Macrolides

ACTION

The macrolides are effective against a wide variety of pathogenic organisms, particularly infections of the respiratory and genital tract The macrolides are bacteriostatic or bactericidal in susceptible bacteria. The drugs act by binding to cell membranes and causingchanges in protein function.

USES

These antibiotics are effective in the treatment of infections caused by a wide range of gram-negative and gram positive microorganisms. In addition, the drugs are usedto treat acne vulgaris and skin infections, in conjunction with sulfonamides to treat upper respiratory infections caused by Hemophilus influenzae, and as prophylaxis before dental or other procedures in patients allergic to penicillin.

ADVERSE REACTIONS

Most of the adverse reactions seen with the administration of azithromycin and clarithromycin are related to the gastrointestinal tract and include nausea, vomiting, diarrhea, and abdominal pain. Abdominal cramping, nausea, vomiting, diarrhea, and allergic reactions have been reported with the administration of erythromycin. However, there appears to be a low incidence of adverse reactions associated with normal oral doses of erythromycin. As with almost all antibacterial drugs, pseudomembranous colitis may occur ranging in severity from mild to life threatening.

CONTRAINDICATIONS

These drugs are contraindicated in patients with a hypersensitivity to the macrolides and patients with pre-existing liver disease.

PRECAUTIONS

It is important to use these drugs cautiously during pregnancy and lactation. Azithromycin and erythromycin are Pregnancy Category B drugs, and clarithromycin, dirithromycin, and troleandomycin are Pregnancy Category C drugs. Because azithromycin, erythromycin, and troleandomycin are primarily eliminated from the body by the liver, these drugs should be used with great caution in patients with liver dysfunction. There is a decreased gastrointestinal absorption of the macrolides when administered with kaolin, aluminum salts, or magaldrate.

INTERACTIONS

Use of the macrolides increases serum levels of digoxin and increases the effects of anticoagulants. Use of antacids decreases the absorption of most macrolides. The macrolides should not be administered with clindamycin, lincomycin, or chloramphenicol; a decrease in the therapeutic activity of the macrolides can occur.

Concurrent administration of the macrolides with theophylline may increase serum theophylline levels. The macrolides can be use to treat community acquired pneumonia, pertussis (whooping cough), or for uncomplicated skin infections, among other susceptible infections. Ketolides are a newer generation of antibiotic developed to overcome macrolide bacterial resistance. Frequently prescribed macrolides are:

azithromycin (Zithromax)
clarithromycin (Biaxin)
erythromycin