Novel pharmacokinetic modelling of transdermal nitroglycerin

Pharmacokinetic Evaluation of Blonanserin Transdermal Patch: Population Analysis and Simulation of Plasma Concentration and Dopamine D2 Receptor Occupancy in Clinical Settings

Blonanserin is an atypical antipsychotic drug with high affinity and selective antagonism for dopamine D₂ and D₃ and serotonin 5-HT_2A receptors. Blonanserin transdermal patch is the first transdermal formulation developed for the treatment of schizophrenia. The purpose of this population pharmacokinetic (PPK) analysis was to evaluate the characteristics of blonanserin pharmacokinetics after transdermal patch application, to estimate the daily fluctuation in blonanserin plasma concentration, and to evaluate the impact of patch application noncompliance to support usage in clinical settings. A total of 3747 plasma blonanserin concentrations from 9 clinical studies (93 healthy volunteers and 348 patients with schizophrenia) were used in the PPK analysis. The plasma concentration was predicted using the final PPK model, and dopamine D₂ receptor occupancy was estimated on the basis of the results of a separately reported positron emission tomography study. A 2-compartment, parallel zero-order absorption with a lag time and first-order elimination model was developed to describe the pharmacokinetics of blonanserin, including the change in absorption rate during patch application. The maximum/minimum ratio of plasma concentration was estimated as 1.10 at steady state, indicating minimal fluctuation. In the case of failure to remove the previous patch or a missing application, the increase or decrease in plasma concentration and dopamine D₂ receptor occupancy was <20%. These results indicated that the plasma blonanserin concentration and dopamine D₂ receptor occupancy were stable after blonanserin transdermal patch application, which may lead to improved tolerability during the treatment of patients with schizophrenia.

Opportunities and Challenges Related to the Implementation of Model-Based Bioequivalence Criteria

The science of bioequivalence and biosimilarity has greatly evolved over the past 3 decades. Current methods for assessing bioequivalence mostly rely on noncompartmental pharmacokinetic (PK) analyses, which have proven to be reliable and robust for most products. However, the development of more complex products is forcing scientists and regulators to consider alternative approaches, including those derived from model-based population PK analyses. This article will examine the strengths and weaknesses of standard noncompartmental methods and compare them to model-based approaches, including a comparison of metrics associated with each method. Specific situations for which model-based approaches could prove to be more suitable will be presented, as well as potential bioequivalence metrics that could be considered for bioequivalence comparisons. The opportunities and challenges that are associated with these novel methods will also be discussed.

Population pharmacokinetic model of transdermal nicotine delivered from a matrix-type patch

AIMS

Nicotine addiction is an issue faced by millions of individuals worldwide. As a result, nicotine replacement therapies, such as transdermal nicotine patches, have become widely distributed and used. While the pharmacokinetics of transdermal nicotine have been extensively described using noncompartmental methods, there are few data available describing the between-subject variability in transdermal nicotine pharmacokinetics. The aim of this investigation was to use population pharmacokinetic techniques to describe this variability, particularly as it pertains to the absorption of nicotine from the transdermal patch.

METHODS

A population pharmacokinetic parent-metabolite model was developed using plasma concentrations from 25 participants treated with transdermal nicotine. Covariates tested in this model included: body weight, body mass index, body surface area (calculated using the Mosteller equation) and sex.

RESULTS

Nicotine pharmacokinetics were best described with a one-compartment model with absorption based on a Weibull distribution and first-order elimination and a single compartment for the major metabolite, cotinine. Body weight was a significant covariate on apparent volume of distribution of nicotine (exponential scaling factor 1.42). After the inclusion of body weight in the model, no other covariates were significant.

CONCLUSIONS

This is the first population pharmacokinetic model to describe the absorption and disposition of transdermal nicotine and its metabolism to cotinine and the pharmacokinetic variability between individuals who were administered the patch.

Interindividual variation in transdermal and oral drug deliveries

It is generally assumed that the topical absorption of drugs is subject to more interindividual variation than the oral absorption of drugs. To date, we are unaware of any clinical studies or meta-analyses that compare the interindividual variation of transdermal and oral drug deliveries for a large number of medications. In this research article, the absorption data for 10 medications that can be used as an oral medication or a transdermal patch were compiled, and from the collected data, the interindividual variance was calculated for topical and oral absorption as an overall average and by drug. This research article also briefly reviews the pharmacokinetics and pharmacodynamics of transdermal and oral drug absorption. Our results indicate that there is considerable interindividual variation in topical and oral absorption for the 10 medications investigated. Yet, surprisingly, the calculated overall mean and median coefficient of variation (CV) for topical and oral absorption were comparable (within 10% of each other). Therefore, the interindividual variation in topical and oral absorption may not be as divergent as assumed previously. In a drug-by-drug comparison, certain medications demonstrated considerably more variation when absorbed orally versus topically and vice versa. It is unclear why certain drugs had less variation in absorption when delivered topically versus orally (or vice versa). However, patterns in drug molecular weight (MW) or octanol partition coefficient (log K(OCT) ) could not totally explain these findings. In our analysis, the previously reported correlation between MW or log K(OCT) and interindividual variation in absorption could only be replicated when plotting the topical absorption CV and MW. What became clear from our analysis is that the drug itself is an important variable when considering which route of delivery (oral or topical) will provide the least amount of interindividual variation. Our study had many limitations because of study design, which may have affected our calculations and conclusions. Further experimentation is needed to support and reveal the basic science of skin or drug chemistry that can further explain these findings.

A theoretical model for transdermal drug delivery from emulsions and its dependence upon formulation

This article presents a theoretical model of transdermal drug delivery from an emulsion-type vehicle that addresses the vehicle heterogeneity and incorporates the prediction of drug transport parameters as function of the vehicle composition. The basic mass transfer model considers interfacial and diffusion resistances within the emulsion and partition/diffusion phenomena across two skin compartments in series. Drug transport parameters are predicted as follows: partition coefficients are derived from regular solutions theory, drug diffusivity in the continuous phase is computed from a free volume theory with segmental motion, and permeability of the surfactant layer around droplets is estimated based on a free surface area model. These relationships are incorporated within the basic mass transfer model, so that the overall model is able to predict temporal profiles of drug release from the vehicle and of drug concentration in plasma, as a function of vehicle composition. In this way, the proposed model provides a sound physicochemical basis to support the development of new formulations and the planning of experiments. A simulated case study regarding a nitroglycerin ointment is presented in detail, illustrating how thermodynamic and kinetic factors inherent to the emulsion vehicle can modulate drug release and subsequent systemic absorption.

Transdermal drug pharmacokinetics in man: Interindividual variability and partial prediction

A database of human dermatopharmacokinetic parameters of 12 transdermal patches is established. The effect of system design, application site, and metabolism on pharmacokinetic data is discussed, and interindividual variability of data and its possible sources evaluated. Using multiple regression analysis, two equations based on drugs physicochemical characteristics are suggested for partial prediction of peak plasma concentration (C(max)) after patch application. Patch application presumably decreases variance as rub-off, wash and exfoliation steps are diminished. The results showed that interindividual variation, in terms of coefficient of variation (CV) of C(max), is inversely correlated with drugs molecular weight and lipophilicity in the range of 200<MW<400 and 1.6<logK(oct)<4.3. Multiple regression analysis of C(max) against physichochemical parameters demonstrated the prominent contribution of hydrogen bonding acceptability of the molecules on their maximal plasma concentration after patch administration. The findings suggest that the serum concentration profile for transdermal therapeutic systems (TTS) is a net result of the system performance, drug absorption and elimination. Thus, the variability in serum concentration is a function of variability of each process involved. This should be noted in explanation of effect of molecular features of drugs on their plasma concentration profile.

Clinical pharmacokinetics and pharmacodynamics of glyceryl trinitrate and its metabolites

This review discusses the pharmacokinetics and pharmacodynamics of glyceryl trinitrate (nitroglycerin; GTN) pertinent to clinical medicine. The pharmacokinetics of GTN associated with various dose regimens are characterised by prominent intra- and inter-individual variability. It is, nevertheless, important to clearly understand the pharmacokinetics and characteristics of GTN to optimise its use in clinical practice and, in particular, to obviate the development of tolerance. Measurements of plasma concentrations of GTN and of 1,2-glyceryl dinitrate (1,2-GDN), 1,3-glyceryl dinitrate (1,3-GDN), 1-glyceryl mononitrate (1-GMN), and 2-glyceryl mononitrate (2-GMN), its four main metabolites, remain difficult and require meticulous techniques to obtain reliable results. Since GDNs have an effect on haemodynamic function, pharmacokinetic analyses that include the parent drug as well as the metabolites are important. Although the precise mechanisms of GTN metabolism have not been elucidated, two main pathways have been proposed for its biotransformation. The first is a mechanism-based biotransformation pathway that produces nitric oxide (NO) and contributes directly to vasodilation. The second is a clearance-based biotransformation or detoxification pathway that produces inorganic nitrite anions (NO(2) -). NO(2) - has no apparent cardiovascular effect and is not converted to NO in pharmacologically relevant concentrations in vivo. In addition, several non-enzymatic and enzymatic systems are capable of metabolising GTN. This complex metabolism complicates considerably the evaluation of the pharmacokinetics and pharmacodynamics of GTN. Regardless of the route of administration, concentrations of the metabolites exceed those of the parent compound by several orders of magnitude. During continuous steady-state delivery of GTN, for instance by a patch, concentrations of 1,2-GDN are consistently 2-7 times higher than those of 1,3-GDN, and concentrations of 2-GMN are 4-8 times higher than those of 1-GMN. Concentrations of GDNs are approximately 10 times higher, and of GMNs approximately 100 times higher, than those of GTN during sustained administration. The development of tolerance is closely related to the metabolism of GTN, and can be broadly categorised as haemodynamic tolerance versus vascular tolerance. Efforts are warranted to circumvent the development of tolerance and facilitate the use of GTN in clinical practice. Although this remains to be accomplished, it is likely that, in the near future, regimens will be developed based on a full understanding of the pharmacokinetics and pharmacodynamics of GTN and its metabolites.

Population pharmacokinetics of nitroglycerin and of its two metabolites after a single 24-hour application of a nitroglycerin transdermal matrix delivery system

The purpose of this study was to assess the ability of our previously constructed pharmacokinetic (PK) model to describe nitroglycerin (GTN), 1,2-dinitroglycerin (1,2-GDN), and 1,3-dinitroglycerin (1,3-GDN) plasma concentrations after a single-dose application of a GTN transdermal matrix delivery system. GTN, 1,2-GDN, and 1,3-GDN plasma concentrations were simultaneously fitted using a first-pass, mixed-order release, one-compartment PK model. Population PK parameter values were derived using an iterative two-stage methodology (IT2S). Some of the mean PK parameters estimates and their interindividual variability (CV%) were the percentage of the delivered GTN dose reaching the systemic circulation released by a first-order process A, 53% (44); the 1,2-GDN and 1,3-GDN formation rate constants, k(f1)9 h(-1) (67) and k(f2) 0.5 h(-1) (38), respectively; the metabolite elimination rate constant, k(m) 1 h(-1) (27); GTN, 1,2-GDN, and 1,3-GDN volumes of distribution (Vc/F 6 L [45]), V2/F 78 L [51]), and V3/F 29 L [40]), respectively). Mean calculated elimination half-lives (t1/2+/-standard deviation [SD]) for GTN and the GDN metabolites were 7+/-4 minutes and 33+/-7 minutes, respectively. The proposed PK model fitted the observed plasma concentrations of GTN, 1,2-GDN, and 1,3-GDN very well. This new transdermal matrix delivery system appears to behave pharmacokinetically in the same manner as a transdermal reservoir delivery system (Transderm-Nitro, Ciba-Geigy, Mississauga, Canada).