Klacid Sr (Clarithromycin)

Clarithromycin is a macrolide antibiotic indicated for several bacterial infections affecting the respiratory tract, skin and gastrointestinal system.

• Community-acquired pneumonia: effective treatment of susceptible bacterial pathogens causing lung infection.
• Acute bacterial sinusitis: resolves sinus inflammation caused by susceptible bacteria.
• Acute bacterial exacerbations of chronic bronchitis: reduces bacterial load and improves symptoms.
• Skin and soft tissue infections: treats infections such as cellulitis and erysipelas caused by susceptible organisms.
• Helicobacter pylori eradication: used in combination regimens to eliminate H. pylori infection.

• Clarithromycin binds to the 50S subunit of bacterial ribosomes, inhibiting the translocation step of protein synthesis. This blockade prevents elongation of the nascent peptide chain, halting bacterial growth. By targeting a conserved ribosomal site, the drug exhibits bacteriostatic activity against a broad spectrum of Gram‑positive and some Gram‑negative organisms, and it may be bactericidal at higher concentrations. It also interferes with bacterial adherence and reduces toxin production.

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

Common Side Effects

• Nausea: mild to moderate stomach upset that may occur shortly after taking the medication.
• Diarrhea: loose, watery stools that can be intermittent during therapy.
• Taste disturbance: a temporary altered or metallic taste in the mouth.
• Headache: mild to moderate headache that usually resolves without intervention.

Serious or Rare Side Effects

• Clostridioides difficile-associated diarrhea: severe colitis presenting with profuse watery stools and abdominal pain, requiring prompt medical care.
• QT interval prolongation: elongation of the cardiac repolarization phase that can predispose to serious arrhythmias.
• Stevens‑Johnson syndrome/toxic epidermal necrolysis: rare, life‑threatening skin and mucous membrane reactions characterized by blistering and detachment.

When prescribing clarithromycin, clinicians should consider several safety measures to minimize risks.

• Assess renal function: adjust therapy in patients with significant renal impairment.
• Monitor liver enzymes: watch for signs of hepatotoxicity during treatment.
• Avoid use in patients with known macrolide allergy: risk of hypersensitivity reactions.
• Use caution in patients with QT prolongation risk: evaluate cardiac history and concomitant drugs.
• Discuss pregnancy and breastfeeding: clarithromycin is Category B; benefits should outweigh potential risks.
• Store at room temperature: keep tablets in the original container, protect from moisture and heat.

Clarithromycin interacts with several medicines; some combinations must be avoided while others require careful monitoring.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): may cause toxic clarithromycin levels.
• Concomitant QT‑prolonging agents (e.g., quinidine, sotalol): increase risk of serious cardiac arrhythmias.

Moderate Interactions (Monitor Closely)

• Statins (especially simvastatin, lovastatin): increased risk of myopathy and rhabdomyolysis.
• Warfarin: clarithromycin may enhance anticoagulant effect, requiring INR monitoring.
• Theophylline: plasma concentrations may rise, leading to toxicity.
• Carbamazepine: may reduce clarithromycin concentrations, decreasing efficacy.