Chelation Interactions

• Cations can form insoluble complexes with certain drugs, and prevent absorption

  • e.g., ddI + quinolones

• NB: ddI-EC does not contain buffer, and hence may be co-administered with quinolones

• Separate dosing times (2 hours before/6 hours after ddI/antacid dose)

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In order to avoid chelation interactions, drugs such as quinolones should be administered either 2 hours before or 6 hours after ingestion of antacids or ddI tablets.

Sahai J. Avoiding the ciprofloxacin-didanosine interaction [letter]. Ann Intern Med 1995;123:394-5.

However, it is important to make the distinction as to the specific formulation of ddI, since the enteric-coated capsule does not contain a buffer, and hence may be coadminstered with ciprofloxacin, as well as indinavir and ketoconazole.
Mummaneni V, Damle B, Kaul S, Knupp CA. Lack of effect of didanosine encapsulated enteric coated beadlet formulation on the pharmacokinetics of indinavir, ketoconazole, and ciprofloxacin in healthy subjects [abstract 1629]. 40th Interscience Conference on Antimicrobial Agents and Chemotherapy. Toronto, Canada, September 17-20, 2000.