Prospective study of mobilization kinetics up to 18 hours after late-afternoon dosing of plerixafor.

Background: The current FDA-approved time interval between plerixafor dosing and apheresis initiation is approximately 11 hours, but this time interval is impractical for most care providers. Few studies have examined mobilization kinetics beyond 11 hours in multiple myeloma (MM) and non-Hodgkin's lymphoma (NHL) patients. Therefore, this study's intent was to analyze an interval of 17 to 18 hours between plerixafor dosing and apheresis initiation.

Study Design And Methods: In 11 patients with MM or NHL, 240 μg/kg plerixafor was administered at 5 p.m. on Day 4 of granulocyte-colony-stimulating factor (G-CSF) mobilization. Peripheral blood (PB) CD34+ and CD34+CD38- concentrations were enumerated every 2 hours until 7 a.m. and immediately before apheresis on Day 5, for a total interval time of 17 to 18 hours after plerixafor. Data were analyzed using mixed-model analysis of repeated measures and paired t testing.

Results: Ten of the 11 subjects achieved a CD34+ product count of more than 2 × 10(6) /kg with a single leukapheresis procedure. All 10 had a preplerixafor PB CD34+ concentration ([CD34+]) of at least 10/μL. PB [CD34+] was not different between 10 and 18 hours after plerixafor (p = 0.8). In contrast, PB CD34+CD38- concentrations significantly increased from 10 to 18 hours after plerixafor (p = 0.03).

Conclusions: In MM and NHL patients with adequate preplerixafor [CD34+], leukapheresis initiated 14 to 18 hours after plerixafor and G-CSF mobilization may not impair adequate CD34+ collection and may increase more primitive CD34+CD38- collection. In this subset of patients, late-afternoon dosing of plerixafor at 5 p.m. with initiation of next-day apheresis as late as 11 a.m. appears feasible without loss of efficacy.