Mechanism of Action

Tbo-filgrastim is a human granulocyte colony-stimulating factor (G-CSF) produced by recombinant DNA technology. Tbo-filgrastim binds to G-CSF receptors and stimulates proliferation of neutrophils. G-CSF is known to stimulate differentiation commitment and some end-cell functional activation, which increases neutrophil counts and activity.

Pharmacodynamics

In the clinical trials of patients with cancer, the time to the ANCmax was between 3 to 5 days and returned to baseline by 21 days following completion of chemotherapy. In the healthy volunteer trials, doubling the tbo-filgrastim subcutaneous dose from 5 to 10 mcg/kg resulted in a 16-19% increase in the ANCmax and a 33-36% increase in the area under the effect curve for ANC.

Pharmacokinetics

In healthy subjects, the absolute bioavailability of 5 mcg/kg subcutaneous tbo-filgrastim was 33%. Increasing the dose of tbo-filgrastim from 5 to 10 mcg/kg in these healthy subjects resulted in an approximately 200% increase in both the maximum concentration (Cmax) and the area under the curve (AUC0-48h) of the drug.

In the clinical trials of patients with cancer, the AUC and Cmax were greater and more variable compared to healthy volunteers receiving the same dose of tbo-filgrastim subcutaneously. The median time to maximum concentration was between 4 to 6 hours and the median elimination half-life was between 3.2 to 3.8 hours. Accumulation was not observed after repeated dosing.

Pharmacokinetics in Specific Populations

Age: Not evaluated.

Gender: No gender-related differences were observed.

Renal Impairment: Mild renal impairment (creatinine clearance 60 - 89 mL/min) had no effect on tbo-filgrastim pharmacokinetics (N=11). The pharmacokinetic profile in patients with moderate and severe renal impairment has not been assessed.

Hepatic Impairment: The pharmacokinetic profile in patients with hepatic impairment has not been assessed.

QT/QTc Prolongation

The potential effects of tbo-filgrastim on the QTc interval were not adequately evaluated in clinical trials.

Clinical Studies

The efficacy of tbo-filgrastim was evaluated in a multinational, multicenter, randomized and controlled study Phase 3 study in 348 chemotherapy-naive patients with high-risk stage II, stage III, or stage IV breast cancer receiving doxorubicin (60 mg/m²) and docetaxel (75 mg/m²) comparing tbo-filgrastim to placebo and a non-US-approved filgrastim product as controls. The median age of the patients was 50 years (range 25 to 75 years) with 99% female and 86% Caucasian.

Tbo-filgrastim, placebo, and the non-US-approved filgrastim product were administered at 5 mcg/kg subcutaneously once daily beginning one day after chemotherapy for at least five days and continued to a maximum of 14 days or until an ANC of ≥ 10,000x10⁶/L after nadir was reached.

Tbo-filgrastim was superior to placebo in duration of severe neutropenia (DSN) with a statistically significant reduction in DSN (1.1 days vs. 3.8 days, p < 0.0001).

Last reviewed on RxList: 10/12/2012
This monograph has been modified to include the generic and brand name in many instances.