The bioinequivalence of carbamazepine tablets with a history of clinical failures

An Evaluation of Wet Granulation Process Selection for API Prone to Polymorphic Form Conversion in the Presence of Moisture and Heat

PURPOSE

Wet granulation (WG) is one of the most versatile processes to improve blend properties for processing. However, due to its need for moisture and heat, it is often considered not amenable to active pharmaceutical ingredients (APIs) prone to forming hydrates. Despite this claim, little literature exists evaluating the extent to which polymorphic form conversions occur for such API when processed with WG. This work sets out to explore two common WG methods, high-shear (HSG) and fluid-bed (FBG), and two drying processes, tray-drying (TD) and fluid-bed drying (FBD), and evaluate the risk they pose to hydrate form conversion.

METHODS

The progression of anhydrous to hydrate form conversion of two model compounds with vastly different solubilities, fexofenadine hydrochloride and carbamazepine, was monitored throughout the various processes using powder X-ray diffraction. The resultant granules were characterized using thermogravimetric analysis, differential scanning calorimetry, BET adsorption, and sieve analysis.

RESULTS

FBG and FBD processing resulted in the preservation of the original form of both APIs, while HSG+TD resulted in the complete conversion of the API. The FBD of fexofenadine and carbamazepine granules prepared with HSG resulted in partial and complete re-conversion back to the original anhydrous forms, respectively.

CONCLUSION

The drying process is a critical factor in anhydrous form conservation. FBG and FBD yielded better preservation of the initial anhydrous forms. HSG could be an acceptable granulation method for API susceptible to hydrate formation if the API solubility is low. Selecting an FBG+FBD process minimizes API hydrate formation and preserves the original anhydrous form.

Insightful vibrational imaging study on the hydration mechanism of carbamazepine

Anhydrous carbamazepine (CBZ) is an anti-convulsant drug commonly used to treat epilepsy and relieve trigeminal neuralgia. The presence of the dihydrate form in commercial CBZ tablets can change the dissolution rate of the active pharmaceutical ingredient (API), thus decreasing its activity. The hydration transformation can occur during wet granulation or storage, within a few weeks, depending on the ambient conditions. This work aims to investigate the effect of relative humidity (RH) in the transition of pure anhydrous CBZ (CBZ III) into the hydrate form by using confocal Raman microscopy with cluster analysis (CA). Firstly, several tablets of pure CBZ III containing different amounts of CBZ DH (50%, 10%, 1%, 0.5%) were prepared and analyzed by Raman imaging with CA. Our results show that CBZ DH crystals can be detected in the CBZ III tablets, at as low a concentration as 0.5%, giving distinct Raman features for the analysed polymorphs. The stability of pure anhydrous (CBZ III) tablets was then monitored by Raman imaging at room temperature (20-22 °C) and different RH (6%, 60% and 89%). The Raman imaging with CA showed that the anhydrous CBZ tablets start to convert into the hydrate form after 48 h, and it completely changes after 120 hours (5 days) at RH 89%. The tablets exposed to RH 6% and 60% did not demonstrate the presence of CBZ DH after 1 week of exposure. The exposure time was extended for 9 months in the former, and no CBZ DH was observed. A comparative study using IR imaging was also performed, demonstrating the viability of these vibrational imaging techniques as valuable tools to monitor the hydration process of active pharmaceutical ingredients.

Therapeutic Basis of Generic Substitution of Antiseizure Medications

More than thirty antiseizure medications (ASMs) are available for treating epilepsy. ASMs differ in their potency and efficacy in controlling seizures by acting on diverse targets in the brain, often with variable pharmacokinetics. Moreover, nearly 30% of people with epilepsy have drug-resistant or intractable seizures. Generic substitution of ASMs is a complex issue. It is thought that frequent generic substitution in people with epilepsy may cause problems because the U.S. Food and Drug Administration (FDA) rules allow too much variability across products. The standard bioequivalence range (80% to 125%) appears too broad for many ASMs, especially those exhibiting little separation between therapeutic and toxic levels. Hence, sub-therapeutic concentration may lead to therapeutic failure with seizure recurrence, which could be life threatening. A supra-therapeutic level could result in adverse effects or compliance issues. There are reported issues with generic substitutions of phenytoin, topiramate, levetiracetam, carbamazepine, and lamotrigine. There is discussion in the epilepsy community about additional guidelines, including designation of generic ASMs as Narrow Therapeutic Index (NTI) drugs and how patient education plays a role in generic substitution. Overall, based on the published evidence on specific generic ASMs, FDA bioequivalence standards are not the cause of problems with generic ASM substitution. Rather, it is imperative that physicians and pharmacists provide adequate patient education on what to expect when switching to generic ASMs, including changes in medication shape and color. Another suggestion would be to consider that all ASMs be considered for inclusion in NTI class to prevent the clinical outcome issues associated with generic ASM switching. SIGNIFICANCE STATEMENT: There are critical aspects to consider when switching from a brand name antiseizure medication (ASM) when a generic becomes available or switching between generics. Generic ASMs are interchanged with little consideration of differences in therapeutic equivalence and other clinical factors. This article describes key issues on generic substitution of ASMs and highlights critical pharmacotherapeutic issues associated with generic ASMs.

Carbamazepine polymorphism: a re-visitation using Raman imaging

Raman imaging methods have appeared in the last years as a powerful approach to monitoring the quality of pharmaceutical compounds. Because polymorphism occurs in many crystalline pharmaceutical compounds, it is essential to monitor polymorphic transformations induced by different external stimulus, such as temperature changes, to which those compounds may be submitted. Raman imaging with k-means cluster analysis (CA) is used here as an essential technique to investigate structural and chemical transformations occurring in carbamazepine p-monoclinic (CBZ III) into carbamazepine triclinic (CBZ I) when submitted to temperatures near the melting point of CBZ III (178 °C) and CBZ I (193°C). CBZ III commercial powder and laboratorial prepared CBZ I were analyzed by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy with variable temperature. After thermal treatment, the resultant CBZ powder was evaluated by Raman imaging, in which all imaging data was analyzed using CA. Raman imaging allowed the identification of different polymorphs of CBZ (CBZ III and CBZ I) and iminostilbene (IMS), a degradation product of CBZ, in the treated samples, depending on the heating treatment method.

Understanding stress-induced disorder and breakage in organic crystals: beyond crystal structure anisotropy

Crystal engineering has advanced the strategies for design and synthesis of organic solids with the main focus being on customising the properties of the materials. Research in this area has a significant impact on large-scale manufacturing, as industrial processes may lead to the deterioration of such properties due to stress-induced transformations and breakage. In this work, we investigate the mechanical properties of structurally related labile multicomponent solids of carbamazepine (CBZ), namely the dihydrate (CBZ·2H2O), a cocrystal of CBZ with 1,4-benzoquinone (2CBZ·BZQ) and the solvates with formamide and 1,4-dioxane (CBZ·FORM and 2CBZ·DIOX, respectively). The effect of factors that are external (e.g. impact stressing) and/or internal (e.g. phase transformations and thermal motion) to the crystals are evaluated. In comparison to the other CBZ multicomponent crystal forms, CBZ·2H2O crystals tolerate less stress and are more susceptible to breakage. It is shown that this poor resistance to fracture may be a consequence of the packing of CBZ molecules and the orientation of the principal molecular axes in the structure relative to the cleavage plane. It is concluded, however, that the CBZ lattice alone is not accountable for the formation of cracks in the crystals of CBZ·2H2O. The strength and the temperature-dependence of electrostatic interactions, such as hydrogen bonds between CBZ and coformer, appear to influence the levels of stress to which the crystals are subjected that lead to fracture. Our findings show that the appropriate selection of coformer in multicomponent crystal forms, targetting superior mechanical properties, needs to account for the intrinsic stress generated by molecular vibrations and not solely by crystal anisotropy. Structural defects within the crystal lattice, although highly influenced by the crystallisation conditions and which are especially difficult to control in organic solids, may also affect breakage.

Development of a Pediatric Relative Bioavailability/Bioequivalence Database and Identification of Putative Risk Factors Associated With Evaluation of Pediatric Oral Products

Generally, bioequivalence (BE) studies of drug products for pediatric patients are conducted in adults due to ethical reasons. Given the lack of direct BE assessment in pediatric populations, the aim of this work is to develop a database of BE and relative bioavailability (relative BA) studies conducted in pediatric populations and to enable the identification of risk factors associated with certain drug substances or products that may lead to failed BE or different pharmacokinetic (PK) parameters in relative BA studies in pediatrics. A literature search from 1965 to 2020 was conducted in PubMed, Cochrane Library, and Google Scholar to identify BE studies conducted in pediatric populations and relative BA studies conducted in pediatric populations. Overall, 79 studies covering 37 active pharmaceutical ingredients (APIs) were included in the database: 4 bioequivalence studies with data that passed BE evaluations; 2 studies showed bioinequivalence results; 34 relative BA studies showing comparable PK parameters, and 39 relative BA studies showing differences in PK parameters between test and reference products. Based on the above studies, common putative risk factors associated with differences in relative bioavailability (DRBA) in pediatric populations include age-related absorption effects, high inter-individual variability, and poor study design. A database containing 79 clinical studies on BE or relative BA in pediatrics has been developed. Putative risk factors associated with DRBA in pediatric populations are summarized.

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.

Study of In Vitro and In Vivo Carbamazepine Release from Coarse and Nanometric Pharmaceutical Emulsions Obtained via Ultra-High-Pressure Homogenization

In the past decade, pharmaceutical nanotechnology has proven to be a promising alternative for improving the physicochemical and biopharmaceutical features for conventional pharmaceutical drug formulations. The goal of this study was to develop, characterize, and evaluate the in vitro and in vivo release of the model drug carbamazepine (CBZ) from two emulsified formulations with different droplet sizes (coarse and nanometric). Briefly, oil-in-water emulsions were developed using (i) Sacha inchi oil, ultrapure water, TweenTM 80, and SpanTM 80 as surfactants, (ii) methyl-paraben and propyl-paraben as preservatives, and (iii) CBZ as a nonpolar model drug. The coarse and nanometric emulsions were prepared by rotor-stator dispersion and ultra-high-pressure homogenization (UHPH), respectively. The in vitro drug release studies were conducted by dialysis, whereas the in vivo drug release was evaluated in New Zealand breed rabbits. The results showed that nanoemulsions were physically more stable than coarse emulsions, and that CBZ had a very low release for in vitro determination (<2%), and a release of 20% in the in vivo study. However, it was found that nanoemulsions could significantly increase drug absorption time from 12 h to 45 min.

Applications of Powder X-Ray Diffraction in Small Molecule Pharmaceuticals: Achievements and Aspirations

Since the discovery of X-ray diffraction and its potential to elucidate crystal symmetry, powder X-ray diffraction has found diverse applications in the field of pharmaceutical sciences. This review summarizes significant achievements of the technique during various stages of dosage form development. Improved understanding of the principle involved and development of automated hardware and reliable software have led to increased instrumental sensitivity and improved data analysis. These advances continue to expand the applications of powder X-ray diffraction to emerging research fields such as amorphous systems, mechanistic understanding of phase transformations, and "Quality by Design" in formulation development.

Influences of Crystal Anisotropy in Pharmaceutical Process Development

Crystalline materials are of crucial importance to the pharmaceutical industry, as a large number of APIs are formulated in crystalline form, occasionally in the presence of crystalline excipients. Owing to their multifaceted character, crystals were found to have strongly anisotropic properties. In fact, anisotropic properties were found to be quite important for a number of processes including milling, granulation and tableting. An understanding of crystal anisotropy and an ability to control and predict crystal anisotropy are mostly subjects of interest for researchers. A number of studies dealing with the aforementioned phenomena are grounded on over-simplistic assumptions, neglecting key attributes of crystalline materials, most importantly the anisotropic nature of a number of their properties. Moreover, concepts such as the influence of interfacial phenomena in the behaviour of crystalline materials during their growth and in vivo, are still poorly understood. The review aims to address concepts from a molecular perspective, focusing on crystal growth and dissolution. It begins with a brief outline of fundamental concepts of intermolecular and interfacial phenomena. The second part discusses their relevance to the field of pharmaceutical crystal growth and dissolution. Particular emphasis is given to works dealing with mechanistic understandings of the influence of solvents and additives on crystal habit. Furthermore, comments and perspectives, highlighting future directions for the implementation of fundamental concepts of interfacial phenomena in the rational understanding of crystal growth and dissolution processes, have been provided.

Investigation of the Sensitivity of Transmission Raman Spectroscopy for Polymorph Detection in Pharmaceutical Tablets

Polymorph detection is critical for ensuring pharmaceutical product quality in drug substances exhibiting polymorphism. Conventional analytical techniques such as X-ray powder diffraction and solid-state nuclear magnetic resonance are utilized primarily for characterizing the presence and identity of specific polymorphs in a sample. These techniques have encountered challenges in analyzing the constitution of polymorphs in the presence of other components commonly found in pharmaceutical dosage forms. Laborious sample preparation procedures are usually required to achieve satisfactory data interpretability. There is a need for alternative techniques capable of probing pharmaceutical dosage forms rapidly and nondestructively, which is dictated by the practical requirements of applications such as quality monitoring on production lines or when quantifying product shelf lifetime. The sensitivity of transmission Raman spectroscopy for detecting polymorphs in final tablet cores was investigated in this work. Carbamazepine was chosen as a model drug, polymorph form III is the commercial form, whereas form I is an undesired polymorph that requires effective detection. The concentration of form I in a direct compression tablet formulation containing 20% w/w of carbamazepine, 74.00% w/w of fillers (mannitol and microcrystalline cellulose), and 6% w/w of croscarmellose sodium, silicon dioxide, and magnesium stearate was estimated using transmission Raman spectroscopy. Quantitative models were generated and optimized using multivariate regression and data preprocessing. Prediction uncertainty was estimated for each validation sample by accounting for all the main variables contributing to the prediction. Multivariate detection limits were calculated based on statistical hypothesis testing. The transmission Raman spectroscopic model had an absolute prediction error of 0.241% w/w for the independent validation set. The method detection limit was estimated at 1.31% w/w. The results demonstrated that transmission Raman spectroscopy is a sensitive tool for polymorphs detection in pharmaceutical tablets.

Clinical implications for substandard, nonproprietary medicines in multiple sclerosis: focus on fingolimod

Both proprietary and nonproprietary medicines are expected to undergo rigorous preapproval testing and both should meet stringent health authority regulatory requirements related to quality to obtain approval. Nonproprietary (also known as copy, or generic) medicines, which base their authorization and use on the proprietary documentation and label, are often viewed as a means to help lower the cost and, thus, increase patient access. If these medicines fail to meet quality standards, such as good manufacturing practice and bioequivalence (in humans), they are then defined as substandard copies and can pose serious risks to patients in terms of safety and efficacy. Potentially noncontrolled or different manufacturing process and excipients in nonproprietary medicines may result in poor batch-to-batch reproducibility (accurate and consistent quantity of each ingredient in each capsule/tablet) and lower quality. Substandard, nonproprietary copies of medicines that are immunomodulatory or immunosuppressive are of concern to patients due to their possible untoward safety and lack of efficacy events. This article reviews the potential risks associated with nonproprietary medicines that do not meet the regulatory requirements of the United States Food and Drug Administration, the European Medicines Agency, or the World Health Organization. The clinical implications for patients are described. This article focuses on nonproprietary medicines for multiple sclerosis, particularly fingolimod, that are not identical to proprietary versions and could thus fail to meet efficacy expectations or have different impact on the safety of patients with multiple sclerosis.

Potential problems and recommendations regarding substitution of generic antiepileptic drugs: a systematic review of literature

Despite the availability of generic antiepileptic drugs (AEDs), still patients and neurologists hesitate to make a switch due to assorted reasons. The objectives of this review were to evaluate the risks associated with the generic substitution of AEDs. In this context, we also summarized the recommendations of various international societies to treat epileptic patients. We used a number of electronic databases to identify the relevant published studies which demonstrated the potential problems and recommendations regarding generic substitution of AEDs. Of 204 articles found initially, 153 were selected for additional review. Subsequently, 68 articles were finally selected. This review concluded that potential problems linked with the generic substitution of AEDs could be bioequivalence issues, failure of drug therapy, emergence of adverse events and increase in the frequency of seizures. The reasons could be the pharmacokinetics properties of AEDs and unique characteristics of some epilepsy patients. Consequently, the generic substitution of AEDs affects the successful treatment and quality of life of the patients. Various guidelines recommend the well-controlled epileptic patients to avoid switching from brand-to-generic products, generic-to-brand products or generic to some other generic products.

Polymorph Impact on the Bioavailability and Stability of Poorly Soluble Drugs

Drugs with low water solubility are predisposed to poor and variable oral bioavailability and, therefore, to variability in clinical response, that might be overcome through an appropriate formulation of the drug. Polymorphs (anhydrous and solvate/hydrate forms) may resolve these bioavailability problems, but they can be a challenge to ensure physicochemical stability for the entire shelf life of the drug product. Since clinical failures of polymorph drugs have not been uncommon, and some of them have been entirely unexpected, the Food and Drug Administration (FDA) and the International Conference on Harmonization (ICH) has required preliminary and exhaustive screening studies to identify and characterize all the polymorph crystal forms for each drug. In the past, the polymorphism of many drugs was detected fortuitously or through manual time consuming methods; today, drug crystal engineering, in particular, combinatorial chemistry and high-throughput screening, makes it possible to easily and exhaustively identify stable polymorphic and/or hydrate/dehydrate forms of poorly soluble drugs, in order to overcome bioavailability related problems or clinical failures. This review describes the concepts involved, provides examples of drugs characterized by poor solubility for which polymorphism has proven important, outlines the state-of-the-art technologies and discusses the pertinent regulations.

The development of carbamazepine-succinic acid cocrystal tablet formulations with improved in vitro and in vivo performance

The use of soluble cocrystal for delivering drugs with low solubility, although a potentially effective approach, often suffers the problem of rapid disproportionation during dissolution, which negates the solubility advantages offered by the cocrystal. This necessitates their robust stabilization in order for successful use in a tablet dosage form. The cocrystal between carbamezepine and succinic acid (CBZ-SUC) exhibits a higher aqueous solubility than its dihydrate, which is the stable form of CBZ in water. Using this model system, we demonstrate an efficient and material-sparing tablet formulation screening approach enabled by intrinsic dissolution rate measurements. Three tablet formulations capable of stabilizing the cocrystal both under accelerated condition of 40 °C and 75% RH and during dissolution were developed using three different polymers, Soluplus® (F1), Kollidon VA/64 (F2) and Hydroxypropyl methyl cellulose acetate succinate (F3). When compared to a marketed product, Epitol® 200 mg tablets (F0), drug release after 60 min from formulations F1 (∼82%), F2 (∼95%) and F3 (∼95%) was all higher than that from Epitol® (79%) in a modified simulated intestinal fluid. Studies in albino rabbits show correspondingly better bioavailability of F1-F3 than Epitol.

Raman spectroscopy in pharmaceutical product design

Almost 100 years after the discovery of the Raman scattering phenomenon, related analytical techniques have emerged as important tools in biomedical sciences. Raman spectroscopy and microscopy are frontier, non-invasive analytical techniques amenable for diverse biomedical areas, ranging from molecular-based drug discovery, design of innovative drug delivery systems and quality control of finished products. This review presents concise accounts of various conventional and emerging Raman instrumentations including associated hyphenated tools of pharmaceutical interest. Moreover, relevant application cases of Raman spectroscopy in early and late phase pharmaceutical development, process analysis and micro-structural analysis of drug delivery systems are introduced. Finally, potential areas of future advancement and application of Raman spectroscopic techniques are discussed.

Polymorphism: an evaluation of the potential risk to the quality of drug products from the Farmácia Popular Rede Própria

Polymorphism in solids is a common phenomenon in drugs, which can lead to compromised quality due to changes in their physicochemical properties, particularly solubility, and, therefore, reduce bioavailability. Herein, a bibliographic survey was performed based on key issues and studies related to polymorphism in active pharmaceutical ingredient (APIs) present in medications from the Farmácia Popular Rede Própria. Polymorphism must be controlled to prevent possible ineffective therapy and/or improper dosage. Few mandatory tests for the identification and control of polymorphism in medications are currently available, which can result in serious public health concerns.

Influence of sodium lauryl sulfate and tween 80 on carbamazepine-nicotinamide cocrystal solubility and dissolution behaviour

The influence of the surfactants of sodium lauryl sulfate (SLS) and Tween 80 on carbamazepine–nicotinamide (CBZ–NIC) cocrystal solubility and dissolution behaviour has been studied in this work. The solubility of the CBZ–NIC cocrystal was determined by measuring the eutectic concentrations of the drug and the coformer. Evolution of the intrinsic dissolution rate (IDR) of the CBZ–NIC cocrystal was monitored by the UV imaging dissolution system during dissolution. Experimental results indicated that SLS and Tween 80 had little influence upon the solubility of the CBZ–NIC cocrystal but they had totally opposite effects on the IDR of the CBZ–NIC cocrystal during dissolution. SLS significantly increased the IDR of the CBZ–NIC cocrystal while Tween 80 decreased its IDR.

Comparative in vitro dissolution study of carbamazepine immediate-release products using the USP paddles method and the flow-through cell system

Dissolution profiles of four carbamazepine immediate-release generic products (200 mg tablets) and the reference product Tegretol® were evaluated using the USP paddles method and an alternative method with the flow-through cell system, USP Apparatus 4. Under official conditions all products met the Q specification, dissolution profiles of generic products were similar to the dissolution profile of the reference product (f 2 > 50) and model-independent parameters showed non significant differences to the reference product except mean dissolution time for product A (p < 0.05). On the other hand, when the flow-through cell system was used, none of the products met the pharmacopeial specification at 15 min and product A did not reach dissolution criteria at 60 min, dissolution profiles of all generic products were not similar to the reference product profile (f 2 < 50) and all model-independent parameters showed significant differences compared to the reference product (p < 0.05). Weibull's model was more useful for adjusting the dissolution data of all products in both USP apparatuses and Td values showed significant differences compared to the reference product (p < 0.05) when USP Apparatus 4 was used. These results indicate that the proposed method, using the flow-through cell system, is more discriminative in evaluating both, rate and extent of carbamazepine dissolution process from immediate-release generic products.

Bioequivalence and Bioavailability Clinical Trials: A Status Report from the National Institutes of Health ClinicalTrials.gov Registry

Drug development is an expensive process that is marked by a high-failure rate. For this reason early stage bioequivalence and pharmacokinetic studies are essential in determining the fate of new drug products. In this study, we sought to systematically assess the current trends of ongoing and recently completed bioequivalence and bioavailability trials that have been registered within a national clinical trials registry. All bioequivalence and bioavailability studies registered in the United States ClinicalTrials.gov registry from late-2007 through 2011 were identified. Over this period, more than 2300 interventional bioequivalence and bioavailability trials were registered. As of 2013, the vast majority of studies (86%) have been completed, 10% are actively recruiting participants, and the remainder are engaged in data analysis (4%). When compared to completed trials, ongoing trials are in later phases of clinical development, recruiting larger numbers of participants, and more likely to recruit women and children (P<0.001 for all). These data suggest that the quality of bioequivalence and bioavailability studies has improved rapidly, even over the last five years. However, further work is needed to sustain – and accelerate – these improvements in the design of bioequivalence and bioavailability studies to ensure that safe and efficacious medicines swiftly reach healthcare providers and their patients.

In situ monitoring of carbamazepine-nicotinamide cocrystal intrinsic dissolution behaviour

Cocrystals have shown huge potential to improve the dissolution rate and absorption of a poorly water soluble drug. However, solution mediated phase transformation of cocrystals could greatly reduce the enhancement of its apparent solubility and dissolution rate. The aim of this study is to gain a deep understanding of the phase transition behaviour of cocrystals during dissolution and to investigate the improvement of dissolution rate. Dissolution and transformation behaviour of carbamazepine-nicotinamide (CBZ-NIC) cocrystal, physical mixture and different forms of carbamazepine: form I (CBZ I), form III (CBZ III) and dihydrate (CBZ DH) were studied by different in situ techniques of UV imaging and Raman spectroscopy. It has been found that compared with CBZ III and I, the rate of intrinsic dissolution rate (IDR) of CBZ-NIC cocrystal decreases slowly during dissolution, indicating the rate of crystallisation of CBZ DH from the solution is slow. In situ solid-state characterisation has shown the evolution of conversion of CBZ-NIC cocrystal and polymorphs to its dihydrate form. The study has shown that in situ UV imaging and Raman spectroscopy with a complementary technique of SEM can provide an in depth understanding during dissolution of cocrystals.

Recrystallization of commercial carbamazepine samples-a strategy to control dissolution variability

Physical properties of commercial carbamazepine (CBZ) samples can significantly influence drug release and thereby jeopardize bioequivalence of the final dosage form. The aim of this study was to reduce variability in commercial CBZ samples by recrystallization. CBZ samples of four different suppliers were recrystallized in ethanol solution containing 1% polyvinylpyrrolidone (PVP). CBZ samples were analyzed by disk intrinsic dissolution rate (DIDR), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Recrystallized CBZ samples showed strongly reduced variability in DIDR compared to the untreated CBZ samples. Moreover, transformation process to CBZ dihydrate was inhibited; no dihydrate crystals were visible on compact surfaces after 8 h intrinsic dissolution measurement. Recrystallized CBZ samples showed no change in polymorphic form, however, particle size and shape was inhomogenous. In binary mixtures with microcrystalline cellulose, recrystallized CBZ samples again showed difference in drug release. This difference was associated with the inhomogenous particle size in the recrystallized CBZ samples. The results show that a controlled grinding step is required after recrystallization. We suggest the recrystallization in presence of 1% PVP followed by a controlled grinding step as a strategy to reduce dissolution variability in commercial CBZ samples.

Solution-mediated phase transformation: significance during dissolution and implications for bioavailability

Solubility improvement of poorly soluble drug compounds is a key approach to ensuring the successful development of many new drugs. Methods used to improve the solubility of drug compounds include forming a salt, cocrystal, or amorphous solid. These methods of improving solubility can often lead to a phenomenon called solution-mediated phase transformation, a phase change that is facilitated through exposure to solution. Solution-mediated phase transformation occurs in three steps: dissolution to create a supersaturated solution followed by nucleation of less soluble phase and the growth of that phase. When the growth of the less soluble phase occurs on the surface of the metastable solid, this phenomenon can cause a marked decrease in dissolution rate during in vitro dissolution evaluation, and ultimately in vivo. Therefore, transformation to a less soluble solid during dissolution is an important aspect to consider when evaluating approaches to increase the solubility of a poorly soluble drug. Identification of solution-mediated phase transformation during dissolution is reviewed for powder dissolution, rotating disk method, and channel flow-through apparatus. Types of solution-mediated phase transformation are described in this report, including those involving salts, polymorphs, amorphous solids, and cocrystals. Many experimental examples are provided. Evidence of potential solution-mediated phase transformation in vivo is discussed to better understand the relationship between in vitro dissolution evaluation and in vivo performance.

Carbamazepine-loaded porous microspheres for short-term sustained drug delivery

The present investigation is aimed to prepare the porous microspheres of carbamazepine using eudragit as release retardant, compritol as core forming agent, and HPMC as re-crystallization inhibitor for short-term sustained delivery of carbamazepine. The proposed microspheres were formulated using the emulsion solvent diffusion method. The obtained microspheres were characterized for its particle size distribution, thermal analysis (DSC), crystallinity (PXRD), surface morphology (SEM), and in vitro drug release. The prepared microspheres were found to be optimal in terms of particle size and entrapment efficacy. However, the obtained entrapment efficacy is insufficient to deliver the high dose drug such as carbamazepine. There were no compatibility issues and the drug is partially present in crystalline form in microspheres, which were confirmed by DSC and PXRD, respectively. The time to release 50% of drug from microspheres were in the range of 0.5 - 3.0 h, which could be used to prevent the formation of dihydrate and high extent of drug release. Further investigations are required to reduce the amount of polymer in microspheres that can provide maximum drug loading and acceptable dosage form.