Alternative routes of drug administration: exposure of imatinib using different formulations.

Purpose: To explore the possibility of treating patients with alternative imatinib formulations.

Methods: Two patients were treated with different enteral en rectal imatinib formulations. During treatment plasma concentrations where measured to assure adequate exposure.

Results: The first patient received imatinib suspension through the duodenum tube. With a dose of 400 mg BID the patient had an imatinib plasma concentration of 750 µg/L. After increasing the dose to 600 mg BID the imatinib plasma concentration was 1500 µg/L (target GIST treatment > 1100 µg/L). Rectal administration of the tablet did not lead to sufficient plasma concentrations. The second had adequate exposure of imatinib both when the suspension was taken orally and through the tube (target CML treatment are > 1000 µg/L).

Conclusion: For patients able to swallow liquids, we prefer the suspended imatinib tablets (comparable to drug label). If patients have a duodenum tube the use of a suspension base with pulverized tablets could be an alternative. Based on the extremely low exposure found in case 1, we do not recommend rectal administration of tablets. We recommend the monitor plasma concentrations when off label dosing forms are used.