In Vivo Predictive Dissolution (IPD) for Carbamazepine Formulations: Additional Evidence Regarding a Biopredictive Dissolution Medium

Novel analytical solutions for convolution in compartmental pharmacokinetic models and application to non-bioequivalent formulations

Deconvolution and convolution are powerful tools that allow decomposition and reconstruction, respectively, of plasma versus time profiles from input and impulse functions. While deconvolution have commonly used compartmental approaches (e.g., Wagner-Nelson or Loo-Riegelman), convolution most typically used the convolution integral which can be solved with numerical methods. In 2005, an analytical solution for one-compartment pharmacokinetic was proposed and has been widely used ever since. However, to the best of our knowledge, analytical solutions for drugs distributed in more than one compartment have not been reported yet. In this paper, analytical solutions for compartmental convolution from both original and exact Loo-Riegelman approaches were developed and evaluated for different scenarios. While convolution from original approach was slightly more precise than that from the exact Loo-Riegelman, both methods were extremely accurate for reconstruction of plasma profiles after respective deconvolutions. Nonetheless, convolution from exact Loo-Riegelman was easier to interpret and to be manipulated mathematically. In fact, convolution solutions for three and more compartments can be easily written with this approach. Finally, our convolution analytical solution was applied to predict the failure in bioequivalence for levonorgestrel, demonstrating that equations in this paper may be useful tools for pharmaceutical scientists.

The quality of drugs and drug products - Always guaranteed?

To ensure the efficacy, safety, and quality of drugs, several national and international guidelines and regulatory requirements exist. The most important international regulatory framework for quality is the collection of the guidelines ICH Q1-Q14 (International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use), which form the basis for the development and approval of medicinal products. Additionally, international and national pharmacopoeias and national regulatory authorities like Food and Drug Administration (FDA) and European Directory for the Quality of Medicines and HealthCare (EDQM) have to be considered during the lifecycle of a drug. Further, regular updates and optimization of processes and methods together with periodic audits and inspections of the manufacturing plants help to ensure compliance with the complex regulatory requirements for medicinal products. Although the pharmaceutical world seems to be very well regulated and controlled, several drug recalls per year have to be announced and conducted to remove defect products from the market and protect the patient from any potential health risk. This review article provides an overview of the most common reasons for such recalls presenting several historical and current cases with a detailed discussion of root causes. A specific focus lies on quality issues like drug degradation, impurity and nitrosamine contamination, lack of drug stability, occurrence and transformation of polymorphs, contamination with particulates and foreign matters, amongst others. The role of APIs, excipients and packaging will be discussed as well as the analytical challenges to detect, control and mitigate such quality issues. A final chapter will discuss the current situation and an outlook on emerging topics and future challenges for drug quality.

Improving Dissolution Behavior and Oral Absorption of Drugs with pH-Dependent Solubility Using pH Modifiers: A Physiologically Realistic Mass Transport Analysis

Orally dosed drugs must dissolve in the gastrointestinal (GI) tract before being absorbed through the epithelial cell membrane. In vivo drug dissolution depends on the GI tract's physiological conditions such as pH, residence time, luminal buffers, intestinal motility, and transit and drug properties under fed and fasting conditions (Paixão, P. et al. Mol. Pharm. 2018 and Bermejo, et al. M. Mol. Pharm. 2018). The dissolution of an ionizable drug may benefit from manipulating in vivo variables such as the environmental pH using pH-modifying agents incorporated into the dosage form. A successful example is the use of such agents for dissolution enhancement of BCS class IIb (high-permeability, low-solubility, and weak base) drugs under high gastric pH due to the disease conditions or by co-administration of acid-reducing agents (i.e., proton pump inhibitors, H2-antagonists, and antacids). This study provides a rational approach for selecting pH modifiers to improve monobasic and dibasic drug compounds' dissolution rate and extent under high-gastric pH dissolution conditions, since the oral absorption of BCS class II drugs can be limited by either the solubility or the dissolution rate depending on the initial dose number. Betaine chloride, fumaric acid, and tartaric acid are examples of promising pH modifiers that can be included in oral dosage forms to enhance the rate and extent of monobasic and dibasic drug formulations. However, selection of a suitable pH modifier is dependent on the drug properties (e.g., solubility and pK_a) and its interplay with the pH modifier pK_a or pK_as. As an example of this complex interaction, for basic drugs with high pK_a and intrinsic solubility values and large doses, a polyprotic pH modifier can be expected to outperform a monoacid pH modifier. We have developed a hierarchical mass transport model to predict drug dissolution of formulations under varying pH conditions including high gastric pH. This model considers the effect of physical and chemical properties of the drug and pH modifiers such as pK_a, solubility, and particle size distribution. This model also considers the impact of physiological conditions such as stomach emptying rate, stomach acid and buffer secretion, residence time in the GI tract, and aqueous luminal volume on drug dissolution. The predictions from this model are directly applicable to in vitro multi-compartment dissolution vessels and are validated by in vitro experiments in the gastrointestinal simulator. This model's predictions can serve as a potential data source to predict plasma concentrations for formulations containing pH modifiers administered under the high-gastric pH conditions. This analysis provides an improved formulation design procedure using pH modifiers by minimizing the experimental iterations under both in vitro and in vivo conditions.

Biowaiver Monograph for Immediate-Release Solid Oral Dosage Forms: Carbamazepine

Literature relevant to assessing whether BCS-based biowaivers can be applied to immediate release (IR) solid oral dosage forms containing carbamazepine as the single active pharmaceutical ingredient are reviewed. Carbamazepine, which is used for the prophylactic therapy of epilepsy, is a non-ionizable drug that cannot be considered "highly soluble" across the range of pH values usually encountered in the upper gastrointestinal tract. Furthermore, evidence in the open literature suggests that carbamazepine is a BCS Class 2 drug. Nevertheless, the oral absolute bioavailability of carbamazepine lies between 70 and 78% and both in vivo and in vitro data support the classification of carbamazepine as a highly permeable drug. Since the therapeutic and toxic plasma level ranges overlap, carbamazepine is considered to have a narrow therapeutic index. For these reasons, a BCS based biowaiver for IR tablets of carbamazepine cannot be recommended. Interestingly, in nine out of ten studies, USP dissolution conditions (900 mL water with 1% SLS, paddle, 75 rpm) appropriately discriminated among bioinequivalent products and this may be a way forward to predicting whether a given formulation will be bioequivalent to the comparator product.

An In Vitro-In Vivo Simulation Approach for the Prediction of Bioequivalence

The aim of this study was to develop a new in vitro–in vivo simulation (IVIVS) approach in order to predict the outcome of a bioequivalence study. The predictability of the IVIVS procedure was evaluated through its application in the development process of a new generic product of amlodipine/irbesartan/hydrochlorothiazide. The developed IVIVS methodology is composed of three parts: (a) mathematical description of in vitro dissolution profiles, (b) mathematical description of in vivo kinetics, and (c) development of joint in vitro–in vivo simulations. The entire programming was done in MATLAB^® and all created scripts were validated through other software. The IVIVS approach can be implemented for any number of subjects, clinical design, variability and can be repeated for thousands of times using Monte Carlo techniques. The probability of success of each scenario is recorded and finally, an overall assessment is made in order to select the most suitable batch. Alternatively, if the IVIVS shows reduced probability of BE success, the R&D department is advised to reformulate the product. In this study, the IVIVS approach predicted successfully the BE outcome of the three drugs. During the development of generics, the IVIVS approach can save time and expenses.

Two-step in vitro-in vivo correlations: Deconvolution and convolution methods, which one gives the best predictability? Comparison with one-step approach

Finding predictive dissolution tests and valid IVIVCs are essential activities in generic industry, as they can be used as substitutes of human bioequivalence studies. IVIVCs can be developed by two different strategies: a one-step approach or a two-step approach. The objectives of this work were to compare different deconvolution and convolution methods used in the development of two-step level A IVIVCs and to study if the relationship between the in vitro dissolution rate and the in vivo dissolution rate should guide the decision between using a two-step approach or a one-step approach during the development of a new IVIVC. When the in vitro and the in vivo dissolution rates had a linear relationship, valid and biopredictive two-step IVIVCs were obtained, although there was not a combination of deconvolution and convolution methods that could be named as the best one, as long as all the prediction errors for any combination were within the limits. It was not possible to obtain a valid two-step IVIVC when the relationship between dissolution rates was non-linear, but the one-step approach was able to overcome this fact and it gave valid IVIVCs regardless of whether the relationship between dissolution rates was linear or non-linear.