clarithromycin

Clarithromycin is a macrolide antibiotic used to treat a range of bacterial infections. It is a semi-synthetic derivative of erythromycin with improved acid stability and oral bioavailability. Clarithromycin works by binding reversibly to the 50S ribosomal subunit of susceptible bacteria, inhibiting translocation and protein synthesis.

The drug has activity against many Gram-positive cocci, including Streptococcus pneumoniae and Staphylococcus aureus (some strains), as well as Haemophilus influenzae and Moraxella catarrhalis. It also covers atypical pathogens such as Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella species. Clinically, clarithromycin is used for acute otitis media, sinusitis, pharyngitis/tonsillitis, community-acquired pneumonia, and some skin and soft tissue infections. It is also used in combination regimens for Helicobacter pylori eradication in peptic ulcer disease, typically alongside antibiotics and a proton pump inhibitor.

Pharmacokinetics: clarithromycin is well absorbed orally and can be given intravenously. It is metabolized in the liver to 14-hydroxyclarithromycin, an active metabolite, and is primarily eliminated via biliary excretion with a smaller renal component. The elimination half-life is roughly 3 to 4 hours for the parent drug.

Adverse effects and interactions: common adverse effects include gastrointestinal upset, altered taste, and headache. Hepatotoxicity is rare but possible. Clarithromycin inhibits cytochrome P450 3A4 and can raise the levels of drugs such as statins, certain anticoagulants, and some antiarrhythmics; caution is advised with QT-prolonging agents and in patients with liver disease or electrolyte disturbances. Pregnancy category C; breastfeeding should be avoided if possible.

Dosing: adults are commonly prescribed 250 mg every 12 hours for many infections, or 500 mg every 12 hours for certain illnesses; treatment duration varies. For Helicobacter pylori therapy, 500 mg twice daily is used in combination with other agents for 7–14 days.