The recovery and biological activity of filgrastim after injection through a silicone rubber catheter were studied. Various volumes of filgrastim injection 300 micrograms/mL (0.17, 0.34, 0.51, 0.68, 0.85, and 1.0 mL) were injected through silicone rubber catheters and collected in glass vials to simulate intravenous bolus injections. The catheters were flushed with 3 mL of 5% dextrose injection before and after the injections. For some catheters, the procedure was repeated to simulate the administration of a second filgrastim dose through the same catheter. The theoretical filgrastim concentration in the expelled fluid was 16.1, 30.5, 43.6, 55.4, 66.2, or 75.0 micrograms/mL (corresponding to the filgrastim injection volumes). Filgrastim concentrations in expelled fluid were measured with an enzyme-linked immunosorbent assay, and biological activity was measured with a mitogenic cell-culture assay. There was > or = 10% loss of filgrastim after the first injection when the injection volume was 0.17, 0.34, or 0.68 mL. Mean drug recovery after the second filgrastim injection exceeded that after the first for all six volumes and was > or = 90% for five volumes. The recovered filgrastim retained all of its activity. A > or = 10% loss of filgrastim occurred for three of six volumes after one injection through a silicon rubber catheter. Recovery was higher after a second injection through the same catheter. Biological activity was not affected.