A tetracycline is the drug of choice in the treatment of most infections caused by rickettsiae and Borrelia sp, including Rocky Mountain spotted fever and Lyme disease. Tetracyclines are used preferentially to treat Anaplasma phagocytophilum and Ehrlichia sp. Tetracyclines are also excellent drugs for the treatment of Mycoplasma pneumoniae, chlamydiae, and some spirochetes. They are used in combination regimens to treat gastric and duodenal ulcer disease caused by Helicobacter pylori. They may be used in various Gram-positive and Gram-negative bacterial infections, including vibrio infections, provided the organism is not resistant. In cholera, tetracyclines rapidly stop the shedding of vibrios, but tetracycline resistance is an increasing problem. Tetracyclines remain effective in most chlamydial infections, including sexually transmitted infections. Doxycycline is also an alternative agent recommended by the Centers for Disease Control and Prevention for primary and secondary syphilis in patients with penicillin allergy. A tetracycline—in combination with other antibiotics—is indicated for plague, tularemia, and brucellosis. Tetracyclines are sometimes used in the treatment or prophylaxis of protozoal infections, eg, those due to Plasmodium falciparum (see Chapter 52). Other uses include treatment of acne, exacerbations of bronchitis, community-acquired pneumonia, leptospirosis, and some nontuberculous mycobacterial infections (eg, Mycobacterium marinum). Tetracyclines formerly were used for a variety of common infections, including bacterial gastroenteritis and urinary tract infections. However, many strains of bacteria causing these infections are now resistant, and other agents have largely supplanted tetracyclines.
Minocycline, 100 mg orally twice daily for 5 days, can eradicate the meningococcal carrier state, but because of side effects and resistance of many meningococcal strains, ciprofloxacin or rifampin is preferred. Demeclocycline is rarely used as an antibacterial, but it has been used off-label in the treatment of inappropriate secretion of antidiuretic hormone because of its inhibition of antidiuretic hormone in the renal tubule (see Chapter 15).
Tigecycline, the first glycylcycline to reach clinical practice, has several unique features that warrant its consideration apart from the older tetracyclines. Its spectrum is very broad, and many tetracycline-resistant strains are susceptible to tigecycline because it is not affected by the common resistance determinants. Susceptible organisms include coagulase-negative staphylococci and Staphylococcus aureus, including methicillin-resistant, vancomycin-intermediate, and vancomycin-resistant strains; streptococci, penicillin-susceptible and resistant; enterococci, including vancomycin-resistant strains; Gram-positive rods; Enterobacteriaceae; multidrug-resistant strains of Acinetobacter sp; anaerobes, both Gram-positive and Gram-negative; rickettsiae, Chlamydia sp, and Legionella pneumophila; and rapidly growing mycobacteria. Proteus and Providencia sp and P aeruginosa, however, are intrinsically resistant.