Klacid (Clarithromycin)

Clarithromycin (Klacid) is indicated for bacterial infections affecting the respiratory, sinus, skin and gastrointestinal systems.

• Community‑acquired pneumonia: effective in treating infection caused by susceptible Streptococcus pneumoniae and other pathogens.
• Acute bacterial sinusitis: reduces symptoms and bacterial load in patients with sinus infection.
• Skin and soft‑tissue infections: resolves infections such as cellulitis and erysipelas caused by susceptible organisms.
• Helicobacter pylori eradication (in combination therapy): contributes to eradication regimens when used with other antibiotics and a proton‑pump inhibitor.

• Clarithromycin binds to the 50S subunit of bacterial ribosomes, blocking the translocation step of protein synthesis. This inhibition prevents peptide chain elongation, leading to a bacteriostatic effect against susceptible Gram‑positive and some Gram‑negative organisms. By interfering with ribosomal function, the drug halts bacterial growth without directly damaging host cells. The binding site is distinct from that of other macrolides, providing a broad spectrum of activity and reducing cross‑resistance.

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

Common Side Effects

• Nausea: mild stomach upset often occurring after dosing.
• Diarrhea: loose stools that may be self‑limiting.
• Taste disturbance: a temporary metallic or bitter taste.
• Abdominal pain: cramping or discomfort in the stomach area.

Serious or Rare Side Effects

• Severe allergic reaction: rash, itching, swelling, or anaphylaxis requiring immediate medical attention.
• Liver enzyme elevation: significant increase in hepatic transaminases indicating possible hepatotoxicity.
• Cardiac arrhythmia: QT interval prolongation leading to irregular heart rhythm, especially in patients with pre‑existing cardiac conditions.

Before prescribing clarithromycin, clinicians should consider several precautionary measures to ensure safe use.

• Assess renal and hepatic function: dose adjustment may be needed in patients with impairment.
• Review concomitant medications: avoid drugs that prolong QT interval or are metabolized by CYP3A4.
• Monitor for allergic reactions: discontinue if rash, swelling, or breathing difficulty develop.
• Use caution in pregnancy: limited data, risk‑benefit assessment required.
• Avoid in patients with known macrolide hypersensitivity: contraindicated.
• Store at ambient temperature: keep in original container, protect from moisture and heat.

Clarithromycin interacts with several medicines through enzyme inhibition and additive pharmacodynamic effects.

Major Interactions (Avoid)

• CYP3A4 substrates with narrow therapeutic index (e.g., simvastatin, tacrolimus): risk of toxicity; co‑administration should be avoided.
• QT‑prolonging agents (e.g., quinidine, sotalol): may cause serious arrhythmias; avoid combined use.
• Ergot alkaloids (e.g., ergotamine): risk of ergotism; contraindicated.

Moderate Interactions (Monitor Closely)

• Warfarin: increased anticoagulant effect; monitor INR.
• Theophylline: elevated levels may cause toxicity; monitor clinical response.
• Oral contraceptives: reduced efficacy; advise alternative contraception.