Doxycycline is a widely prescribed tetracycline antibiotic effective against various bacterial infections, including those affecting the respiratory tract, skin, and urinary system. Its broad-spectrum activity also makes it a valuable tool in treating certain sexually transmitted infections (STIs).
Effectiveness Against Specific STIs
Doxycycline is a primary treatment option for chlamydia, a common bacterial STI. For uncomplicated chlamydial infections of the urethra, cervix, or rectum, the recommended dosage is 100 milligrams (mg) taken orally twice daily for seven days. This regimen is effective in eradicating the infection.
While not a first-line monotherapy for gonorrhea due to increasing resistance, doxycycline plays a role in its management, particularly when chlamydia co-infection is present. When treating gonorrhea, healthcare providers often prescribe a single injection of ceftriaxone, along with doxycycline 100 mg orally twice daily for seven days, if chlamydial infection has not been ruled out. Doxycycline is also recognized for its use in post-exposure prophylaxis (PEP) against gonorrhea, chlamydia, and syphilis in certain high-risk populations.
For individuals allergic to penicillin, doxycycline serves as an alternative treatment for syphilis. For early syphilis, which includes primary, secondary, or early latent stages, the typical dosage is 100 mg orally twice daily for 14 days. In cases of late latent syphilis, the treatment duration extends to 28 days at the same dosage.
Doxycycline is also used in the management of Mycoplasma genitalium infections, often as an initial step in a two-stage treatment approach. A common regimen involves 100 mg orally twice daily for seven days, which helps reduce the bacterial load. This initial course is typically followed by another antibiotic, such as azithromycin or moxifloxacin, especially in cases of macrolide resistance, as doxycycline alone has a lower cure rate for Mycoplasma genitalium.
Lymphogranuloma Venereum (LGV), a specific type of chlamydial infection, also responds to doxycycline. The recommended treatment for LGV is 100 mg orally twice daily for 21 days.
How Doxycycline Works
Doxycycline functions as a bacteriostatic antibiotic, meaning it acts by inhibiting the growth and reproduction of bacteria rather than directly killing them. It achieves this by targeting the bacteria’s protein synthesis machinery. Specifically, doxycycline binds to the 30S ribosomal subunit within bacterial cells. This binding action prevents the bacteria from assembling essential proteins necessary for their survival, growth, and replication. This inhibition then allows the body’s own immune system to clear the remaining infection.
Important Treatment Considerations
Adhering to the prescribed course of doxycycline is important for successful treatment. Patients should complete the full duration of medication, even if their symptoms improve before the course is finished. Stopping treatment early can lead to treatment failure and may contribute to the development of antibiotic resistance.
Doxycycline can cause certain side effects, with photosensitivity being a notable concern, increasing the risk of sunburn. Gastrointestinal upset, including nausea, vomiting, and abdominal pain, is also common. Taking the medication with food or milk and remaining upright for at least one hour after ingestion can help mitigate these digestive issues and reduce the risk of esophageal irritation.
Patients should also inform their healthcare provider about all other medications and supplements they are taking. Doxycycline can interact with certain substances, such as antacids, iron supplements, and potentially oral contraceptives.
During treatment for an STI, it is important to abstain from sexual activity. This abstinence should continue until the full course of medication is completed and any symptoms have resolved. Additionally, sexual activity should be avoided until all sexual partners have been tested and, if necessary, treated, to prevent re-infection and further transmission.
Follow-up testing may be recommended after completing treatment for certain STIs, such as gonorrhea or Mycoplasma genitalium. This “test of cure” ensures the infection has been successfully eradicated. It is also crucial for individuals to inform their sexual partners about their STI diagnosis so that partners can also be tested and treated. While doxycycline effectively treats existing bacterial STIs, it does not offer protection against future infections; therefore, consistent safe sex practices remain important for prevention.