Tetracyclines, chloramphenicol, erythromycin, and clindamycin.

The tetracyclines are active in vitro against many urinary tract pathogens such as Chlamydia, Mycoplasma pneumoniae, Brucella, rickettsiae, and Nocardia. Chloramphenicol is used primarily for anaerobic infections, Haemophilus influenzae meningitis, and infections due to Salmonella typhi. Erythromycin is active in vitro against M. pneumoniae, Legionella spp., Streptococcus pneumoniae, and group A beta-hemolytic streptococci; it may also be used as prophylactic therapy for subacute bacterial endocarditis and for recurrence of acute rheumatic fever in patients who are allergic to penicillin. Clindamycin should be used primarily for the treatment of anaerobic infections. The tetracyclines may cause gastrointestinal upset; phototoxic dermatitis; hepatitis, especially in pregnant women; discoloration of the teeth and bone dysplasia in the human fetus and in children; and superinfections, especially oral and anogenital candidiasis. The tetracyclines should be used with caution in patients with renal insufficiency. The most important toxic effect of chloramphenicol is bone marrow suppression, which is dose related or idiosyncratic. The incidence of undesirable side effects associated with the use of erythromycin is low; gastrointestinal irritation is the most common, and cholestatic hepatitis may occur with the use of erythromycin estolate. Pseudomembranous colitis is the most important toxic effect associated with the use of clindamycin.