Introduction: For over a decade, imatinib has been the first-line treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML). Doubts on the bioequivalence and bioavailability of emerging generic compounds have been expressed. Adequate imatinib plasma concentration ([IPC] ≥1000 μmol/L) is associated with a better chance of optimal treatment response in patients with CML. In this study, we compared the achieved IPCs between the branded compound and its 2 generic forms.
Patients and methods: IPCs were compared in 24 consecutive patients with CML in the first chronic phase who changed from branded to generic imatinib. The median age was 49 years (range, 22-76 years). Fifteen of them were male. Six patients were switched to Neopax, 13 to Imakrebin, and 5 patients received both generics consecutively. All compounds were used in an equivalent dose of 400 mg orally once daily for at least 1 month before plasma concentrations were measured. High-performance liquid chromatography was used to determine imatinib plasma concentration from a specimen collected 21 to 24 hours after the last dose.
Results: The median IPC achieved with branded imatinib was 1454 μmol/L (range, 485-2707 μmol/L) with 18 patients (75%) having IPC ≥ 1000 μmol/L. For Neopax and Imakrebin, median IPCs were 1717 μmol/L (range, 1249-3630 μmol/L) and 1458 μmol/L (range, 707-880 μmol/L), respectively, with 11 of 11 (100%) and 16 of 18 (89%) patients having IPC ≥ 1000 μmol/L. No significant difference in measured IPCs between all 3 compounds was found (P > .257).
Conclusion: When taken at equivalent doses, imatinib generics are bioequivalent and comparable in clinical efficacy and have the potential for substantial savings in the treatment cost for CML.
Keywords: Bioavailability; Clinical equivalency; Cost savings; Imatinib mesylate; Therapeutic drug monitoring.
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