Drug Interactions between didanosine and moxifloxacin / triamcinolone

MONITOR CLOSELY: Concomitant administration of corticosteroids may potentiate the risk of tendinitis and tendon rupture associated with fluoroquinolone treatment. The mechanism is unknown. Tendinitis and tendon rupture have most frequently involved the Achilles tendon, although cases involving the rotator cuff (the shoulder), the hand, the biceps, and the thumb have also been reported. Some have required surgical repair or resulted in prolonged disability. Tendon rupture can occur during or up to several months after completion of fluoroquinolone therapy.

MANAGEMENT: Caution is recommended if fluoroquinolones are prescribed in combination with corticosteroids, particularly in patients with other concomitant risk factors (e.g., age over 60 years; recipient of kidney, heart, and/or lung transplant). Patients should be advised to stop taking the fluoroquinolone, avoid exercise and use of the affected area, and promptly contact their physician if they experience pain, swelling, or inflammation of a tendon. In general, fluoroquinolones should only be used to treat conditions that are proven or strongly suspected to be caused by bacteria and only if the benefits outweigh the risks.

ADJUST DOSING INTERVAL: Concomitant administration with didanosine buffered tablets or pediatric oral solution may reduce the oral bioavailability of moxifloxacin and other quinolone antibiotics. The mechanism is reduced quinolone absorption due to chelation with metallic cations from buffering agents and antacids used in certain formulations of didanosine. In 12 healthy volunteers, administration of an antacid containing aluminum hydroxide-magnesium hydroxide (900 mg-600 mg/10 mL dose) 4 hours before, simultaneously, and 2 hours after a single 400 mg dose of moxifloxacin reduced the relative bioavailability of moxifloxacin by 23%, 60%, and 26%, respectively. The pharmacokinetics of moxifloxacin have not been studied in combination with the various didanosine formulations, but significant reductions in bioavailability have been reported for ciprofloxacin, another quinolone, in interaction studies with didanosine.

MANAGEMENT: Moxifloxacin should be administered at least 4 hours before or 8 hours after didanosine buffered tablets or pediatric oral solution, and patients should be monitored for potentially decreased antimicrobial efficacy during concomitant therapy. Didanosine buffered powder for oral solution, which uses a citrate-phosphate buffer, and the delayed-release capsules, which are not buffered, are not expected to cause this interaction.