Erythromycin

Erythromycin is poorly soluble in water but dissolves readily in organic solvents. They Erythromycins are usually dispensed as various esters and salts.

Antimicrobial Activity: Erythromycin is effective against gram-positive organisms, especially pneumococci, streptococci, staphylococci, and corynebacteria. Mycoplasma, Legionella, Chlamydia trachomatis, Helicobacter, Listeria, Mycobacterium kansasii, and Mycobacterium scrofulaceum are also susceptible. Gram-negative organisms such as Neisseria species, Bordetella pertussis, Treponema pallidum, and Campylobacter species are susceptible.

Pharmacokinetics: Erythromycin base is destroyed by stomach acid and must be administered with enteric coating. Food interferes with absorption. Stearates and esters are fairly acid- resistant and somewhat better absorbed. Large amounts of an administered dose are excreted in the bile and lost in feces. Absorbed drug is distributed widely except to the brain and cerebrospinal fluid.

Clinical Uses: Erythromycin is the drug of choice in corynebacterial infections (diphtheria, corynebacterial sepsis, erythrasma); in respiratory, neonatal, ocular, or genital chlamydial infections; and in treatment of community-acquired pneumonia because its spectrum of activity includes the pneumococcus, Mycoplasma, and Legionella. Erythromycin is also useful as a penicillin substitute in penicillin-allergic individuals with infections caused by staphylococci, streptococci, or pneumococci.

Adverse Reactions

Gastrointestinal Effects: Anorexia, nausea, vomiting, and diarrhea.

Liver Toxicity: Erythromycins, particularly the estolate, can produce acute cholestatic hepatitis (reversibile).

Drug Interactions: Erythromycin metabolites inhibit cytochrome P450 enzymes; hence increase the serum concentrations of theophylline, oral anticoagulants, and terfenadine. It increases serum concentrations of oral digoxin by increasing its bioavailability.