Application of the Finite Absorption Time (F.A.T.) Concept in the Assessment of Bioequivalence.

PURPOSE: Το formulate a methodology for the assessment of bioequivalence using metrics, which are based on the physiologically sound F.A.T. METHODS: The equations of the physiologically based finite time pharmacokinetic models for the one-and two-compartment model with one and two input stages of absorption were solved to derive metrics for the extent and rate of absorption. Simulated data were used to study the proper way for the estimation of metrics. A bioequivalence study was analyzed using these metrics. RESULTS: The rate of drug absorption was found to be equal to the slope of the amount absorbed versus time curve. The amount of drug absorbed at the end of the absorption process, corresponding to the blood concentration at F.A.T. is an indicator of the extent of absorption. The plot of the ratio test/reference of the simulated data for the amount absorbed as a function of time becomes constant beyond the end of drug absorption from the formulation exhibiting the longer absorption. The assessment of the bioequivalence study was based on the slope of the amount absorbed versus time curve for the rate of absorption, while the estimate for the constant ratio test/reference for the amount absorbed was used for the assessment of extent of absorption. CONCLUSIONS: The assessment of rate in bioequivalence studies can be based on the estimation of slope of the percent absorbed versus time curve while the constant ratio test/reference for the amount of drug absorbed is an indicator of the extent of absorption.

IVIVC Revised.

PURPOSE: To revise the IVIVC considering the physiologically sound Finite Absorption Time (F.A.T.) and Finite Dissolution Time (F.D.T.) concepts. METHODS: The estimates τ and τd for F.A.T. and F.D.T., respectively are constrained by the inequality τd ≤ τ; their relative magnitude is dependent on drug's BCS classification. A modified Levy plot, which includes the time estimates for τ and τd was developed. IVIVC were also considered in the light of τ and τd estimates. The modified Levy plot of theophylline, a class I drug, coupled with the rapid (30 min) and very rapid (15 min) dissolution time limits showed that drug dissolution/absorption of Class I drugs takes place in less than an hour. We reanalyzed a carbamazepine (Tegretol) bioequivalence study using PBFTPK models to reveal its complex absorption kinetics with two or three stages. RESULTS: The modified Levy plot unveiled the short time span (~ 2 h) of the in vitro dissolution data in comparison with the duration of in vivo dissolution/absorption processes (~ 17 h). Similar results were observed with the modified IVIVC plots. Analysis of another set of carbamazepine data, using PBFTPK models, confirmed a three stages absorption process. Analysis of steady-state (Tegretol) data from a paediatric study using PBFTPK models, revealed a single input stage of duration 3.3 h. The corresponding modified Levy and IVIVC plots were found to be nonlinear. CONCLUSIONS: The consideration of Levy plots and IVIVC in the light of the F.A.T. and F.D.T. concepts allows a better physiological insight of the in vitro and in vivo drug dissolution/absorption processes.

Coupling Drug Dissolution with BCS.

PURPOSE: The purpose of this study is to develop a Temporal Biopharmaceutic Classification System (T-BCS), linking Finite Dissolution Time (F.D.T.) and Mean Dissolution Time (M.D.T.) for Class I/III drugs and Mean Dissolution Time for saturation (M.D.T.s.) for Class II/IV drugs. METHODS: These parameters are estimated graphically or by fitting dissolution models to experimental data and coupled with the dose-to-solubility ratio (q) for each drug normalized in terms of the actual volume of dissolution medium (900 mL). RESULTS: Class I/III drugs consistently exhibited q values less than 1, aligning with expectations based on their solubility, while some Class II/IV drugs presented a deviation from anticipated q values, with observations of q < 1. This irregularity was rendered to the dissolution volume of 250 mL used for biopharmaceutical classification purposes instead of 900 mL applied as well as the dual classification of some sparingly soluble drugs. Biowaivers were also analyzed in terms of M.D.T., F.D.T. estimates and the regulatory dissolution time limits for rapidly and very-rapidly dissolved drugs. CONCLUSIONS: The T-BCS is useful for establishing correlations and assessing the magnitude of M.D.T., F.D.T., or M.D.T.s. for inter- and intra-class comparisons of different drugs and provide relationships between these parameters across all the models that were utilized.

Revamping Biopharmaceutics-Pharmacokinetics with Scientific and Regulatory Implications for Oral Drug Absorption.

PURPOSE: The Wagner-Nelson and Loo-Riegelman methods developed in the 1960s and used since for the construction of percent of drug absorbed as a function of time as well as in in vitro in vivo correlations are re-considered in the light of the physiologically sound Finite Absorption Time (F.A.T.) concept developed recently. METHODS: The classical equations for the percentage of drug absorption as a function of time were modified by taking into account the termination of drug absorption at F.A.T., replacing the parameters associated with the assumption of infinite drug absorption. RESULTS: Mathematical analysis using the relevant Physiologically Based Pharmacokinetic Finite Time (PBFTK) models assuming one- or two-compartment drug disposition, revealed that the modified %absorbed versus time curves are of bilinear type with an ascending limb intersecting the horizontal line at F.A.T. A computer-based methodology is described for the estimation of F.A.T. from experimental data. More than one linear ascending limb is found when more than one absorption phase is operating. Experimental data were analyzed and the estimates for F.A.T were found to be similar to those derived from nonlinear regression analysis using PBFTPK models. CONCLUSION: These results place an end to the routinely reported exponential %absorbed versus time curves prevailing in biopharmaceutics-pharmacokinetics since their inception in the'60 s. These findings point to the use of the F.A.T. concept in drug absorption research and regulatory guidelines such as deconvolution techniques for the assessment of drug input rate, stochastic mean absorption time calculations, population analyses, in vitro in vivo correlations and bioequivalence guidelines.

Re-examining Naloxone Pharmacokinetics After Intranasal and Intramuscular Administration Using the Finite Absorption Time Concept.

BACKGROUND AND OBJECTIVES: Naloxone for opioid overdose treatment can be administered by intravenous injection, intramuscular injection, or intranasal administration. Published data indicate differences in naloxone pharmacokinetics depending on the route of administration. The aim of this study was to analyze pharmacokinetic data in the same way that we recently successfully applied the concept of the finite absorption time in orally administered drug formulations. METHODS: Using the model equations already derived, we performed least squares analysis on 24 sets of naloxone concentration in the blood as a function of time. RESULTS: We found that intramuscular and intranasal administration can be described more accurately when considering zero-order absorption kinetics for finite time compared with classical first order absorption kinetics for infinite time. CONCLUSIONS: One-compartment models work well for most cases. Two-compartment models provide better details, but have higher parameter uncertainties. The absorption duration can be determined directly from the model parameters and thus allow an easy comparison between the ways of administration. Furthermore, the precise site of injection for intramuscular delivery appears to make a difference in terms of the duration of the drug absorption.

Physiologically based Pharmacokinetic Models under the Prism of the Finite Absorption Time Concept.

To date, mechanistic modeling of oral drug absorption has been achieved via the use of physiologically based pharmacokinetic (PBPK) modeling, and more specifically, physiologically based biopharmaceutics model (PBBM). The concept of finite absorption time (FAT) has been developed recently and the application of the relevant physiologically based finite time pharmacokinetic (PBFTPK) models to experimental data provides explicit evidence that drug absorption terminates at a specific time point. In this manuscript, we explored how PBBM and PBFTPK models compare when applied to the same dataset. A set of six compounds with clinical data from immediate-release formulation were selected. Both models resulted in absorption time estimates within the small intestinal transit time, with PBFTPK models generally providing shorter time estimates. A clear relationship between the absorption rate and the product of permeability and luminal concentration was observed, in concurrence with the fundamental assumptions of PBFTPK models. We propose that future research on the synergy between the two modeling approaches can lead to both improvements in the initial parameterization of PBPK/PBBM models but to also expand mechanistic oral absorption concepts to more traditional pharmacometrics applications.

The Finite Absorption Time (FAT) concept en route to PBPK modeling and pharmacometrics.

The concept of Finite Absorption Time (FAT) for oral drug administration is set to affect pharmacokinetic analyses, Physiologically-based Pharmacokinetics simulations, and Pharmacometrics.

Re-writing Oral Pharmacokinetics Using Physiologically Based Finite Time Pharmacokinetic (PBFTPK) Models.

PURPOSE: To develop physiologically based finite time pharmacokinetic (PBFTPK) models for the analysis of oral pharmacokinetic data. METHODS: The models are based on the passive drug diffusion mechanism under the sink conditions principle. Up to three drug successive input functions of constant rate operating for a total time τ are considered. Differential equations were written for all these models assuming linear one- or two-compartment-model disposition. The differential equations were solved and functions describing the concentration of drug as a function of time for the central and the peripheral compartment were derived. The equations were used to generate simulated data and they were also fitted to a variety of experimental literature oral pharmacokinetic data. RESULTS: The simulated curves resemble real life data. The end of the absorption processes τ is either equal to tmax or longer than tmax at the descending portion of the concentration time curve. Literature oral pharmacokinetic data of paracetamol, ibuprofen, almotriptan, cyclosporine (a total of four sets of data), and niraparib were analyzed using the PBFTPK models. Estimates for τ corresponding to a single or two or three different in magnitude input rates were derived along with the other model parameters for all data analyzed. CONCLUSIONS: The PBFTPK models are a powerful tool for the analysis of oral pharmacokinetic data since they rely on the physiologically sound concept of finite absorption time.

Revising Pharmacokinetics of Oral Drug Absorption: II Bioavailability-Bioequivalence Considerations.

PURPOSE: To explore the application of the parameters of the physiologically based finite time pharmacokinetic (PBFTPK) models subdivided in first-order (PBFTPK)1 and zero-order (PBFTPK)0 models to bioavailability and bioequivalence. To develop a methodology for the estimation of absolute bioavailability, F, from oral data exclusively. METHODS: Simulated concentration time data were generated from the Bateman equation and compared with data generated from the (PBFTPK)1 and (PBFTPK)0 models. The blood concentration Cb(τ) at the end of the absorption process τ, was compared to Cmax; the utility of [Formula: see text] and [Formula: see text] in bioequivalence assessment was also explored. Equations for the calculation of F from oral data were derived for the (PBFTPK)1 and (PBFTPK)0 models. An estimate for F was also derived from an areas proportionality using oral data exclusively. RESULTS: The simulated data of the (PBFTPK)0 models exhibit rich dynamics encountered in complex drug absorption phenomena. Both (PBFTPK)1 and (PBFTPK)0 models result either in Cmax = Cb(τ) or Cmax > Cb(τ) for rapidly- and not rapidly-absorbed drugs, respectively; in the latter case, Cb(τ) and τ are meaningful parameters for drug's rate of exposure. For both (PBFTPK)1 and (PBFTPK)0 models, [Formula: see text] or portions of it cannot be used as early exposure rate indicators. [Formula: see text] is a useful parameter for the assessment of extent of absorption for very rapidly absorbed drugs. An estimate for F for theophylline formulations was found close to unity. CONCLUSION: The (PBFTPK)1 and (PBFTPK)0 models are more akin to in vivo conditions. Estimates for F can be derived from oral data exclusively.

Interpreting airborne pandemics spreading using fractal kinetics' principles.

Introduction  The reaction between susceptible and infected subjects has been studied under the well-mixed hypothesis for almost a century. Here, we present a consistent analysis for a not well-mixed system using fractal kinetics' principles.  Methods  We analyzed COVID-19 data to get insights on the disease spreading in absence/presence of preventive measures. We derived a three-parameter model and show that the "fractal" exponent h of time larger than unity can capture the impact of preventive measures affecting population mobility.  Results  The h=1 case, which is a power of time model, accurately describes the situation without such measures in line with a herd immunity policy. The pandemic spread in four model countries (France, Greece, Italy and Spain) for the first 10 months has gone through four stages: stages 1 and 3 with limited to no measures, stages 2 and 4 with varying lockdown conditions. For each stage and country two or three model parameters have been determined using appropriate fitting procedures. The fractal kinetics model was found to be more akin to real life.  Conclusion  Model predictions and their implications lead to the conclusion that the fractal kinetics model can be used as a prototype for the analysis of all contagious airborne pandemics.

Thyroid-stimulating hormone is not the primary regulator of thyroid development in euthyroid children and adolescents living in an iodine-replete area.

OBJECTIVES: It is known that there are multiple factors which can affect thyroid gland development during childhood and adolescence. Our aim was to investigate this issue by examining the relationships between age, sex, several anthropometric parameters, pubertal status, thyroid function tests, and iodine intake status with thyroid volume (TV) in children and adolescents. STUDY DESIGN: This was a cross-sectional field study conducted in 11 representative cities and villages of Uzbekistan. Six hundred and ten children and adolescents participated. Anthropometric indices and TV were estimated. In addition, thyroid function tests (TFTs) and urinary iodine excretion (UIE) measures were obtained. RESULTS: Median UIE was 151 µg/L, thus the studied areas were iodine-sufficient. TFTs fluctuated in both genders during childhood and adolescence and the thyroid growth spurt was observed, in both sexes, at the ages of 12 and 13 years, which coincided with the age of menarche in girls. Thyroid volume was positively correlated with body surface area (BSA) (r = 0.800, p < 0.001), age (r = 0.780, p < 0.001), fat-free mass (FFM) (r = 0.797, p < 0.001) and negatively correlated with serum TSH (r = -0.154, p = 0.05). No association between thyroid volume and UIE was observed. CONCLUSIONS: In euthyroid children and adolescents living in iodine-replete areas, thyroid gland development appears to follow the pattern of linear growth and displays a growth spurt at the onset of puberty, probably due to the abrupt increase of circulating sex steroids. At this age, TSH does not appear to be the main regulator of thyroid gland development.

The effect of prolonged aerobic exercise on serum adipokine levels during an ultra-marathon endurance race.

OBJECTIVE: To evaluate the effect of prolonged intensive aerobic exercise and acute energy deficit (180 km ultra-marathon race) on serum leptin, adiponectin, resistin and visfatin levels and their association and interaction with serum cortisol and insulin levels in highly trained ultra-endurance runners. DESIGN: The study included 17 highly trained ultra-endurance male athletes (mean age 51.29±6.84 years and body mass index (ΒΜΙ) 23.51±1.90) participating in the 5th Olympian Race held in Greece on May 2010. Anthropometric values were assessed; Serum cortisol, insulin, leptin, adiponectin, resistin and visfatin levels were measured at baseline, post-exercise and ~20 hours after the end of the race. RESULTS: All hormonal values of the post-exercise and recovery status were corrected for plasma volume changes. The estimated energy deficit during the ultra-endurance event was about 5000 Kcal. At the end of the race serum resistin levels were elevated (p<0.001) and serum leptin levels were reduced (p<0.001) and failed to reach pre-exercise levels, although showing a tendency towards restoration. No significant changes were noted in serum adiponectin and visfatin levels. CONCLUSIONS: Ultra-endurance aerobic exercise and acute negative energy balance lead to an up-regulation of serum resistin levels and a down-regulation of serum leptin levels.

Growth velocity and final height in elite female rhythmic and artistic gymnasts.

PURPOSE: The aim of this study was to determine the impact of intensive training on adult final height in elite female rhythmic and artistic gymnasts. METHODS: The study included 215 rhythmic gymnasts (RG) and 113 artistic gymnasts (AG). RESULTS: AG were below the 50th percentile, while RG were taller than average. Final adult height was lower than target height in AG, while in RG, it exceeded target height. AG started training earlier than RG (p<0.001) and reported lower intensity of training (p<0.001). RG were taller than AG, with higher target height, greater Δ final height-target height and lower body fat and BMI (p<0.001). Using multiple regression analysis, the main factors influencing final height were weight SDS (p<0.001), target height SDS (p<0.001) and age of menarche (p<0.001) for RG, and weight SDS (p<0.001) and target height SDS (p<0.001) for AG. CONCLUSION: In both elite female RG and AG, genetic predisposition to final height was not disrupted and remained the main force of growth. Although in elite RG genetic predisposition for growth was fully preserved, in elite female AG final adult height falls shorter than genetically determined target height, though within the standard error of prediction.

Significant modification of the I(-)3 Lewis base character in the ß-cyclodextrin polyiodide inclusion complex with Co2+ ion: an FT-Raman investigation.

The ß-cyclodextrin (ß-CD) polyiodide inclusion complex (ß-CD)(2)·Co(0.5)·I(7)·21H(2)O has been synthesized, characterized and further investigated via FT-Raman spectroscopy in the temperature range of 30-120°C. The experimental results point to the coexistence of I(-)(7) units (I(2)·I(-)(3)·I(2)) that seem not to interact with the Co(2+) ions and I(-)(7) units that display such interactions. The former units exhibit a disorder-order transition of both their I(2) molecules above 60°C due to a symmetric charge-transfer interaction with the central I(-)(3) [I(2)←I(-)(3)→I(2)], whereas in the latter units only one of the two I(2) molecules becomes well-ordered above 30°C. The other I(2) molecule remains disordered presenting no charge-transfer phenomena. The Co(2+) ion induces a considerable asymmetry on the geometry of the I(-)(3) anion and a significant modification of its Lewis base character. Complementary dielectric measurements suggest no important involvement of H···I contacts in the observed modification of the I(-)(3) electron-transfer properties.

Abolished circadian rhythm of salivary cortisol in elite artistic gymnasts.

OBJECTIVE: The aim of this study was to evaluate the effects of intensive physical exercise and acute psychological stress during high level athletic competition as reflected on the levels of salivary cortisol in elite artistic gymnasts (AGs). DESIGN: The study included 239 AGs (142 females-97 males) who participated in the European Championship of Gymnastics in 2006 and 81 adolescents (40 females-41 males), matched for age, as controls. All athletes participated voluntarily in all or parts of the study, providing samples or data for each of the variables measured. Height, weight, body fat, lean body mass (LBM), bone age and Tanner stage of puberty were assessed and data concerning the time of thelarche, adrenarche and menarche as well as, the onset and the intensity (hours per week) of training were obtained. METHODS: Saliva samples were collected, the morning before training and in the afternoon shortly after the competition. From controls, the saliva samples were collected in the morning. Cortisol concentrations were measured using a chemiluminescence method. Acute stress was assessed using a questionnaire designed for the study. RESULTS: No difference was found between morning and afternoon salivary cortisol levels in both male and female AGs (females: AM: 15.45±7.45nmol/l vs PM: 15.73±9.38nmol/l; males: AM: 10.21±5.52nmol/l vs PM: 9.93±13.8nmol/l, p>0.05). Female AGs presented higher levels of morning salivary cortisol than female controls (p<0.05). Both male and female AGs had higher degree of psychological stress in comparison with controls (p<0.001, p<0.013, respectively). Female AGs had higher morning and afternoon salivary cortisol levels (p<0.01, p<0.01, respectively) and higher degree of stress (p<0.003) than males. CONCLUSIONS: In elite AGs the diurnal rhythm of salivary cortisol has been abolished, probably due to the strenuous training and competition conditions. Female AGs presented higher levels of morning salivary cortisol and psychological stress compared to both male AGs and female controls. The long term consequences of these modifications of the HPA axis remain to be elucidated.

Bone acquisition during adolescence in athletes.

Bone mass (BM) and skeletal size are similar in prepubertal girls and boys and double between the onset of puberty and early adult life. Sex steroids are responsible for the maturation in human skeleton, as well as for the sexual dimorphism, observed after the onset of puberty. Physical activity in childhood is critical for maximizing bone growth and thus for preventing osteoporosis during older age. Therefore, it constitutes the most effective prevention strategy available. In athletes, high-impact loading activities have been shown to improve BM, whereas in sports requiring a lean somatotype (therefore leading to a negative energy balance), the delay in skeletal maturation and pubertal development predisposes athletes to osteopenia and osteoporosis. Although the early onset of training, the continuous intensive exercise and its long duration attenuate bone acquisition, the excess mechanical load to which these athletes are exposed from a young age exerts beneficial effects on bone formation that lead to a positive net-effect on BM.

The influence of intensive physical training on growth and pubertal development in athletes.

Genetic potential for growth can be fully expressed only under favorable environmental conditions. Although moderate physical activity has beneficial effects on growth, excessive physical training may negatively affect it. Sports favoring restricted energy availability, in the presence of high energy expenditure, are of particular concern. In gymnastics, a different pattern in skeletal maturation and linear growth was observed, resulting in an attenuation of growth potential in artistic gymnasts (AG), more pronounced in males than in females. In female rhythmic gymnasts (RG), the genetic predisposition to growth was preserved owing to a late catchup growth phenomenon. In all other sports not requiring strict dietary restrictions, no deterioration of growth has been documented so far. Intensive physical training and negative energy balance alter the hypothalamic pituitary set point at puberty, prolong the prepubertal stage, and delay pubertal development and menarche in a variety of sports. In elite RG and AG, prepubertal stage is prolonged and pubertal development is entirely shifted to a later age, following the bone maturation rather than the chronological age.