Doxycycline can be used for patients whose immune system is unable to fight off the infection caused by bacteria. Doxycycline is prescribed for the treatment of urinary tract infections, gonorrhea, chlamydia, acne and a number of others as determined by your health care provider. Make sure you take doxycycline at the same time every day. This is necessary to make sure you maintain the same level of the drug in your blood. Even if you feel better take the entire amount prescribed, as improved symptoms do not always mean the infection has been completely treated. If you stop the treatment too early a relapse of infection is possible.