Brief Report: Efficacy and Safety of Switching to Coformulated Elvitegravir, Cobicistat, Emtricitabine, and Tenofovir Alafenamide (E/C/F/TAF) in Virologically Suppressed Women.

BACKGROUND: The integrase inhibitor regimen [elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate (TDF)] demonstrated superior efficacy when compared with a protease inhibitor regimen [ritonavir-boosted atazanavir (ATV + RTV) and FTC/TDF] in 575 treatment-naive women at week 48. We investigated the efficacy, safety, and tolerability of switching to a TAF-based, single-tablet regimen containing elvitegravir, cobicistat, FTC, and tenofovir alafenamide (E/C/F/TAF) versus remaining on ATV + RTV plus FTC/TDF. METHODS: After completing the initial randomized, blinded phase, virologically suppressed (HIV-1 RNA <50 copies/mL) women on ATV + RTV plus FTC/TDF were rerandomized (3:1) to receive open-label E/C/F/TAF versus remaining on their current regimen. The primary end point was proportion of participants with plasma HIV-1 RNA <50 copies per milliliter at week 48 (U.S. FDA snapshot algorithm), with a prespecified noninferiority margin of 12%. Safety [adverse events (AEs)] and tolerability were also assessed. RESULTS: Of 575 women originally randomized and treated in the blinded phase, 159 were rerandomized to switch to E/C/F/TAF and 53 to remain on ATV + RTV plus FTC/TDF. At week 48, virologic suppression was maintained in 150 (94%) of women on E/C/F/TAF and 46 (87%) on ATV + RTV plus FTC/TDF [difference 7.5% (95% confidence interval -1.2% to 19.4%)], demonstrating noninferiority of E/C/F/TAF to ATV + RTV and FTC/TDF. Incidence of AEs was similar between groups; study drug-related AEs were more common with E/C/F/TAF (11% versus 4%). CONCLUSIONS: Switching to E/C/F/TAF was noninferior to continuing ATV + RTV plus FTC/TDF in maintaining virologic suppression and was well tolerated at 48 weeks.

Pharmacokinetics and pharmacodynamics of pegfilgrastim.

Pegfilgrastim is a sustained-duration form of filgrastim, a recombinant methionyl form of human granulocyte colony-stimulating factor (G-CSF), to which a 20 kDa polyethylene glycol molecule is covalently bound to the N-terminal methionine residue. Similar to filgrastim, pegfilgrastim increases the proliferation and differentiation of neutrophils from committed progenitor cells, induces maturation, and enhances the survival and function of mature neutrophils, resulting in dose-dependent increases in neutrophils. After subcutaneous administration, pegfilgrastim exhibits nonlinear pharmacokinetics and exposure to pegfilgrastim increases in more than a dose-proportional manner, suggesting that the clearance of pegfilgrastim decreases with increased dosing. Filgrastim is primarily eliminated by the kidney and neutrophils/neutrophil precursors; the latter presumably involves binding of the growth factor to the G-CSF receptor on the cell surface, internalization of the growth factor-receptor complexes via endocytosis, and subsequent degradation inside the cells. Pegylation of filgrastim renders renal clearance insignificant, which was demonstrated in bilaterally nephrectomized rats and confirmed in subjects with renal impairment. As a result, the neutrophil-mediated clearance is the predominant elimination pathway for pegfilgrastim. During chemotherapy-induced neutropenia, the clearance of pegfilgrastim is significantly reduced and the concentration of pegfilgrastim is sustained until onset of neutrophil recovery. Pegfilgrastim concentrations are sustained longer in patients with profound neutropenia. Evidence supports the use of a postnadir absolute neutrophil count (ANC) of ≥ 1 × 109/L as a surrogate marker threshold for the clearance of pegfilgrastim to subtherapeutic levels. After repeated administration of pegfilgrastim, the peak concentrations of pegfilgrastim decrease, likely due to increased neutrophil and neutrophil precursor mass. A pharmacokinetic-pharmacodynamic model was developed to describe the pharmacokinetic and ANC profiles of pegfilgrastim; the analysis supported that 100 µg/kg was an adequate weight-based dose of pegfilgrastim and predicted that 6 mg would be an optimal fixed dose of pegfilgrastim to simplify treatment. Data from a pivotal study confirmed that a once-per-chemotherapy-cycle injection of pegfilgrastim at 6 mg was as safe and effective as 11 daily injections of filgrastim at 5 µg/kg in reducing neutropenia and its complications in patients with breast cancer receiving four cycles of doxorubicin/docetaxel chemotherapy. Because of the highly efficient regulation of pegfilgrastim clearance via neutrophils and neutrophil precursors, a single fixed dose of pegfilgrastim can be given once per chemotherapy cycle in conjunction with a variety of myelosuppressive chemotherapy regimens.

Pharmacokinetics and pharmacodynamics of pegfilgrastim in subjects with various degrees of renal function.

A phase I study was conducted to evaluate the effects of renal function on the pharmacokinetics and pharmacodynamics (absolute neutrophil count [ANC]) of pegfilgrastim in nonneutropenic subjects. Thirty subjects categorized into 5 renal function groups (normal, mildly impaired, moderately impaired, severely impaired, and end-stage renal disease) received 1 subcutaneous injection of pegfilgrastim at 6 mg. The ANC profiles after pegfilgrastim administration were similar across different renal function groups. No discernable correlation between pharmacokinetic parameter values and degree of renal impairment was observed; the mean values ranged from 147 to 201 ng/mL for C(max) and from 7469 to 8513 ng x h/mL for AUC. Results suggest that the kidney has no important role in the elimination of pegfilgrastim. Therefore, no dosage adjustment for renal impairment is indicated for pegfilgrastim.

Serum pegfilgrastim concentrations during recovery of absolute neutrophil count in patients with cancer receiving pegfilgrastim after chemotherapy.

STUDY OBJECTIVE: To examine the serum concentrations of pegfilgrastim during recovery of absolute neutrophil count (ANC) in patients with cancer who received pegfilgrastim after chemotherapy. DESIGN: Retrospective analysis. DATA SOURCE: Data were pooled from seven pegfilgrastim registrational clinical trials: four open-label phase I or II studies and three randomized phase II or III studies. PATIENTS: A total of 370 patients with non-small cell lung cancer, Hodgkin's lymphoma, non-Hodgkin's lymphoma, or breast cancer. MEASUREMENTS AND MAIN RESULTS: Chemotherapy was given every 3 weeks, and pegfilgrastim was given once/chemotherapy cycle, 24 hours after chemotherapy completion. Data were available from 187 patients for the serum pegfilgrastim concentration analysis and from 319 patients for the ANC data analysis. Recovery of ANC to normal levels (>or= 1 x 10(3)/mm3) correlated well with the decline of pegfilgrastim concentrations to subtherapeutic levels; this inverse correlation was observed across different tumor types. By day 12 after pegfilgrastim administration, all patients experienced ANC recovery to normal levels, and none had a serum pegfilgrastim concentration above 2 ng/ml, considered the lowest concentration to elicit clinically meaningful granulopoiesis. After administration of pegfilgrastim, a steady postnadir recovery of the ANC to normal levels was noted, and postnadir peaks of 30 x 10(3)/mm3 or higher were observed in only three patients. CONCLUSION: Serum concentrations of pegfilgrastim were consistently cleared to subtherapeutic levels by day 12 after pegfilgrastim administration, and subtherapeutic pegfilgrastim levels were predicted by ANC recovery to 1 x 10(3)/mm3 or greater.