Central and peripheral lung deposition of fluticasone propionate dry powder inhaler formulations in humans characterized by population pharmacokinetics.

This study aimed to gain an in-depth understanding of the pulmonary fate of three experimental fluticasone propionate (FP) dry powder inhaler formulations which differed in mass median aerodynamic diameters (MMAD; A-4.5 µm, B-3.8 µm and C-3.7 µm; total single dose: 500 µg). Systemic disposition parameter estimates were obtained from published pharmacokinetic data after intravenous dosing to improve robustness. A biphasic pulmonary absorption model, with mucociliary clearance from the slower absorption compartment, and three systemic disposition compartments was most suitable. Rapid absorption, presumably from peripheral lung, had half-lives of 6.9 to 14.6 min. The peripherally deposited dose (12.6 µg) was significantly smaller for formulation A-4.5 µm than for the other formulations (38.7 and 39.3 µg for B-3.8 µm and C-3.7 µm). The slow absorption half-lives ranged from 6.86 to 9.13 h and were presumably associated with more central lung regions, where mucociliary clearance removed approximately half of the centrally deposited dose. Simulation-estimation studies showed that a biphasic absorption model could be reliably identified and that parameter estimates were unbiased and reasonably precise. Bioequivalence assessment of population pharmacokinetics derived central and peripheral lung doses suggested that formulation A-4.5 µm lacked bioequivalence compared to the other formulations both for central and peripheral doses. In contrast, the other fomulations were bioequivalent. Overall, population pharmacokinetics holds promise to provide important insights into the pulmonary fate of inhalation drugs, which are not available from non-compartmental analysis. This supports the assessment of the pulmonary bioequivalence of fluticasone propionate inhaled formulations through pharmacokinetic approaches, and may be helpful for discussions on evaluating alternatives to clinical endpoint studies.

A next-generation BRAF inhibitor overcomes resistance to BRAF inhibition in patients with BRAF-mutant cancers using pharmacokinetics-informed dose escalation.

RAF inhibitors have transformed treatment for BRAF V600-mutant cancer patients, but clinical benefit is limited by adaptive induction of ERK signaling, genetic alterations that induce BRAF V600 dimerization, and poor brain penetration. Next-generation pan-RAF dimer inhibitors are limited by narrow therapeutic index. PF-07799933 (ARRY-440) is a brain-penetrant, selective, pan-mutant BRAF inhibitor. PF-07799933 inhibited signaling in vitro, disrupted endogenous mutant-BRAF:wild-type-CRAF dimers, and spared wild-type ERK signaling. PF-07799933 ± binimetinib inhibited growth of mouse xenograft tumors driven by mutant BRAF that functions as dimers and by BRAF V600E with acquired resistance to current RAF inhibitors. We treated patients with treatment-refractory BRAF-mutant solid tumors in a first-in-human clinical trial (NCT05355701) that utilized a novel, flexible, pharmacokinetics-informed dose escalation design that allowed rapid achievement of PF-07799933 efficacious concentrations. PF-07799933 ± binimetinib was well-tolerated and resulted in multiple confirmed responses, systemically and in the brain, in BRAF-mutant cancer patients refractory to approved RAF inhibitors.

Oncology dose optimization paradigms: knowledge gained and extrapolated from approved oncology therapeutics.

There has been increasing attention to dose optimization in the development of targeted oncology therapeutics. The current report has analyzed the dose selection approaches for 116 new molecular entities (NMEs) approved for oncology indications by the US FDA from 2010 to August 2021, with the goal to extract learnings about the ways to select the optimal dose. The analysis showed that: (1) the initial label dose was lower than the maximum tolerated dose (MTD) or maximum studied dose (MSD) in Phase 1 for the majority of approved NMEs, and that the MTD approach is no longer the mainstay for dose selection; (2) there was no dose ranging or optimization beyond Phase 1 dose escalation for ~ 80% of the NMEs; (3) integrated dose/exposure-response analyses were commonly used to justify the dose selection; (4) lack of dose optimization led to dose-related PMRs/PMCs in 14% of cases, but 82% of these did not result in change of the initial label dose; and (5) depending on properties of the NME and specific benefit/risk considerations for the target patient population, there could be different dose selection paradigms leading to identification of the appropriate clinical dose. The analysis supports the need to incorporate more robust dose optimization during oncology clinical development, through comparative assessment of benefit/risk of multiple dose levels, over a wide exposure range using therapeutically relevant endpoints and adequate sample size. On the other hand, in certain cases, data from FIP dose escalation may be adequate to support the dose selection.

Can Pharmacokinetic Studies Assess the Pulmonary Fate of Dry Powder Inhaler Formulations of Fluticasone Propionate?

In the context of streamlining generic approval, this study assessed whether pharmacokinetics (PK) could elucidate the pulmonary fate of orally inhaled drug products (OIDPs). Three fluticasone propionate (FP) dry powder inhaler (DPI) formulations (A-4.5, B-3.8, and C-3.7), differing only in type and composition of lactose fines, exhibited median mass aerodynamic diameter (MMAD) of 4.5 µm (A-4.5), 3.8 µm (B-3.8), and 3.7 µm (C-3.7) and varied in dissolution rates (A-4.5 slower than B-3.8 and C-3.7). In vitro total lung dose (TLDin vitro) was determined as the average dose passing through three anatomical mouth-throat (MT) models and yielded dose normalization factors (DNF) for each DPI formulation X (DNFx = TLDin vitro,x/TLDin vitro,A-4.5). The DNF was 1.00 for A-4.5, 1.32 for B-3.8, and 1.21 for C-3.7. Systemic PK after inhalation of 500 µg FP was assessed in a randomized, double-blind, four-way crossover study in 24 healthy volunteers. Peak concentrations (Cmax) of A-4.5 relative to those of B-3.8 or C-3.7 lacked bioequivalence without or with dose normalization. The area under the curve (AUC0-Inf) was bio-IN-equivalent before dose normalization and bioequivalent after dose normalization. Thus, PK could detect differences in pulmonary available dose (AUC0-Inf) and residence time (dose-normalized Cmax). The differences in dose-normalized Cmax could not be explained by differences in in vitro dissolution. This might suggest that Cmax differences may indicate differences in regional lung deposition. Overall this study supports the use of PK studies to provide relevant information on the pulmonary performance characteristics (i.e., available dose, residence time, and regional lung deposition).

Four Decades of ß-Lactam Antibiotic Pharmacokinetics in Cystic Fibrosis.

The pharmacokinetics (PK) of ß-lactam antibiotics in cystic fibrosis (CF) patients has been compared with that in healthy volunteers for over four decades; however, no quantitative models exist that explain the PK differences between CF patients and healthy volunteers in older and newer studies. Our aims were to critically evaluate these studies and explain the PK differences between CF patients and healthy volunteers. We reviewed all 16 studies that compared the PK of ß-lactams between CF patients and healthy volunteers within the same study. Analysis of covariance (ANCOVA) models were developed. In four early studies that compared adolescent, lean CF patients with adult healthy volunteers, clearance (CL) in CF divided by that in healthy volunteers was 1.72 ± 0.90 (average ± standard deviation); in four additional studies comparing age-matched (primarily adult) CF patients with healthy volunteers, this ratio was 1.46 ± 0.16. The CL ratio was 1.15 ± 0.11 in all eight studies that compared CF patients and healthy volunteers who were matched in age, body size and body composition, or that employed allometric scaling by lean body mass (LBM). Volume of distribution was similar between subject groups after scaling by body size. For highly protein-bound ß-lactams, the unbound fraction was up to 2.07-fold higher in older studies that compared presumably sicker CF patients with healthy volunteers. These protein-binding differences explained over half of the variance for the CL ratio (p < 0.0001, ANCOVA). Body size, body composition and lower protein binding in presumably sicker CF patients explained the PK alterations in this population. Dosing CF patients according to LBM seems suitable to achieve antibiotic target exposures.

First population pharmacokinetic analysis showing increased quinolone metabolite formation and clearance in patients with cystic fibrosis compared to healthy volunteers.

Understanding the pharmacokinetics in patients with cystic fibrosis (CF) is important for dosing. For antibiotics with extensive metabolism, however, a comparison of metabolite formation and elimination between patients with CF and healthy volunteers has never been performed via population modeling. We aimed to compare the population pharmacokinetics of fleroxacin and its N­oxide and demethyl metabolites between patients with CF and healthy volunteers. Our analysis included eleven adult patients with CF and twelve healthy volunteers who received 800 mg fleroxacin as a single oral dose followed by five doses every 24 h from a previously published study. All plasma concentrations and amounts in urine for fleroxacin and its metabolites were simultaneously modelled. The estimates below accounted for differences in body size and body composition via allometric scaling by lean body mass. Oral absorption was slower in patients with CF than in healthy volunteers. For fleroxacin, the population mean in patients with CF divided by that in healthy volunteers was 1.12 for renal clearance, 1.01 for linear nonrenal clearance, 0.83 for saturable exsorption clearance into intestine, and 0.81 for volume of distribution. The formation clearances of N­oxide fleroxacin and N­demethylfleroxacin were 0.520 L/h and 0.496 L/h in patients with CF; these formation clearances were 0.378 L/h and 0.353 L/h in healthy volunteers. Renal clearance in patients with CF divided by that in healthy volunteers was 1.53 for N­oxide fleroxacin and 1.70 for N­demethyl fleroxacin. Allometric scaling by lean body mass best explained the variability. While fleroxacin pharmacokinetics was comparable, both formation and elimination clearances of its two metabolites were substantially larger in patients with CF compared to those in healthy volunteers.

A need to revisit clinical breakpoints of tigecycline: effect of atypical non-linear plasma protein binding.

Tigecycline is highly active against various drug-resistant bacteria. The US Food and Drug Administration (FDA) recently issued a black box warning for tigecycline owing to an associated increase in all-cause mortality. Clinical breakpoints of antibiotics are vital in susceptibility testing of pathogens for the selection of antibiotic therapy; however, no consensus exists between different committees on the clinical breakpoints of tigecycline. Of note, tigecycline exhibits atypical non-linear plasma protein binding (PPB) behaviour, and the pivotal probability of target attainment (PTA) analysis for the determination of clinical breakpoints did not account for the PPB of tigecycline. In this work, the PTA analysis was performed with consideration of atypical non-linear PPB behaviour of tigecycline. A model describing atypical non-linear PPB was developed and validated. Monte Carlo simulations were performed to determine the target ratio of area under the free drug concentration-time curve to minimum inhibitory concentration (fAUC/MIC) for Escherichia coli and, subsequently, PTA analyses were performed. The target fAUC/MIC ratio for E. coli was determined as 2.05, whilst the target AUC/MIC ratio was 6.96. The PTA analyses suggest a lower clinical breakpoint of tigecycline against E. coli. This finding suggests that there is a need to revisit the current clinical breakpoints of tigecycline.