more than once a year.
• You need to get a pap smear (vaginal or urethral) not earlier than 3 weeks after unprotected sex to check for sexually transmitted diseases. You may wonder why we recommend a pap smear instead of a blood test. The answer is simple - infections latch onto the urethra and vagina.
• To test for syphilis, you will need to have a blood test not earlier than after 6 weeks. You should also test for HIV and hepatitis after 3 months.

It is critical to get tested for STDs even if you do not experience any symptoms. Some diseases may go unnoticed, turn into chronic cases and lead to complications over time. Since each disease has an incubation period, you should schedule the tests in order to avoid false-negative results. 

Remember to always use condoms. This will reduce the risk of infection and help keep your urinary system healthy.