Purpose Bone pain is a common side-effect of pegfilgrastim and can interfere with quality of life and treatment adherence. This study i nvestigated the impact of antihistamine prophylaxis on pegfilgrastim-induced bone pain. Methods This is a two stage enrichment trial design. Patients receiving an initial dose of pegfilgrastim after chemotherapy were enrolled into the observation stage (OBS). Those who developed significant back or leg bone pain (SP) were enrolled into the treatment stage (TRT) and randomized to daily loratadine 10 mg or placebo for 7 days. SP was defined by Brief Pain Inventory as back or leg pain score ≥ 5 and a 2 point increase after pegfilgrastim. The primary end-point of TRT was reduction of worst back or leg bone pain with loratadine, defined as 2 point decrease after treatment compared to OBS. Results 213 patients were included in the final analysis. Incidence of SP was 30.5%. The SP subset had a worse overall Functional Assessment of Cancer Therapy – Bone Pain score (33.9 vs. 51.7, p < 0.001) and a higher mean white blood cell count (15.4 vs. 8.4 K/cm3, p = 0.013) following pegfilgrastim than those without SP. 46 patients were randomized in the TRT. Benefit was 77.3% with loratadine and 62.5% with placebo (p = 0.35). Baseline NSAID use was documented in 4 patients (18.2%) in loratadine arm and 2 patients (8.3%) in placebo arm, with baseline non-NSAID use documented in 5 (22.7%) and 6 (25%) patients respectively. Eight additional patients used NSAIDS by day 8 compared to day 1 (6 in the loratadine and 2 in the placebo arm). A total of 6 additional patients used non-NSAIDS by day 8 compared to day 1 (4 in the loratadine and 2 in the placebo arm). Conclusions Administration of prophylactic loratadine does not decrease the incidence of severe bone pain or improve quality of life in a high-risk patient population.

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