A 15 Hour Dosing-Collection Interval for Plerixafor Is at Least as Effective as the Standard 10 Hour Interval.

Plerixafor (formerly AMD3100) is a reversible CXCR4 inhibitor used to mobilize CD34+ cells for collection and use in hematopoietic transplant. Since beginning phase I trials, the drug has been given at 10 pm and collection initiated 10h later at 8 am. After recent FDA approval, we examined use of a dosing-collection interval of 15h (5 pm administration/8 am collection) for patient (pt) convenience. Here we compare results retrospectively from phase I and II trials at our institution using the 10h interval with post-approval collections using the 15h interval. We also evaluated prechemotherapy platelet (plt) count as a predictor of response to plerixafor+G-CSF.

We reviewed data for all pts (n=107) at our institution who received plerixafor using the 10h (n=79) and 15h (n=34) intervals. This group was reduced to only those who received 4 consecutive days of plerixafor (n=76), of which 67 had the 10h interval and 21 had the 15h interval. The age range of the 10h group was 30-79y (median 62) and the range of the 15h group was 45-78y (median 57). The primary disease in both groups was multiple myeloma, but included 2 NHL in the 10h group, and 5 NHL in the 15h group. Chemotherapy given prior to mobilization for both the 10h and 15h interval groups were similar and plerixafor was administered with G-CSF in all pts. CD34+ cells collected on days 1-4 were quantified by flow cytometry. Finally, some patients (n=9) underwent mobilization with plerixafor two or more times, of which 4 did so on both the 10h and 15h intervals. These instances were recorded as separate events. Prechemotherapy plt counts were also reviewed for each patient and subcategorized into 3 groups: <100, 100-150, and >150,000/uL. Mean CD34+ cells collected were compared between the plt subcategories for both the 10h and 15h groups.

The mean number of CD34+ cells collected for the 10h group on days 1-4 of plerixafor administration was 1.26, 1.04, 0.71, and 0.55 ×10e6 CD34+ cells/kg, respectively, with total average collection of 3.56 × 10e6 CD34+ cells/kg. For the 15h group, the average number of CD34+ cells collected on days 1-4 were 2.20, 1.61, 1.44, and 1.01 × 10e6 CD34+ cells/kg, respectively, with total average collection of 6.26 × 10e6 CD34+ cells/kg. The two groups were compared using two-tailed student's t-tests. There was no statistically significant difference between the quantity of CD34+ cells collected on days 1 or 2 for the 10h and 15h groups, however there was a statistically significant difference on days 3 and 4. On these latter two days, the 15h group collected a significantly higher number of CD34+ cells compared to the 10h group. The difference in average total collection for the two groups over all 4 days was statistically significant at an alpha level of 0.05 (p-value: 0.03). The different prechemotherapy plt groups were compared using one-way ANOVA statistical analysis. Within the 10h group the <100 group had the least amount collected (mean 2.46×10e6 CD34+/kg), the 100-150 had an intermediate amount (mean 3.30×10e6CD34+/kg), and the >150 group the most (4.30×10e6CD34+/kg; p-value 0.02). The same comparison within the 15h group showed similar findings but the number of patients in each subcategory was too small to be statistically significant.

Administration of plerixafor with the 15h interval (5 pm dosing/8 am collection) appears to be equivalent to the standard 10h interval with regard to quantity of CD34+ cells collected over the first 2 days, and is superior to the 10 h schedule if the collection continues for 4 days. Further, prechemotherapy plt count is predictive of ability to mobilize CD34+ cells with perixafor+G-CSF for the 10h interval, as has been previously shown by our group for G-CSF alone in a similar population. Additional pts are needed to demonstrate conclusively the same finding for the 15h dosing/collection interval.

No relevant conflicts of interest to declare.