Drug General Information (ID: DDIF6C5B0P)
Drug Name			Didanosine		Drug Info		Norfloxacin		Drug Info
Drug Type		Small molecule				Small molecule
Therapeutic Class		Anti-Hiv Agents				Antibiotics
Structure

Mechanism of Didanosine-Norfloxacin Interaction (Severity Level: Moderate)
Complex formation Click to Show/Hide Mechanism Graph
Drug Name		Didanosine				Norfloxacin
Mechanism		Polyvalent cations				Binds to polyvalent cations
Key Mechanism Factor 1
		Factor Name		Chelation
		Factor Description		Chelation is a direct drug interaction that usually involves the formation of dimers or trimers, resulting in larger complexes and poorer absorption.
Mechanism Description		Decreased absorption of Didanosine due to formation of complexes caused by Norfloxacin

Recommended Action
Management		Norfloxacin should be administered at least 2 hours before or 2 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.

References
1	Campbell NR, Kara M, Hasinoff BB, Haddara WM, McKay DW "Norfloxacin interaction with antacids and minerals." Br J Clin Pharmacol 33 (1992): 115-6. [PMID: 1540482]
2	Deppermann KM, Lode H "Fluoroquinolones: interaction profile during enteral absorption." Drugs 45 Suppl 3 (1993): 65-72. [PMID: 7689454]
3	Knupp CA, Barbhaiya RH "A multiple-dose pharmacokinetic interaction study between didanosine (videx(r)) and ciprofloxacin (cipro(r)) in male subjects seropositive for HIV but asymptomatic." Biopharm Drug Dispos 18 (1997): 65-77. [PMID: 9008270]
4	Marchbanks CR "Drug-drug interactions with fluoroquinolones." Pharmacotherapy 13 (1993): s23-8. [PMID: 8474934]
5	Mizuki Y, Fujiwara I, Yamaguchi T "Pharmacokinetic interactions related to the chemical structures of fluoroquinolones." J Antimicrob Chemother 37 ( Suppl (1996): 41-55. [PMID: 8737124]
6	Nix DE, Wilton JH, Ronald B, Distlerath L, Williams VC, Norman A "Inhibition of norfloxacin absorption by antacids." Antimicrob Agents Chemother 34 (1990): 432-5. [PMID: 2334155]
7	Noyes M, Polk RE "Norfloxacin and absorption of magnesium-aluminum." Ann Intern Med 109 (1988): 168-9. [PMID: 3382110]
8	Polk RE "Drug-drug interactions with ciprofloxacin and other fluoroquinolones." Am J Med 87 (1989): s76-81. [PMID: 2686430]
9	Product Information. Noroxin (norfloxacin). Merck & Co, Inc, West Point, PA.
10	Product Information. Videx (didanosine). Bristol-Myers Squibb, Princeton, NJ.
11	Sahai J, Gallicano K, Oliveras L, Khaliq S, Hawley-Foss N, Garber G "Cations in the didanosine tablet reduce ciprofloxacin bioavailability." Clin Pharmacol Ther 53 (1993): 292-7. [PMID: 8453847]
12	Shiba K, Sakamoto M, Nakazawa Y, Sakai O "Effects of antacid on absorption and excretion of new quinolones." Drugs 49(Suppl 2) (1995): 360-1. [PMID: 8549362]
13	Damle BD, Mummaneni V, Kaul S, Knupp C "Lack of Effect of Simultaneously Administered Didanosine Encapsulated Enteric Bead Formulation (Videx EC) on Oral Absorption of Indinavir, Ketoconazole, or Ciprofloxacin." Antimicrob Agents Chemother 46 (2002): 385-91. [PMID: 11796346]