Ibrutinib given at doses lower than the standard dose of 420 mg/day was associated with comparable overall survival and progression-free survival as the standard dose in patients with chronic lymphocytic leukemia (CLL), based on the results of a multicenter, retrospective study submitted as a poster at the annual meeting of the American Society of Clinical Oncology.
The initial findings indicate patients who experience toxicity on the 420 mg/day dosage can still do well on a slightly lower dose of ibrutinib, reported Colleen Timlin, Pharm.D., of the Hospital of the University of Pennsylvania, Philadelphia, and her associates.
At a median follow-up of 13.5 months, the median progression-free survival was 37.4 months in the standard dose group and the median progression-free survival had not been reached in the reduced-dose group. The median overall survival had not been reached in either group. The hazard ratio in the reduced-dose group was 1.2 for progression-free survival and 0.6 for overall survival; neither difference was statistically significant. Best overall response rate was 85% in the standard-dose group and 84% in the reduced-dose group.
The study included 197 patients, 37 of whom were shifted to reduced doses of ibrutinib within 3 months of initiating therapy at the recommended 420 mg/day dosage. For reduced-dose patients, the median ibrutinib dose was 4.3 mg/kg per day. The most common reasons for reducing the ibrutinib dose were gastrointestinal toxicity, bleeding, rash, cardiotoxicity, and renal insufficiency, the researchers said.
Most of the patients treated with doses less than 420 mg/day still maintained a dose of greater than 2.5 mg/kg per day, which assured adequate Bruton’s tyrosine kinase occupancy. The 420 mg/day dosage noted in the labeling was established, based on achievement of greater than 90% Bruton’s tyrosine kinase occupancy. Fewer patients achieve greater than 90% occupancy at lower doses, but lower doses may not translate into inferior outcomes.
Weight-based dosing should be considered in future studies and pharmacoeconomic analyses. Comparative analyses of toxicity profiles stratified by ibrutinib dose are underway, according to Dr. Timlin and her colleagues.
Dr. Timlin had no relevant disclosures. Several of her colleagues had multiple financial disclosures.
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