Klaryz Mechanism of Action

Pharmacology: Clarithromycin is rapidly absorbed from the gastrointestinal tract following oral administration and undergoes first-pass metabolism; the bioavailability of the parent drug is about 55%. The extent of absorption is relatively unaffected by the presence of food. Peak concentrations of clarithromycin and its principal active metabolite 14-hydroxyclarithromycin are reported to be about 0.6 and 0.7 g per mL respectively following a single 250 mg dose by mouth; at steady state the same dosage given every 12 hours as tablets produces peak concentrations of clarithromycin of about 1 g per mL. The same dose given as a suspension produces a steady state plasma concentration of about 2 g per mL.
The pharmacokinetics of clarithromycin is nonlinear and dose dependent; high doses may produce disproportionate increase in peak concentration of the parent drug, due to saturation of the metabolic pathways.
The drug and its principal metabolite are widely distributed and tissue concentrations exceed those in serum, in part because of intracellular uptake. Clarithromycin has been detected in breast milk. It is extensively metabolized in the liver and excreted in feces via the bile. Substantial amount are excreted in urine; at a steady state about 20% and 30%, respectively of a 250 mg or 500 mg dose is excreted in this way, as unchanged drug. 14-hydroxyclarithromycin as well as other metabolites are also excreted in the urine accounting for 10 to 15% of the dose. The terminal half-life of Clarithromycin is reportedly about 3 to 4 hours in patients receiving 250 mg doses twice daily and about 5 to 7 hours in those receiving 500 mg twice daily. The half-life is prolonged in renal impairment.