Clarithromycin is a semi-synthetic macrolide antibiotic. Chemically it is 6-0 methylerythromycin. Like other macrolides, clarithromycin binds to the 50S subunit of the 70S ribosome, thereby blocking RNA-mediated bacterial protein synthesis. Clarithromycin can be bacteriostatic or bactericidal in action, depending on the concentration as well as the particular organism and its inoculum. The minimum inhibitory concentrations (MIC) of clarithromycin are generally two-fold lower than the MIC of erythromycin.


Clinical Pharmacology

Clarithromycin is rapidly and well absorbed from the gastro-intestinal tract after oral administration of clarithromycin. The microbiologically active metabolite 14-hydroxycalrithromycin is formed by first pass metabolism. Clarithromycin may be given without regard to meals as food does not affect the extent of bioavailability of clarithromycin. Food does slightly delay the onset of absorption of clarithromycin and formation of the 14-hydroxymelabolite. The pharmacokinetics of clarithromycin are non-linear; however, steady state is attained with 2days of dosing. At 250 mg bid daily 15-20% of unchanged drug is excreted in the urine. With 500mg b.i.d daily dosing urinary excretion is greater (app.36%).

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Clarithromycin provides tissue concentrations that are several times higher than the circulating drug levels. Increased levels have been found in both tonsillar and lung tissue. Clarithromycin is 80% bound to plasma proteins at therapeutic levels. Clarithromycin also penetrates the gastric mucus. Level of clarithromycin in gastric acid mucus and gastric tissues are higher when clarithromycin is co-administered with omeprazole than when clarithromycin is administered alone. Clarithromycin penetrates into the middle ear fluid at concentrations greater than in the serum.