It is a particularly useful, inexpensive agent for treatment of asymptomatic cystitis in women and a wide range of other conditions in both women and men, including Lyme disease, nongonococcal urethritis, cholera, brucellosis, several rickettsial infections, sinusitis, otitis, acute exacerbation of chronic bronchitis, and community-acquired pneumonia. American Thoracic Society guidelines for community-acquired pneumonia recommend doxycycline as an alternative to macrolides. Considering the expense of the macrolides, and the fact that erythromycin is poorly tolerated, doxycycline is the drug I most frequently use in outpatient treatment of pneumonia. Doxycycline is well absorbed orally, but about half of the dose is converted to inactive compounds. Photosensitive skin reactions ranging in severity from paraesthesia in sun-exposed areas to frank erythema have been attributed to doxycycline use.
More severe reactions are uncommon.
Antacids and iron supplements may delay absorption, but food has no effect. An increased prothrombin time may occur if doxycycline is administered in the presence of warfarin. It is ineffective against methicillin-resistant staphylococci and enterococci. Its primary use, therefore, is in the treatment of abdominal and pelvic infections, aspiration pneumonia, and diabetic foot infections, in which anaerobic organisms may play a role. In several such conditions, an additional agent may be necessary to combat coexisting gram-negative pathogens.