Purpose: The short half-life of filgrastim allows for modification in the dose or duration of prophylaxis to limit inconvenience, adverse effects, and cost. The objectives of this study were to characterize and compare pain and neutropenic events between filgrastim and pegfilgrastim.
Methods: A prospective, observational study was performed. Eligible patients had non-metastatic breast cancer and were to receive adjuvant or neo-adjuvant chemotherapy with prophylaxis for febrile neutropenia. The prophylaxis used was a fixed-dose regimen of filgrastim 300 μg subcutaneously once daily for 7 days or pegfilgrastim 6 mg subcutaneously for 1 day. Participants completed a pain diary once a day for 14 days commencing the evening of the patient's first chemotherapy. Telephone interviews occurred at two instances within 2 weeks after their first treatment. The primary endpoints of this study were the difference in pain and incidences of neutropenia. Muscle pain, pain burden, and potential risk factors for pain were also explored.
Results: A total of 142 women were enrolled, 94 with pegfilgrastim and 48 with filgrastim. Filgrastim was associated with worse joint and muscle pain compared to pegfilgrastim. Joint pain was present in 38 and 26 % of diary entries for filgrastim and pegfilgrastim, respectively (p = 0.009). The mean AUC for joint pain score across 14 days, normalized to 100, were 6.0 for pegfilgrastim and 8.6 for filgrastim in patients receiving non-docetaxel chemotherapy and 14.6 for pegfilgrastim and 21.5 for filgrastim in patients receiving docetaxel-based chemotherapy (p = 0.037). Muscle pain patterns and frequencies were similar to joint pain. There were no statistical differences in febrile neutropenia and neutropenic events.
Conclusions: Both filgrastim and pegfilgrastim caused significant pain burden. A fixed-dose regimen of filgrastim may be effective, but offers no advantage to minimize muscle or joint pain and, in fact, appears to cause greater and more frequent pain.