Like other macrolide antibiotics, clarythromycin penetrates the cell wall of bacteria and reversibly binds to domain V of the 23S ribosomal RNA of the 50S subunit of the bacterial ribosome. This blocks the translocation of aminoacyl transfer RNA and polypeptide synthesis. As a result, the bacterial cells can no longer produce proteins and are therefore unable to reproduce. After ingestion, claryhtromycin is partially converted into the metabolite 14-OH-clarithromycin, which is also active and acts synergistically with the parent compound.
Clarithromycin also inhibits the hepatic microsomal CYP3A4 isoenzyme and P-glycoprotein, an energy-dependent drug efflux pump.
Clarithromycin is well absorbed after oral administration, is acid stable, and can be taken with food. Bioavailability is approximately 50%. It is approximately 70% bound to plasma proteins in the blood. It is metabolized predominantly by the enzyme CYP3A4 in the liver. This may result in a number of drug-drug interactions. The elimination half-life is approximately 3-4 hours.
Clarithromycin inhibits the liver enzyme, CYP3A4, which is involved in the metabolism of many other commonly prescribed drugs. Taking clarithromycin together with other drugs metabolized by CYP3A4 may result in unexpected increases or decreases in plasma levels of these agents.
Drugs with a high risk for interactions include:
- Colchicine (risk of fatal colchicine toxicity result, especially in people with chronic kidney disease).
- Statins (risk of severe muscle pain and rhabdomyolysis).
- Verapamil (risk for hypotension, bradycardia, and lactic acidosis)
- Carbamazepine (risk for seeing double vision, dizziness, ataxia, and hyponatremia)
- HIV medications (plasma levels and effect may be reduced)