Klacid (Clarithromycin)

Clarithromycin is a macrolide antibiotic used to treat infections caused by susceptible bacteria.

• Community‑acquired pneumonia: eradicates the causative organisms and improves respiratory function.
• Acute bacterial sinusitis: reduces sinus inflammation and clears infection.
• Acute exacerbations of chronic bronchitis: helps restore airway patency and reduces bacterial load.
• Skin and soft‑tissue infections: eliminates pathogenic bacteria in dermal lesions.
• Helicobacter pylori eradication: part of combination therapy to achieve bacterial clearance.

• Clarithromycin binds to the 50S subunit of bacterial ribosomes, inhibiting translocation of the peptidyl‑tRNA. This blocks protein synthesis, leading to a bacteriostatic effect against susceptible Gram‑positive, Gram‑negative and atypical organisms.

Clarithromycin may cause a range of adverse reactions, from mild to severe.

Common Side Effects

• Nausea: mild to moderate upset stomach.
• Diarrhea: loose stools, sometimes watery.
• Abdominal pain: cramping or discomfort.
• Altered taste: metallic or bitter sensation.
• Headache: mild to moderate intensity.
• Vomiting: occasional episodes.

Serious or Rare Side Effects

• Anaphylaxis: severe allergic reaction requiring immediate care.
• QT interval prolongation: risk of cardiac arrhythmias.
• Clostridioides difficile‑associated diarrhea: severe colitis.
• Hepatic enzyme elevation: potential liver injury.
• Stevens‑Johnson syndrome/toxic epidermal necrolysis: severe skin reactions.
• Cardiac arrhythmias: irregular heartbeat beyond QT issues.

Before prescribing clarithromycin, clinicians should evaluate patient‑specific risk factors.

• Renal or hepatic impairment: adjust therapy based on function.
• QT prolongation risk: avoid in patients with known cardiac conduction disorders.
• Known hypersensitivity: do not use in individuals allergic to macrolides.
• Concomitant CYP3A4 substrates: monitor for increased exposure.
• Pregnancy and lactation: assess benefit‑risk, as safety data are limited.
• Store at room temperature: keep in original container, protect from moisture and light.

Clarithromycin interacts with several medicines; awareness of interaction severity guides clinical decisions.

Major Interactions (Avoid)

• Cisapride, pimozide: risk of fatal arrhythmias.
• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): may cause toxic clarithromycin levels.
• Colchicine in renal failure: heightened risk of toxicity.
• Simvastatin or lovastatin: increased risk of rhabdomyolysis.
• Ergot alkaloids: precipitate severe vasospasm.

Moderate Interactions (Monitor Closely)

• Warfarin: possible INR elevation.
• Carbamazepine, phenytoin: reduced clarithromycin efficacy.
• Digoxin: increased serum concentrations.
• Oral contraceptives: decreased hormonal effectiveness.
• Theophylline: heightened plasma levels.