Biaxin (Clarithromycin) dosage. Clarithromycin comes as a tablet, an extended-release tablet, and a liquid form. The regular tablets and liquid forms are typically taken every 12 hours for seven to 14 days. The extended-release tablets are usually taken every 24 hours for seven to 14 days. You should begin to feel better after the first few days of treatment. For most infections, the recommended adult dose of clarithromycin is 250-500 milligrams (mg) of immediate release tablets twice daily, or 1,000 mg of extended- release tablets once daily for seven to 14 days.