1. Clinical Overview
Clarithromycin is a semi-synthetic macrolide antibiotic derived from erythromycin. It is a broad-spectrum antibiotic with enhanced acid stability and improved oral bioavailability compared to erythromycin. It is widely used in the Indian context for treating respiratory tract infections, skin and soft tissue infections, and Helicobacter pylori eradication. It acts by inhibiting bacterial protein synthesis.
| Onset | Duration | Bioavailability |
|---|---|---|
| Peak plasma concentrations are achieved in approximately 2-3 hours after oral administration. | Approximately 12 hours, supporting a twice-daily (BID) dosing regimen. | Approximately 50-55% for the immediate-release tablet. |
2. Mechanism of Action
Clarithromycin binds reversibly to the 50S subunit of the bacterial ribosome, specifically at the peptidyl transferase center. This binding inhibits the translocation step of protein synthesis, preventing the transfer of the peptidyl-tRNA from the A-site to the P-site. This results in the arrest of bacterial protein chain elongation, leading to bacteriostatic activity against susceptible organisms.
3. Indications & Uses
- Acute bacterial exacerbation of chronic bronchitis
- Community-acquired pneumonia (mild to moderate)
- Acute maxillary sinusitis
- Pharyngitis/Tonsillitis (caused by S. pyogenes)
- Uncomplicated skin and skin structure infections
4. Dosage & Administration
Adult Dosage: For most infections: 250-500 mg orally every 12 hours for 7-14 days. For H. pylori eradication: 500 mg twice daily as part of combination therapy for 10-14 days.
Administration: Tablet can be taken with or without food. Should be swallowed whole with a full glass of water. Do not crush, chew, or break the extended-release tablets. For optimal absorption and to minimize GI upset, taking with food is often recommended.
5. Side Effects
Common side effects may include:
- Nausea
- Diarrhea
- Abdominal pain/discomfort
- Dyspepsia
- Headache
- Altered taste (metallic taste)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin | Increased anticoagulant effect, risk of bleeding | Major |
| Statins (Atorvastatin, Simvastatin, Lovastatin) | Increased risk of myopathy/rhabdomyolysis | Major |
| Colchicine | Increased colchicine toxicity (myelosuppression, multiorgan failure) | Contraindicated in renal/hepatic impairment |
| Midazolam, Triazolam | Increased and prolonged sedation | Major |
| Digoxin | Increased digoxin serum levels (P-gp inhibition) | Moderate |
| Theophylline | Increased theophylline serum levels | Moderate |
| Carbamazepine | Increased carbamazepine toxicity | Major |
| Protease Inhibitors (Ritonavir, Saquinavir) | Mutual inhibition of metabolism; increased risk of QT prolongation | Major |
| Cyclosporine, Tacrolimus | Increased immunosuppressant levels, risk of nephrotoxicity | Major |
| Oral Hypoglycemics (e.g., Glimepiride) | Enhanced hypoglycemic effect | Moderate |
| Sildenafil, Tadalafil | Increased PDE5 inhibitor levels and adverse effects | Moderate |
| Efavirenz, Nevirapine | Decreased clarithromycin levels; increased metabolite levels | Moderate |
7. Patient Counselling
- DO complete the full course of therapy even if you feel better.
- DO take the medicine at evenly spaced intervals (every 12 hours).
- DO inform your doctor about all other medicines, vitamins, and supplements you are taking.
- DO report any severe diarrhea, even if it occurs weeks after finishing the antibiotic.
- DONT skip doses.
- DONT share your medicine with others.
- DONT take antacids containing aluminum or magnesium within 2 hours of taking clarithromycin, as they may reduce absorption.
8. Toxicology & Storage
Overdose: Symptoms are an extension of side effects: severe nausea, vomiting, diarrhea, epigastric distress, reversible hearing loss. In massive overdose, potential for QT prolongation leading to arrhythmias.
Storage: Store at room temperature (15-30°C), in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.