*Purpose: Neutropenia frequently occurs after solid organ transplantation (SOT) due to immunosuppression, antiviral prophylaxis, or viral infections. Immunosuppression reduction or antiviral prophylaxis minimization can lead to rejection or infection risk. Filgrastim (granulocyte colony-stimulating factor) is utilized to stimulate neutrophil production to decrease neutropenia and neutropenia-related events. There is limited data regarding filgrastim use for neutropenia management in SOT. A prior drug utilization evaluation at our institution identified a total of 259 filgrastim administrations in SOT recipients over a six-month period. This project investigated filgrastim efficacy in this cohort.

*Methods: A retrospective chart review was performed on SOT recipients receiving filgrastim from January – June 2017. Transplant types included: intestinal, kidney, liver, lung, heart, or multi-organ. Data collection included: filgrastim indication, average dose, dose range, ANC/WBC at start and end of therapy, peak ANC/WBC (up to one-week post-treatment), and mortality. Encounter was defined as an SOT recipient admission receiving filgrastim. The primary outcome was filgrastim treatment success (achieving an ANC >2 X 10³/L up to one-week post-treatment). Secondary outcomes included doses required to achieve treatment success, additional doses after treatment success, and mortality.

*Results: There were 99 encounters among 72 SOT recipients, with a total of 259 filgrastim administrations. Subjects per transplant service were: n=30 intestinal, n=9 kidney, n=14 liver, n=42 lung, n=2 heart, n=1 kidney/liver, n=1 heart/lung. Average filgrastim dose was 5.1 mcg/kg across all services, with the highest being 7.4 mcg/kg for intestinal transplant. Doses per encounter ranged from 1-12 (mean = 2.9 doses). Overall, 79% intestinal, 11% kidney, 25% liver, 54% lung, 100% heart, 100% kidney/liver, and 100% heart/lung recipients had an ANC <1.0 x 10³/L at filgrastim start. Treatment success was as follows: 97% intestinal, 67% kidney, 93% liver, 86% lung, 100% heart, 0% kidney/liver, 100% heart/lung. Mean doses to achieve treatment success were: 1.9 intestinal, 2.2 kidney, 2.2 liver, 2.1 lung, 1 heart, 1 kidney/liver, and 5 in heart/lung recipients. Some services continued filgrastim after achieving treatment success; intestinal (mean 1.3 doses) and lung (mean 0.3 doses). Deaths during filgrastim therapy occurred in n=4 (9.5%) lung and n=1 (11.1%) kidney subjects. All deaths were infection-related.

*Conclusions: Filgrastim was efficacious in treating neutropenic SOT recipients. The intestinal service has an opportunity to improve appropriate discontinuation after treatment success. While the majority of transplant services could be more judicious regarding filgrastim initiation, with all on-filgrastim mortality being infection-related, the proper timing of initiation (defined by an ANC cut-off) in SOT recipients warrants further investigation.

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