Trough plasma imatinib concentrations are associated with responses to standard-dose imatinib in chronic myeloid leukemia and could improve its clinical management

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Background: Variable responses to imatinib in the treatment of myelogenous leukemia (CML) are incompletely understood. Previous studies focused on cellular mechanisms of resistance to imatinib. Another hypothesis for variable response lies in pharmacokinetic variability that may reduce drug exposure in patients receiving imatinib. Methods: Using high- performance liquid chromatography-tandem mass spectrometry, we assessed trough plasma imatinib concentrations at steady state (Cmin) in more than 150 CML patients. Major molecular response (MMR) was defined as a 3 logarithm reduction of BCR-ABL transcripts, quantified from peripheral blood using Q-RTPCR. In addition, suboptimal response criteria defined by the European Leukemianet were used to increase doses of imatinib. Results: i) we assessed Cmin in 85 CML patients and demonstated a correlation with imatinib doses (median values 813, 1,135, 1,709 ng/ml for respectively 300,400, 600 mg/day). ii) for 68 patients after at least one year's treatment mean Cmin were significantly higher in the group with MMR (34 patients) than in the group without (1,452.1±649.1 ng per milliliter vs. 869.3±427.5 ng per milliliter, P<0.001) whereas there was no difference in the imatinib daily dose. For Cmin and their discrimination potential for MMR, the area under receiver-operating characteristic curve was 0.775, with best sensitivity (76.5 percent) and specificity (70.6 percent) at a plasma threshold of 1,002 ng per milliliter. iii) dose escalation of imatinid, 400mg up to 600mg was proposed in 8 patients in suboptimal response (3 according to cytogenetic criteria and 5 according to molecular criteria). The median Cmin increase from 573 ng/ml [181–1,376] to 1,139 ng/ml [733–2,262] and 5 patients had a cytogenetic (n=3) or a molecular (n=2) response. Conclusions: Monitoring of imatinib plasma levels could be very useful for the management of CML patients, or should at least be checked in the case of treatment failure or suboptimal response or in patients nonadherent with imatinib or with a drug-drug interaction suspicion.

No significant financial relationships to disclose.

Design and first interim analysis of a randomized phase III trial comparing imatinib versus imatinib (IM) based combination therapies in newly diagnosed chronic myelogenous leukemia patients in chronic phase

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Background: Despite impressive results achieved with IM 400 mg/day alone, only a minority of pts reached a complete molecular remission at 12-month. Higher dose of IM or its combination with other therapies might improve molecular remission. Design of the trial: the 3 experimental arms are IM 400mg daily in combination with Peg-IFN-α2a (Peg-IFNα2a, 90 μg weekly) or with Ara-C (20 mg/m2/day, days 15–28 of 28-day cycles) or IM 600mg daily. The reference arm is IM 400mg daily. All pts (over 18 years of age with Bcr-Abl positive CML) receive IM 400 mg/day as monotherapy days 1–14 and then start the assigned regimen for at least 12 months. The endpoints are overall survival (primary), rate and duration of hematologic, cytogenetic and molecular responses and tolerability. An interim analysis of the first 636 pts at 1 year from randomization will allow evaluation of molecular response rates, one of the experimental arm being selected for further comparison with IM 400. An experimental arm would be selected if it increased the 4 log reduction response rate at 12-month by at least 20 percentage points, (15% to 35%), with an acceptable tolerability. Results: This evaluation is based on a cohort of 370 pts with a median time of observation of 16 months, recruited between 9/2003 and 9/2005. [median age 53 yrs (18–81); Sokal distribution: 38% of pts low, 38% intermediate, and 24% high]. At 1 month 80% of pts achieved complete hematologic response. At 12 months, 138 pts (72%) achieved a major cytogenetic response, being complete in 120 pts (63%). Grade 3/4 hematologic toxicity occurred in 8% of IM400 pts, 9% of IM600 pts, 41% of IM+IFN pts and 33% of IM+Ara-c pts respectively. Dose of Peg IFN was reduced in 16% of pts, 45 μg per week being well tolerated. Grade 3/4 non hematological toxicity occurred in 11% of IM400 pts, 16% of IM600 pts, 10% of IM+IFN pts (maily skin rash) and 11% of IM+Ara-c pts. Discontinuation of experimental treatment occurred in 17% of IM600 pts, 36% of IM+IFN pts and 16% of IM+Ara-c pts. Conclusion: This first analysis confirmed both feasibility of IM combinations and high response rates. However a substantial hematological toxicity requires a careful assessment of pts.

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