Tetracyclines are medications of choice for infections with Chlamydia, Chlamydophila, Mycoplasma, Rickettsia, Ehrlichia, and Vibrio organisms and for some spirochetal infections. Sexually transmitted diseases in which chlamydiae often play a role—endocervicitis, urethritis, proctitis, and epididymitis—should be treated with doxycycline for 7–14 days. Pelvic inflammatory disease is often treated with doxycycline plus cefoxitin or cefotetan. Other chlamydial infections (psittacosis, lymphogranuloma venereum, trachoma) and sexually transmitted diseases (granuloma inguinale) also respond to doxycycline. Other uses include treatment of acne, respiratory infections, Lyme disease and relapsing fever, brucellosis, glanders, tularemia (often in combination with streptomycin), cholera, mycoplasmal pneumonia, actinomycosis, nocardiosis, malaria, infections caused by M marinum and Pasteurella species (typically after an animal bite), and as malaria prophylaxis (including multidrug-resistant P falciparum). They also have been used in combination with other medications for amebiasis, falciparum malaria, and recurrent ulcers due to H pylori. With its modest activity against pneumococci (same or better than macrolides) and reliable coverage of H influenzae, Chlamydophila, Legionella, and Mycoplasma organisms, doxycycline should be considered as a potential empiric therapy for mild to moderate outpatient pneumonia. Doxycycline and minocycline are options in the treatment of community-onset skin and soft tissue infection due to methicillin-resistant S aureus. As discussed previously, minocycline and doxycycline are superior to tetracycline in the treatment of methicillin-resistant S aureus; doxycycline-resistant isolates are often still inhibited by minocycline. Minocycline is equally as efficacious as doxycycline for the therapy of nongonococcal urethritis and cervicitis.
Hypersensitivity reactions with fever or skin rashes are uncommon.
B. Gastrointestinal Side Effects
Diarrhea, nausea, and anorexia are common. Tetracycline administration, particularly doxycycline and minocycline, should be avoided at bedtime due to the risk of esophageal erosion.
Tetracyclines are bound to calcium deposited in growing bones and teeth, causing fluorescence, discoloration, enamel dysplasia, deformity, or growth inhibition. Therefore, tetracyclines should not be given to pregnant women, nursing women, or children under 8 years of age. The warning regarding dental staining with tetracyclines and children has existed for decades. However, a study of children treated with doxycycline for suspected Rocky Mountain spotted fever revealed no dental staining, enamel hypoplasia, or tooth color differences in any patient. Consequently, certain children can likely receive doxycycline if other options are less favorable.
Tetracyclines can impair hepatic function or even cause liver necrosis, particularly in the presence of preexisting liver disease.
Demeclocycline, a tetracycline derivative, can cause nephrogenic diabetes insipidus and has been used therapeutically to treat inappropriate antidiuretic hormone secretion. Tetracyclines, particularly tetracycline, may increase blood urea nitrogen (BUN) due to their antianabolic activity.
All tetracyclines may induce photosensitization, especially in fair-skinned individuals. Minocycline induces vestibular reactions (dizziness, vertigo, nausea, vomiting), with a frequency of 35–70% associated with doses of 200 mg daily.