Pharmacokinetics of the anti-androgenic drug flutamide in healthy stallions

Rapid equilibrium dialysis, ultrafiltration or ultracentrifugation? Evaluation of methods to quantify the unbound fraction of substances in plasma

In pharmacokinetics plasma protein binding (PPB) is a well-established parameter impacting drug disposition. The unbound fraction (f_u) is arguably regarded the effective concentration at the target site. Pharmacology and toxicology, increasingly use in vitro models. The translation of in vitro concentrations to in vivo doses can be supported by toxicokinetic modelling, e.g. physiologically based toxicokinetic models (PBTK). PPB of a test substance is an input parameter for PBTK. We compared three methods to quantify f_u: rapid equilibrium dialysis (RED), ultrafiltration (UF) and ultracentrifugation (UC) using twelve substances covering a wide range of Log P_ow (-0.1 to 6.8) and molecular weights (151 and 531 g/mol): Acetaminophen, Bisphenol A, Caffeine, Colchicine, Fenarimol, Flutamide, Genistein, Ketoconazole, α-Methyltestosterone, Tamoxifen, Trenbolone and Warfarin. After RED and UF separation, three polar substances (Log P_ow < 2) were largely unbound (f_u > 70%), while more lipophilic substances were largely bound (f_u < 33%). Compared to RED or UF, UC resulted in a generally higher f_u of lipophilic substances. f_u obtained after RED and UF were more consistent with published data. For half of the substances, UC resulted in f_u higher than the reference data. UF, RED and both UF and UC, resulted in lower f_u of Flutamide, Ketoconazole and Colchicine, respectively. For f_u quantifications, the separation method should be selected according to the test substance's properties. Based on our data, RED is suitable for a broader range of substances while UC and UF are suitable for polar substances.

Cholesterol-Based Nanovesicles Enhance the In Vitro Cytotoxicity, Ex Vivo Intestinal Absorption, and In Vivo Bioavailability of Flutamide

Critical adverse effects and frequent administration, three times per day, limit the use of flutamide (FLT) as a chemotherapeutic agent in the treatment of prostate cancer. Therefore, our research aimed to develop new cholesterol-based nanovesicles for delivering FLT to malignant cells in an endeavor to maximize its therapeutic efficacy and minimize undesired adverse effects. Draper–Lin small composite design was used to optimize the critical quality attributes of FLT-loaded niosomes and ensure the desired product quality. The influence of the selected four independent variables on mean particle size (Y₁), zeta potential (Y₂), drug entrapment efficiency (Y₃), and the cumulative drug release after 24 h (Y₄) was examined. The optimized nanovesicles were assessed for their in vitro cytotoxicity, ex-vivo absorption via freshly excised rabbit intestine as well as in vivo pharmacokinetics on male rats. TEM confirmed nanovescicles’ spherical shape with bilayer structure. Values of dependent variables were 748.6 nm, −48.60 mV, 72.8% and 72.2% for Y₁, Y₂, Y₃ and Y₄, respectively. The optimized FLT-loaded niosomes exerted high cytotoxic efficacy against human prostate cancer cell line (PC-3) with an IC₅₀ value of 0.64 ± 0.04 µg/mL whilst, it was 1.88 ± 0.16 µg/mL for free FLT. Moreover, the IC₅₀ values on breast cancer cell line (MCF-7) were 0.27 ± 0.07 µg/mL and 4.07 ± 0.74 µg/mL for FLT-loaded niosomes and free FLT, respectively. The permeation of the optimized FLT-loaded niosomes through the rabbit intestine showed an enhancement ratio of about 1.5 times that of the free FLT suspension. In vivo pharmacokinetic study displayed an improvement in oral bioavailability of the optimized niosomal formulation with AUC and C_max values of 741.583 ± 33.557 μg/mL × min and 6.950 ± 0.45 μg/mL compared to 364.536 ± 45.215 μg/mL × min and 2.650 ± 0.55 μg/mL for the oral FLT suspension. With these promising findings, we conclude that encapsulation of FLT in cholesterol-loaded nanovesicles enhanced its anticancer activity and oral bioavailability which endorse its use in the management of prostate cancer.