clarithromycin
Biaxin, Biaxin XL

Available forms
Available by prescription only
Suspension: 125 mg/5 ml, 187.5 mg/5 ml, 250 mg/ 5 ml
Tablets: 250 mg, 500 mg
Tablets (extended-release): 500-mg tablets in bottles; 14-tablet blister package

Indications and dosages
 Pharyngitis or tonsillitis caused by Streptococcus pyogenes. Adults: 250 mg P.O. q 12 hours for 10 days.
Children: 15 mg/kg P.O. daily divided q 12 hours for 10 days.
 Acute maxillary sinusitis caused by Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis. Adults: 500 mg P.O. q 12 hours for 14 days. Or, two 500-mg extended-release tablets P.O. daily for 14 days.
Children: 15 mg/kg P.O. daily divided q 12 hours for 10 days.
 Acute exacerbations of chronic bronchitis caused by M. catarrhalis, S. pneumoniae, H. influenzae, or H. parainfluenzae. Adults: 250 mg P.O. q 12 hours for 7 to 14 days (for M. catarrhalis and S. pneumoniae only), or 500 mg P.O. q 12 hours for 7 days (up to 14 days for H. influenzae). Or, two 500-mg (extended-release) tablets P.O. daily for 7 days.
 Uncomplicated skin and skin-structure infections caused by Staphylococcus aureus or S. pyogenes. Adults: 250 mg P.O. q 12 hours for 7 to 14 days.
 Prophylaxis and treatment of disseminated infection from Mycobacterium avium complex. Adults: 500 mg P.O. b.i.d.
Children: 7.5 mg/kg P.O. b.i.d. up to 500 mg b.i.d.
 Acute otitis media caused by H. influenzae, M. catarrhalis, or S. pneumoniae. Children: 7.5 mg/kg P.O. q 12 hours up to 500 mg b.i.d.
 Helicobacter pylori eradication to reduce risk of duodenal ulcer recurrence. Adults: triple therapy, 500 mg Biaxin with 30 mg lansoprazole and 1 g amoxicillin, all given q 12 hours for 10 to 14 days, or 500 mg Biaxin with 20 mg omeprazole and 1 g amoxicillin, all given q 12 hours for 10 days. Or, dual therapy with 500 mg Biaxin q 8 hours and 40 mg omeprazole once daily for 14 days. Or, 500 mg Biaxin q 8 or 12 hours and 400 mg rantidine bismuth citrate q 12 hours for 14 days.
Children: 15 mg/kg/day divided q 12 hours for 10 days.
 Community-acquired pneumonia caused by Chlamydia pneumoniae, Mycoplasma pneumoniae, Streptococcus pneumoniae, Haemophilus influenzae, H. parainfluenzae, or Moraxella catarrhalis. Adults: 250 mg P.O. q 12 hours for 7 to 14 days. (for H. influenzae, duration of therapy is 7 days). Don’t use conventional tablets to treat pneumonia caused by H. parainfluenzae or M. catarrhalis. Or, two 500-mg (extended-release) tablets P.O. daily for 7 days for all listed organisms.
Children: 15 mg/kg P.O. daily divided q 12 hours for 10 days (for C. pneumoniae, M. pneumoniae, or S. pneumoniae only).
≡ Dosage adjustment. For patients with creatinine clearance of less than 30 ml/minute, reduce dose by 50% or double frequency interval.

Pharmacodynamics
Antibiotic action: Clarithromycin, a macrolide antibiotic, binds to the 50S subunit of bacterial ribosomes, blocking protein synthesis. It’s bacteriostatic or bactericidal, depending on the concentration.

Pharmacokinetics
Absorption: Rapidly absorbed from the GI tract; absolute bioavailability is about 50%. Although food slightly delays onset of absorption, clarithromycin may be taken without regard to meals because food doesn’t alter the total amount of drug absorbed.
Distribution: Widely distributed; because it readily penetrates cells, tissue concentrations are higher than plasma levels. Plasma half-life is dose-dependent; half-life is 3 to 4 hours at doses of 250 mg q 12 hours and increases to 5 to 7 hours at doses of 500 mg q 12 hours.
Metabolism: Clarithromycin’s major metabolite, 14-hydroxy clarithromycin, has significant antimicrobial activity. It’s about twice as active against H. influenzae as the parent drug.
Excretion: In patients taking 250 mg q 12 hours, about 20% is eliminated in the urine unchanged; this increases to 30% in patients taking 500 mg q 12 hours. The major metabolite accounts for about 15% of drug in the urine. Elimination half-life of the active metabolite is dose-dependent: 5 to 6 hours with 250 mg q 12 hours; 7 hours with 500 mg q 12 hours.

Contraindications and precautions
Contraindicated in patients hypersensitive to erythromycin or other macrolides who have cardiac abnormalities or electrolyte disturbances. Use cautiously in patients with impaired renal or hepatic function.

Interactions
Drug-drug. Carbamazepine, theophylline: May increase levels of these drugs. Monitor drug levels carefully.
Cyclosporine, phenytoin, triazolam: Decreases metabolism of these drugs. Monitor patient closely.
Digoxin: Increases digoxin levels. Monitor patient for signs of digoxin toxicity.
Dihydroergotamine, ergotamine: Causes acute ergot toxicity. Avoid use together.
Warfarin: Increases INR with other macrolides, and possibly with clarithromycin. Monitor patient closely.

Adverse reactions
CNS: headache.
GI: diarrhea, nausea, abnormal taste, dyspepsia, abdominal pain or discomfort.

Effects on lab test results
• May increase BUN, ALT, AST, alkaline phosphatase, bilirubin, GGT, and LDH levels.
• May increase PT and INR. May decrease WBC and platelet counts.

Overdose and treatment
No information available.

Special considerations
• Obtain specimen for culture and sensitivity tests before giving first dose. Therapy may begin pending test results.
• Reconstituted suspension shouldn’t be refrigerated; discard unused portion after 14 days.
• Drug may cause overgrowth of nonsusceptible bacteria or fungi. Monitor patient for signs and symptoms of superinfection.
Breast-feeding patients
• It isn’t known if drug appears in breast milk; however, other macrolides have been found in breast milk. Use with caution.
Pediatric patients
• Safety and efficacy in children younger than age 6 months haven’t been established.

Patient education
• Tell patient to take all of drug as prescribed, even if he feels better.
• Inform patient that he may take drug without regard to meals.
• Advise patient not to chew or crush extended-release tablets.
• Instruct patient to shake suspension well before use and not to refrigerate. Tell patient to discard unused portion after 14 days.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use