Protein Synthesis Inhibitors : 1

Erythromycin

MOA: Drug binds exclusively to the 50S subunit where it blocks the translocation step in which the peptidyl tRNA is shifted from the acceptor (A) site back to the peptide (P) site. Bacteriostatic.

Spectrum: Used primarily against G(+) infections in patients sensitive to penicillin. Also effective against G(-) N. gonorrhea, N. meningitidis, H. influenzae, B. pertussis.

Resistance: 1. Genetically altered ribosomal protein; 2. Decreased permeability to drug; 3. Induced resistance (unique to erythromycin, due to low dose). Resistance to one macrolide induces resistance to all.

Pharmacokinetics: Administered as an ester to reduce acid lability. Metabolized by liver, with high concentrations found in bile and feces. Erythromycin inhibits cytochrome p450.

Therapeutic place: Used when the patient is sensitive to penicillin. Used to treat Legionnaire’s disease, M. pneumoniae, pertussis, and as an alternate drug for Lyme’s disease and chlamydia.

Clarithromycin – Used to treat M. avium-intracellulare infections in AIDS patients as well as peptic ulcers caused by H. pylori.

Azithromycin – Used to treat M. avium-intracellulare and toxoplasmosis encephalitis in AIDS patients.

Category: Pharmacology Notes