Pharmacometrics: The Already-Present Future of Precision Pharmacology

The use of mathematical modeling to represent, analyze, make predictions or providing information on data obtained in drug research and development has made pharmacometrics an area of great prominence and importance. The main purpose of pharmacometrics is to provide information relevant to the search for efficacy and safety improvements in pharmacotherapy. Regulatory agencies have adopted pharmacometrics analysis to justify their regulatory decisions, making those decisions more efficient. Demand for specialists trained in the field is therefore growing. In this review, we describe the meaning, history, and development of pharmacometrics, analyzing the challenges faced in the training of professionals. Examples of applications in current use, perspectives for the future, and the importance of pharmacometrics for the development and growth of precision pharmacology are also presented.

Columbus' egg: Oral drugs are absorbed in finite time

The infinite time of oral drug absorption was conceived from the first day of the birth of pharmacokinetics when H. Dost introduced the term pharmacokinetics in his book published in 1953. He adopted the function developed by H. Bateman back in 1908 for the decay of the nuclei isotopes to describe oral drug absorption as a first-order process. We unveiled this false hypothesis relying on common wisdom i.e. drugs are absorbed in finite time. This false assumption had dramatic effects on the evolution of oral pharmacokinetics but most importantly on the bioavailability and bioequivalence concepts and metrics. This work focuses on the finite absorption time (FAT) concept, the relevant Physiologically Based Finite Time (PBFTPK) models developed and their applications in oral pharmacokinetics, bioavailability and bioequivalence. The crux of the matter is that drug absorption from the gastrointestinal tract takes place under sink conditions because of the high blood flow rate in the vena cava. The termination of oral, pulmonary and intranasal drug absorption at a specific time point, calls for regulatory changes in bioavailability and bioequivalence studies in terms of the study design and metrics used for the bioequivalence assessment.

Population Pharmacokinetic Analysis of the Cathepsin K Inhibitor Odanacatib: Insights Into Intrinsic and Extrinsic Factor Effects on Exposure in Postmenopausal and Elderly Women

This analysis developed a population pharmacokinetic (PK) model for odanacatib, characterized demographic and concomitant medication covariates effect, and provided odanacatib exposure estimates for subjects in phase 2/3 studies. Data from multiple phase 1 (P005, P025, and P014), phase 2b (P004 and P022), and phase 3 (Long-Term Odanacatib Fracture Trial; P018) studies were pooled to create a data set of 1280 postmenopausal women aged 45 to 91 years (102 from phase 1, 514 from phase 2b, and 664 from phase 3) who received weekly oral odanacatib doses ranging from 3 to 100 mg. A 1-compartment model with first-order absorption, dose-dependent relative bioavailability (F1), and first-order elimination best described odanacatib PK. F1 decreased from the 100% reference bioavailability for a 3-mg oral dose to 24.5% for a 100-mg dose. Eight statistically significant covariates were included in the final PK model: body weight, age, race, and concomitant cytochrome P450 (CYP)3A inhibitors on apparent clearance; body weight on apparent central volume of distribution; and concomitant hydrochlorothiazide, high-fat breakfast, and a study effect on F1. All fixed- and random-effects parameters were estimated with good precision (%standard error of the mean ≤29.5%). This population PK analysis provides insights into intrinsic- and extrinsic-factor effects on odanacatib exposure in postmenopausal and elderly women with osteoporosis. The magnitude of the intrinsic-factor effects was generally modest (odanacatib exposure geometric mean ratios, 0.80-1.21) even in subjects aged >80 years, or in subsets with multiple combinations of factors.

Thorough QTc Evaluation and the Safety of Supratherapeutic Doses of Odanacatib in Healthy Subjects

Assessing risk for QTc interval prolongation in a thorough QTc study is a standard recommendation when evaluating new chemical entities. As part of the clinical development program for odanacatib, an oral selective inhibitor of cathepsin K previously in development for the treatment of osteoporosis, 2 clinical studies in healthy subjects assessed pharmacokinetics and overall safety (including potential for delayed ventricular repolarization) of a supratherapeutic dose. In study 1, subjects received a supratherapeutic dose regimen of odanacatib (300 mg on day 1, then daily multiple doses of 25 mg to day 21) or placebo. In study 2 (days 1-4), subjects received the odanacatib supratherapeutic dose regimen or moxifloxacin (positive control, single 400-mg dose on day 4; matching placebo for odanacatib/moxifloxacin) or placebo. All doses were administered with a high-fat meal. In study 1 (N = 12), the supratherapeutic dosing regimen achieved exposure ∼3.5-fold of the proposed therapeutic dose (50 mg once weekly) and was sufficiently well tolerated to permit assessment in the thorough QTc study (study 2). In study 2 (N = 116), the primary objective was placebo-corrected change from baseline in QTcF interval (Fridericia's correction), assessed by replicate electrocardiograms (12-lead Holter recordings; days -1 through 7). Supratherapeutic odanacatib dosing was not associated with increased risk of prolonged QT interval, unlike moxifloxacin (confirming assay sensitivity). Pooled safety data across both studies suggested that the safety profile of odanacatib at high exposures was similar to placebo, with a small clustering of oral cavity adverse events. Odanacatib was not associated with increased risk of prolonged QT interval.

Clinical and translational pharmacology of the cathepsin K inhibitor odanacatib studied for osteoporosis

Cathepsin K (CatK) is a cysteine protease abundantly expressed by osteoclasts and localized in the lysosomes and resorption lacunae of these cells. CatK is the principal enzyme responsible for the degradation of bone collagen. Odanacatib is a selective, reversible inhibitor of CatK at subnanomolar potency. The pharmacokinetics of odanacatib have been extensively studied and are similar in young healthy men, postmenopausal women and elderly men, and were qualitatively similar throughout Phase 1 development and in-patient studies. Following 3 weeks of 50 mg once weekly dosing the geometric mean area under the curve from 0 to 168 hours was 41.1 μM h, the concentration at 168 hours was 126 nM and the harmonic mean apparent terminal half-life was 84.8 hr. Odanacatib exposure increased in a less than dose proportional manner due to solubility limited absorption. It is estimated that approximately 70% of the absorbed dose of odanacatib is eliminated via metabolism, 20% is excreted as unchanged drug in the bile or faeces, and 10% is excreted as unchanged drug in the urine. The systemic clearance was low (approximately 13 mL/min). Odanacatib decreases the degradation of bone matrix proteins and reduces the efficiency of bone resorption with target engagement confirmed by a robust decrease in serum C-telopeptides of type 1 collagen (approximately 60%), urinary aminoterminal crosslinked telopeptides of type 1 collagen to creatinine ratio (approximately 50%) and total urine deoxypyridinoline/Cr (approximately 30%), with an increase in serum cross-linked carboxy-terminal telopeptide of type 1 collagen (approximately 55%). The 50-mg weekly dosing regimen evaluated in Phase 3 achieved near maximal reduction in bone resorption throughout the treatment period. The extensive clinical programme for odanacatib, together with more limited clinical experience with other CatK inhibitors (balicatib and ONO-5334), provides important insights into the clinical pharmacology of CatK inhibition and the potential role of CatK in bone turnover and mineral homeostasis. Key findings include the ability of this mechanism to: (i) provide sustained reductions in resorption markers, increases in bone mineral density, and demonstrated fracture risk reduction; (ii) be associated with relative formation-sparing effects such that sustained resorption reduction is achieved without accompanying meaningful reductions in bone formation; and (iii) lead to increases in osteoclast number as well as other osteoclast activity (including build-up of CatK enzyme), which may yield transient increases in resorption following treatment discontinuation and the potential for nonmonotonic responses at subtherapeutic doses.

Pharmacometrics and systems pharmacology for metabolic bone diseases

Mathematical modelling and simulation (M&S) of drug concentrations, pharmacologic effects and the (patho)physiologic systems within which they interact can be powerful tools for the preclinical, translational and clinical development of drugs. Indeed, the Prescription Drug User Fee Act (PDUFA VI), incorporated as part of the FDA Reauthorization Act of 2017 (FDARA), highlights the goal of advancing model-informed drug development (MIDD). MIDD can benefit development across many drug classes, including for metabolic bone diseases such as osteoporosis, cancer-related and numerous rare metabolic bone diseases; conditions characterized by significant morbidity and mortality. A drought looms in terms of the availability of new drugs to better treat these devastating diseases. This review provides an overview of several M&S approaches ranging from simple pharmacokinetic to integrated pharmacometric and systems pharmacology modelling. Examples are included to illustrate the use of these approaches during the development of several drugs for metabolic bone diseases such as bisphosphonates, denosumab, teriparatide and sclerostin inhibitors (romosozumab and blosozumab).

Identification of beagle food taking patterns and protocol for food effects evaluation on bioavailability

Food is a known primary role to the exposure of the drugs orally administered. Since each animal may have unique food taking pattern and it is difficult to manipulate the food taking to animals, there lacks rationalized protocol for the food effects in pre-clinic study. The objective of this study was to identify the beagle food taking patterns and demonstrate their effects on bioavailability in valsartan. Herein, four types of food taking patterns of beagle were identified via inter-day and intra-day analysis, and named as Persisting, Pulsing, Postponing, Pushing (“4P Modes”), respectively, which were also validated by principal component analysis (PCA). Interestingly, food intake resulted in a reduced area under the concentration-time curve (AUC_0–12h), maximum concentration (C_max) and absorption rate, whilst the reduction varied in “4P Modes” of food taking. General considerations in the design of experiment for food effect to the bioavailability in beagles have been established as: to recognize the food taking patterns in each animal, to confirm the inter-day stability of the food taking behaviors, to trace the food taking patterns in parallel with plasma sampling. In conclusion, the right animals with proper food taking patterns should be assessed and selected for pre-clinic bioavailability evaluations.

Odanacatib Pharmacokinetics Comparison Between Chinese and Non-Chinese Postmenopausal Women

Odanacatib (ODN), an oral selective inhibitor of cathepsin K, was an investigational agent previously in development for the treatment of osteoporosis. In this phase 1 open-label study, 12 healthy Chinese postmenopausal women received single-dose ODN 50 mg on day 1 and multiple-dose ODN 50 mg once weekly on days 15, 22, 29, and 36 under fasted conditions. Pharmacokinetic (PK) parameters were evaluated on days 1 and 36. Multiple-dose area under the concentration-time profile (AUC_0-168h ) and maximum plasma concentration (C_max ) were compared with historical data from 9 non-Chinese postmenopausal women who also received ODN 50 mg once weekly for 4 weeks. Median time to C_max (t_max ) was 3 and 4 hours following single- and multiple-dose administration, respectively. The arithmetic mean ± SD terminal half-life was 81.0 ± 14.0 and 106.7 ± 14.4 hours following single- and multiple-dose administration, respectively. Comparison of multiple-dose PK parameters showed that the geometric mean ratios (Chinese/non-Chinese) and 95%CIs for AUC_0-168h and C_max were 0.81 (0.55-1.19) and 0.87 (0.69-1.11), respectively. All adverse events were mild, none were serious, and none led to discontinuation. Single- and multiple-dose PKs of ODN 50 mg in Chinese postmenopausal women were generally similar to those previously reported in non-Chinese postmenopausal women.