Tetracyclines, chloramphenicol, erythromycin, and clindamycin.

Tetracyclines are active in vitro against most urinary tract pathogens, 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, Streptococcus pneumoniae, and group A beta-hemolytic streptococci. Erythromycin may 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 only for the treatment of anaerobic infections. Tetracycline may cause gastrointestinal upset; phototoxic dermatitis; hepatitis, especially in pregnant females; discoloration of teeth and bone dysplasia in the human fetus and children; and suprainfections, especially oral and anogenital candidiasis. Tetracycline 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 and idiosyncratic. The incidence of undesirable side effects associated with the use of erythromycin is low. Gastrointestinal irritation is the most common; cholestatic hepatitis may occur with erythromycin estolate. Pseudomembranous colitis is the most important toxic effect associated with clindamycin.