Clarithromycin

BRAND NAMES

• The most widely recognized brand names for clarithromycin are Biaxin and Biaxin XL. Other brands include Klaricid, Claribid, and Klacid.

• Biaxin / Biaxin XL: The primary brand in the United States, available in both standard and extended-release tablets.

• Klaricid / Klaricid XL: Commonly used in the UK and other regions, also offered in regular and extended-release formulations.

• Claribid: Another brand for clarithromycin tablets.

• Klacid: Used in select countries for clarithromycin therapy.

MECHANISM OF ACTION

Clarithromycin is a macrolide antibiotic that works by blocking bacterial protein synthesis. It binds to the 50S ribosomal subunit, preventing translocation of peptides during translation. This action is primarily bacteriostatic but can be bactericidal at higher concentrations. It is effective against Gram-positive bacteria, some Gram-negative bacteria, and atypical pathogens such as Mycoplasma and Chlamydia. Clarithromycin also has anti-inflammatory properties, which may help in certain infections.

PHARMACOKINETICS:

Absorption: Clarithromycin is well absorbed orally, with peak plasma concentrations reached within 2–3 hours. Food may slightly delay absorption but does not reduce overall bioavailability.

Distribution: Widely distributed in body tissues, including respiratory tract, tonsils, skin, and sinuses. It penetrates intracellular compartments, which helps target intracellular pathogens.

Metabolism: Partially metabolized in the liver to an active metabolite, 14-hydroxyclarithromycin, which also contributes to antibacterial activity.

Excretion: Excreted mainly through the kidneys via urine, with a smaller fraction eliminated in feces. Dose adjustments may be required in renal impairment.

PHARMACODYNAMICS

Clarithromycin’s bacteriostatic action inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. Its active metabolite extends the antibacterial effect. It is effective against susceptible strains of Streptococcus, Staphylococcus, Haemophilus influenzae, Mycobacterium avium, and Helicobacter pylori. Clarithromycin also exhibits anti-inflammatory activity, which helps reduce tissue damage during infection.

ADMINISTRATION

Clarithromycin is administered orally in tablet or suspension form. Extended-release formulations are taken less frequently, typically once daily. Standard tablets are usually taken twice daily. It may be taken either with or without food; however, taking it with meals can help minimize stomach discomfort.

DOSAGE AND STRENGTH

• Immediate-release tablets: 250 mg or 500 mg, typically every 12 hours.

• Extended-release tablets: 500 mg or 1000 mg once daily.

• Oral suspension: 125 mg/5 mL or 250 mg/5 mL, dosed based on age and weight for children.

• Duration of therapy depends on infection type, usually 7–14 days.

• Dose adjustments may be required in renal impairment.

DRUG INTERACTIONS

Clarithromycin inhibits CYP3A4, which can increase levels of:

• Statins (e.g., simvastatin, atorvastatin)

• Warfarin

• Benzodiazepines (e.g., midazolam, triazolam)

• Certain antiarrhythmics (e.g., amiodarone)

Co-administration requires careful monitoring to prevent toxicity or adverse effects.

FOOD INTERACTIONS

Food does not significantly affect clarithromycin’s absorption, though taking it with meals may reduce gastrointestinal discomfort. Grapefruit juice may increase blood levels slightly and should be consumed cautiously. Maintaining consistent administration with regard to meals helps ensure stable drug levels.

CONTRAINDICATIONS

Clarithromycin is contraindicated in individuals with known hypersensitivity to clarithromycin, other macrolide, or ketolide antibiotics. It should be used with caution or avoided in patients with severe hepatic or renal impairment unless appropriate dose adjustments are made. The drug must not be taken with medications that rely heavily on CYP3A4 metabolism when there is a significant risk of interaction. Patients with a history of QT prolongation or ventricular arrhythmias should avoid its use. Additionally, clarithromycin should be used during pregnancy or breastfeeding only under medical supervision.

SIDE EFFECTS

• Nausea, vomiting, diarrhea, and abdominal pain.

• Taste disturbances (metallic or bitter taste).

• Headache and dizziness.

• Rash or mild allergic reactions.

• Rare: liver enzyme elevation, QT prolongation, or severe allergic reactions.

OVER DOSE

Symptoms of overdose may include severe nausea, vomiting, abdominal pain, and potentially liver or kidney toxicity. Management is largely supportive, including monitoring vital signs, hydration, and liver and kidney function. Activated charcoal may be used if ingestion is recent.

TOXICITY

Clarithromycin toxicity is uncommon but can occur with high doses or prolonged therapy. Potential effects include liver dysfunction, QT prolongation leading to cardiac arrhythmias, and severe gastrointestinal symptoms. Monitoring in patients with pre-existing liver, kidney, or heart conditions is recommended.