Adequate Neutrophil Responses and Non-Inferior Clinical Outcomes Can Be Achieved by a Two-Day Course of Low-Dose Filgrastim: A Retrospective Single Institution Experience

: Background Filgrastim is used in the setting of chemotherapy-induced neutropenia to stimulate recovery of bone marrow, which allows for further chemotherapy administration without delay. The recommended dose is 5 ug/kg. The commercially available vials of the drug come in two strengths; 300 ug and 480 ug. Due to these limitations in dosage formulations, it is a frequent occurrence to administer a lower dosage to patients weighing more than 60 kg, in whom the ideal dose would have been more than 300 ug but less than 480 ug. It is also a frequent practice to administer the drug for two consecutive days as it often leads to adequate response that will render patients eligible for their next cycle administration. Objective To determine whether a course of 300 ug of filgrastim administered daily for two consecutive days was as successful at reducing chemotherapy-induced neutropenia-related complications in patients with a higher weight (>60 kg) and hence receiving suboptimal dose as compared to those with weight less than 60 kg who are receiving the recommended dose. Methods We identified 91 patients from our facility with chemotherapy-induced neutropenia treated with 300 ug of filgrastim daily for two consecutive days, and we separated them into low, medium, and high weight groups. Multivariate logistic regression models examined correlations between outcomes (e.g., increases in absolute neutrophil count) and predictors (e.g., weight groups). Results The vast majority of encounters demonstrated rises in white blood cell (WBC) and absolute neutrophil count (ANC). Infection rates were not significantly different between low and medium weight groups (5% vs 0%; p = 0.1658), but the high weight group's infection rate was significantly higher than the medium weight group (5% vs 33%; p = 0.001). The high weight group did have an increased rate of febrile neutropenia as compared to medium and low weight groups, but these differences were not significant. Incidences of chemotherapy delay and dose reduction were comparable across the three weight groups. Limitations Retrospective study, small sample size, heterogeneous cancer sites and different chemotherapy regimens administered limit generalizability of findings. Conclusion Patients with weights <85 kg receiving a two-day course of 300 ug of filgrastim have similar neutropenia-related complication rates with a potential percent cost-savings of roughly 43%.