Clarithromycin

What is Clarithromycin?

Clarithromycin is a macrolide antibiotic used to treat various bacterial infections throughout the body. It belongs to the same class of antibiotics as erythromycin and azithromycin, but offers improved acid stability and better tissue penetration. This medication is commonly prescribed for respiratory tract infections, skin infections, and as part of combination therapy to treat stomach ulcers caused by H. pylori bacteria.

Uses

Clarithromycin is approved to treat several types of bacterial infections:

• Respiratory tract infections: Including pneumonia, bronchitis, and sinusitis caused by susceptible bacteria such as Streptococcus pneumoniae and Haemophilus influenzae
• Skin and soft tissue infections: Treating cellulitis, impetigo, and other bacterial skin infections, particularly those caused by Staphylococcus and Streptococcus species
• H. pylori eradication: Used in combination with other medications like proton pump inhibitors and amoxicillin to eliminate H. pylori bacteria that cause peptic ulcers
• Atypical mycobacterial infections: Treatment and prevention of Mycobacterium avium complex (MAC) infections, especially in immunocompromised patients
• Pharyngitis and tonsillitis: Alternative treatment for strep throat in patients who cannot take penicillin

How it works

Clarithromycin works by binding to the 50S ribosomal subunit of bacteria, which prevents them from producing essential proteins needed for survival and reproduction. This action is bacteriostatic, meaning it stops bacteria from growing and multiplying, allowing the body’s immune system to eliminate the infection. The drug concentrates well in tissues and cells, making it effective against both extracellular and some intracellular bacterial pathogens.

Side effects

Common side effects include:

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• Nausea and vomiting
• Diarrhea or loose stools
• Abdominal pain or cramping
• Metallic or bitter taste in mouth
• Headache
• Dizziness
• Skin rash or itching
• Fatigue or weakness

Serious side effects requiring immediate medical attention:

• Severe diarrhea or signs of C. difficile infection
• Heart rhythm abnormalities (QT prolongation)
• Severe allergic reactions with difficulty breathing or swelling
• Liver problems (yellowing of skin or eyes, dark urine)
• Hearing problems or ringing in ears

Warnings and precautions

• Heart conditions: Patients with existing heart rhythm disorders, low potassium or magnesium levels, or those taking medications that affect heart rhythm should use clarithromycin with extreme caution due to risk of dangerous arrhythmias
• Liver function: The medication is metabolized by the liver and can cause liver toxicity; patients with existing liver disease may need dose adjustments or alternative treatments
• Pregnancy and breastfeeding: Classified as pregnancy category C; should only be used when benefits outweigh risks, and caution is advised during breastfeeding as the drug passes into breast milk
• Myasthenia gravis: Can worsen muscle weakness in patients with this neuromuscular disorder
• Antibiotic resistance: Should only be used for confirmed or strongly suspected bacterial infections to prevent development of resistant bacteria

Interactions

Clarithromycin has numerous important drug interactions due to its effect on liver enzymes:

• Warfarin: Increases bleeding risk by enhancing anticoagulant effects
• Statins (atorvastatin, simvastatin): Increases statin levels, raising risk of muscle damage and rhabdomyolysis
• Digoxin: Increases digoxin levels, potentially causing dangerous heart rhythm problems
• Theophylline: Raises theophylline levels, increasing risk of toxicity and seizures
• Ergot alkaloids: Can cause dangerous vasoconstriction and ergot toxicity
• Triazolam and midazolam: Significantly increases sedative effects of these benzodiazepines
• Colchicine: Increases colchicine levels, potentially causing life-threatening toxicity
• Calcium channel blockers: May increase levels of medications like nifedipine and verapamil

Check interactions with the GMJ Interaction Checker

Dosage

Typical adult dosages vary depending on the infection being treated. For most respiratory and skin infections, the usual dose is 250-500 mg twice daily for 7-14 days. For H. pylori eradication, clarithromycin is typically prescribed as 500 mg twice daily for 10-14 days in combination with other medications. For MAC prevention in immunocompromised patients, 500 mg twice daily may be used long-term. Dosage adjustments are necessary for patients with severe kidney impairment. All dosing should be individualized and determined by a healthcare provider based on the specific infection, patient factors, and response to treatment.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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