Relationship between rheological properties, in vitro release and in vivo equivalency of topical formulations of diclofenac

Topical drug delivery by Sepineo P600 emulgel: Relationship between rheology, physical stability, and formulation performance

The objective of this present work was to develop and optimize oil-in-water (O/W) emulsion-based gels, namely emulgels that allow maximum topical drug delivery while having desired microstructure and acceptable physical stability. Emulgels containing 2.0 wt% lidocaine were prepared using various concentrations (0.75-5.0 wt%) of Sepineo P600. Their droplet size distribution, physical stability, rheological behaviors, in vitro drug release, and skin permeation profiles were evaluated. Results show that the concentration of Sepineo P600 significantly influenced the microstructure, rheology, and physical stability of the emulgel formulations. The physico-chemical properties also reveals that at least 1.0 wt% Sepineo P600 was needed to produce stable emulgel formulations. All formulations exhibited non-Newtonian shear-thinning properties which are desirable for topical applications. Both the release and permeation rates decreased with increasing viscosity and rigidity of the formulation. The lower the complex modulus of the emulgels, the higher the steady-state flux of the drug through the skin. Adding Sepineo P600 to emulgel systems resulted in increased rheological properties, which in turn slowed the diffusion of the drug for in vitro release. Although as expected skin permeation was rate limiting since in vitro release was 3 to 4 log-fold faster than skin flux. However, an interesting finding was that the derived skin/vehicle partition coefficient suggested the ionic interaction between lidocaine and Sepineo polymer reducing the free drug, i.e., thermodynamic activity and hence the flux with increasing Sepineo P600 concentration. Overall, this study has provided us with valuable insights into understanding the relationship between the microstructure (rheology), physical stability and skin drug delivery properties which will help to design and optimize topical emulgel formulations.

Sustainable Alternatives to Petroleum-Derived Excipients in Pharmaceutical Oil-in-Water Creams

Recently, vast efforts towards sustainability have been made in the pharmaceutical industry. In conventional oil-in-water (O/W) cream formulations, various petroleum-based excipients, namely mineral oil and petrolatum, are commonly used. Natural or synthetic excipients, derived from vegetable sources, were explored as alternatives to petroleum-based excipients in prototype topical creams, with 1% (w/w) lidocaine. A conventional cream comprised of petroleum-derived excipients was compared to creams containing sustainable excipients in terms of key quality and performance attributes, physicochemical properties, and formulation performance. The petrolatum-based control formulation had the highest viscosity of 248.0 Pa·s, a melting point of 42.7°C, a low separation index at 25°C of 0.031, and an IVRT flux of 52.9 µg/cm2/h. Formulation SUS-4 was the least viscous formulation at 86.9 Pa·s, had the lowest melting point of 33.6°C, the highest separation index of 0.120, and the highest IVRT flux of 139.4 µg/cm2/h. Alternatively, SUS-5 had a higher viscosity of 131.3 Pa·s, a melting point of 43.6°C, a low separation index of 0.046, and the lowest IVRT flux of 25.2 µg/cm2/h. The cumulative drug permeation after 12 h from SUS-4, SUS-5, and the control were 126.2 µg/cm2, 113.8 µg/cm2, and 108.1 µg/cm2, respectively. The composition of the oil-in-water creams had influence on physicochemical properties and drug release; however, skin permeation was not impacted. Sustainable natural or synthetic excipients in topical cream formulations were found to be suitable alternatives to petroleum-based excipients with comparable key quality attributes and performance attributes and should be considered during formulation development.

The Global Bioequivalence Harmonisation Initiative (GBHI): Report of the fifth international EUFEPS/AAPS conference

The series of conferences of the Global Bioequivalence Harmonisation Initiative (GBHI) was started in 2015 by the European Federation for Pharmaceutical Sciences (EUFEPS). All GBHI meetings so far were co-organised together with the American Association of Pharmaceutical Scientists (AAPS). Beginning with the 3rd workshop US-FDA joined as co-sponsor - to support global harmonisation of regulatory recommendations for bioequivalence (BE) assessment. At the 5th GBHI conference, the following BE topics were intensively discussed, and the following main conclusions were drawn: (1) Statistical considerations for BE assessment in specific situations covering scaling approaches for highly variable drug (HVD) products, two-stage adaptive design and opportunities of modelling and simulation to support BE: even though special BE study concepts like adaptive designs are not often used in practise so far, a majority of the workshop participants were in favour of a more frequent application of such approaches. The regulatory conditions relevant in this context need further concretisation and harmonisation between the regions. Moreover, modelling and simulation were considered as a promising and evolving approach, also for BE development programmes. (2) Fed versus fasting conditions in BE trials: Findings that BE between generic products could be confirmed only after fasted administration but failed under fed conditions seem more an exception than the rule. Obviously, BCS class IV compounds are most problematic in this context. Differences in critical excipients such as surfactants or pH-modifiers may be relevant reasons for different sensitivity for interactions in fasted versus fed conditions. Consequently, such deviations in composition of generic preparations should be avoided. Moreover, confirmation of BE may be generally difficult comparing different dosage forms, such like capsules versus tablets, especially in fed state. (3) BE assessment of locally acting drug products applied topically to the skin: Appropriateness and potential benefit of in-vitro tests as alternatives to clinical efficacy studies have been comprehensively discussed. In addition to the already well-established in-vitro release and permeation tests, other techniques were suggested, e.g., Raman spectroscopy or dermal open flow microperfusion. Validation of those methods is challenging and, despite significant progress already achieved during previous years, more research is needed before they may be fully accepted for regulatory purposes. (4) BE evaluation of narrow therapeutic index (NTI) drugs: The discrepancies amongst regulatory agencies in necessity of tighter BE acceptance ranges, the recommendations for inclusion of peak and total drug exposure into BE assessment with more restrictive criteria and the importance of comparison of the product-related within-subject variability for NTI drugs were debated. Arguments in favour and against the different approaches were presented and discussed but need further consideration before harmonisation can be achieved. The highly interactive meeting and extensive exchange between regulators and scientists from industry and academia resulted in useful progress in open BE issues and supported the goal of science-driven harmonisation.

Regulatory Requirements for the Development of Second-Entry Semisolid Topical Products in the European Union

The development of second-entry topical products is hampered by several factors. The excipient composition should be similar to the reference product because excipients may also contribute to efficacy. Conventional pharmacokinetic bioequivalence studies were not considered acceptable because drug concentrations are measured downstream after the site of action. There was no agreed methodology to characterize the microstructure of semisolids, and waivers of therapeutic equivalence studies with clinical endpoints were not possible. Only the vasoconstrictor assay for corticosteroids was accepted as a surrogate. This paper describes the implementation of the European Union's stepwise approach for locally acting products to cutaneous products, discusses the equivalence requirements of the EMA Draft Guideline on the Quality and Equivalence of Topical Products, and compares them with the US Food and Drug Administration recommendations. Step 1 includes the possibility of waivers for simple formulations based on in vitro data only (Q1 + Q2 + Q3 + IVRT). Step 2 includes step 1 requirements plus a kinetic study (TS/IVPT/PKBE) to compare the local availability of complex formulations. Step 3 refers to clinical studies with pharmacodynamic/clinical endpoints. As excipients may affect the local tolerability and efficacy of the products, the similarity of excipient composition is required in all steps, except where clinical endpoints are compared.

API-polymer interactions in Sepineo P600 based topical gel formulation- impact on rheology

In the present study, topical gel and emulsion gel were formulated using Acrylamide/ Sodium Acryloyldimethyl taurate copolymer (Sepineo P600) as a gelling agent, and their rheological attributes and physical stability were evaluated upon incorporation of API. Lidocaine, a free base drug (pK_a 7.92) was used as a model drug in all formulations. Medium- chain Triglycerides (MCT) was used as a dispersed phase to prepare the emulgel. Results show that the rheological properties of both gel and emulgel such as viscosity, elastic moduli and yield stress were significantly influenced by the pH of the topical formulations and API concentration. A lower pH (pH < pKa) leads to the increase in number of cationic species of lidocaine, which results in the weakening of the structure of the gel matrix by charge screening of polymer-polymer repulsions. Interactions between API and polymer chains through electrostatic attraction may play a major role in altering the rheology, which could potentially impact the physical stability against phase separation of the internal phase in emulsion gel samples. This study provides valuable insights into rheological behaviors of Sepineo P600 gel and emulgel which can be modified or tuned though the interplay of the API properties and critical formulation parameters such as pH. The tunable rheological properties with simpler manufacturing process make Sepineo P600 gel and emulsion gel very suitable systems for use in semisolid topical formulations.

Phenytoin-loaded bioactive nanoparticles for the treatment of diabetic pressure ulcers: formulation and in vitro/in vivo evaluation

Drug repurposing offers the chance to explore the full potential of existing drugs while reducing drug development time and costs. For instance, the anticonvulsant drug phenytoin (PHT) has been investigated for its wound healing properties. However, its poor solubility and variability of doses used topically limit its use. Hence, the aim of this study was to improve the properties and wound healing efficacy of PHT for the treatment of diabetic bedsores. PHT was encapsulated, using a modified ionic gelation method, in either positively or negatively charged chitosan-alginate nanoparticles (NPs), which possess previously demonstrated wound healing potential. These NPs were characterized by transmission electron microscopy, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. PHT-loaded NPs were evaluated in vivo for their pressure ulcers' healing potential using diabetic rats. The prepared NPs, especially the positively charged particles, exhibited superior wound healing efficacy compared to PHT suspension, with respect to healing rates, granulation tissue formation, tissue maturation, and collagen content. The positively charged NPs resulted in a 56.54% wound closure at day 7, compared to 37% for PHT suspension. Moreover, skin treated with these NPs showed a mature dermis structure with skin appendages, which were absent in all other groups, in addition to the highest collagen content of 63.65%. In conclusion, the use of a bioactive carrier enhanced the healing properties of PHT and allowed the use of relatively low doses of the drug. Our findings suggest that the prepared NPs offer an effective antibiotic-free delivery system for diabetic wound healing applications.

Determination of Microstructural Impact on the Release of Drug from Hydroxypropyl Cellulose Gel by Validated In Vitro Release Test Method

Microstructure of a semisolid system is greatly influenced by the formulation composition and the processing parameters. Different polymers exhibit different three-dimensional structure and these have a great impact on the drug release properties. The current research focuses on studying the impact of hydroxypropyl cellulose gel microstructure on the release properties of chlorhexidine gluconate (CHX G). The two main investigating methods of microstructure were used namely, rheology and texture analysis to determine the differences in the formulations studied. The CHX G drug release study was performed using a developed and validated in vitro release test method, which is reproducible, discriminative, and robust to detect the formulation differences. The drug release results showed that there was appreciable difference in the release rates of the different formulations. The rheology and texture analysis data correlated well with the difference in the release rates. The formulations differences were further confirmed by a statistical approach using analysis of variance.

Portable and automated analyzer for rapid and high precision in vitro dissolution of drugs

We developed a novel portable and automated dissolution test analyzer for rapid and high precision in vitro dissolution testing of drugs. The analyzer consists of a flow-through-cell drug dissolution system, an automated sequential sampling system, a high-speed capillary electrophoresis (HSCE) system, and a data acquisition system. Combining the high-temporal resolution flow-gating sampling approach with HSCE, which has outstanding advantages of efficient separation and resolution, the analyzer can achieve rapid analysis and exhibits the ability in miniaturization for on-site assessment of different active pharmaceutical ingredients. To integrate the flow-through-cell dissolution system with HSCE, a specially designed flow-gating-injection (FGI) interface was employed. The performance of the analyzer was investigated by analyzing the dissolution of immediate-release drugs including single dose (amoxicillin dispersible tablets) and fixed dose combination (amoxicillin and clavulanate potassium) drug tablets with the high-temporal resolutions of 12 s and 20 s, respectively. The dissolution profiles of different active pharmaceutical ingredients could be simultaneously and automatically monitored with high repeatability and accuracy. The analyzer was successfully utilized for the pharmaceutical quality control and bio-relevant dissolution testing, as well as in vivo-in vitro correlation analysis. Our portable analyzer is miniaturized, convenient and of low-cost, and will provide a valuable tool for dissolution testing in pharmaceutical research and development.

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Portable automated analyzer for rapid and high precision dissolution of drugs.

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Miniaturized, low-cost and battery-powered with high repeatability and accuracy.

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Successful applications in QC, bio-relevant dissolution and IVIVC analysis of drugs.

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Universal applicability for both immediate-release and fixed dose combination drugs.

The Implications of Regulatory Framework for Topical Semisolid Drug Products: From Critical Quality and Performance Attributes towards Establishing Bioequivalence

Due to complex interdependent relationships affecting their microstructure, topical semisolid drug formulations face unique obstacles to the development of generics compared to other drug products. Traditionally, establishing bioequivalence is based on comparative clinical trials, which are expensive and often associated with high degrees of variability and low sensitivity in detecting formulation differences. To address this issue, leading regulatory agencies have aimed to advance guidelines relevant to topical generics, ultimately accepting different non-clinical, in vitro/in vivo surrogate methods for topical bioequivalence assessment. Unfortunately, according to both industry and academia stakeholders, these efforts are far from flawless, and often upsurge the potential for result variability and a number of other failure modes. This paper offers a comprehensive review of the literature focused on amending regulatory positions concerning the demonstration of (i) extended pharmaceutical equivalence and (ii) equivalence with respect to the efficacy of topical semisolids. The proposed corrective measures are disclosed and critically discussed, as they span from mere demands to widen the acceptance range (e.g., from ±10% to ±20%/±25% for rheology and in vitro release parameters highly prone to batch-to-batch variability) or reassess the optimal number of samples required to reach the desired statistical power, but also rely on specific data modeling or novel statistical approaches.

Influence of Inter- and Intra-Batch Variability on the Sample Size Required for Demonstration of Equivalent Microstructure of Semisolid Dosage Forms

Inter- and intra-batch variability of the quality attributes contribute to the uncertainty for demonstrating equivalent microstructure of post-approval changes and generic/hybrids of semisolid topical products. Selecting a representative sample size to describe accurately the in vitro properties of semisolids and to reach enough statistical power to demonstrate similarity between two semisolid topical products is currently challenging. The objective of this work is to establish the number of batches and units per batch to be compared based on different inter-batch and intra-batch variability to demonstrate equivalence in the physical characteristics of the products that ensure a similar microstructure of the semisolid. This investigation shows that the minimum number of batches to be compared of each product is 3 and the minimum number of units per batch could be 6 in the case of low intra- and inter-batch variability. If the products are not identical, i.e., 2.5–5% differences that are expected due to differences in the manufacturing process or the suppliers of excipients, 12 units and 6 batches are needed. If intra- or inter-batch variability is larger than 10%, the number of batches and/or the number of units needs to be increased. As the interplay between inter- and intra-batch variability is complex, the sample size required for each combination of inter- and intra-batch variability and expected difference between products can be obtained in the attached tables.

Diving into Batch-to-Batch Variability of Topical Products-a Regulatory Bottleneck

PURPOSE

Following the recent European Medicine Agency (EMA) draft guideline on quality and equivalence of topical products, a modular framework for bioequivalence assessment is proposed, wherein the qualitative, quantitative, microstructure and product performance sameness is demanded to support generic applications. Strict regulatory limits are now imposed, but, the suitability of these limits has been subject of intense debate. In this context, this paper aims to address these issues by characterizing a panel of 8 reference blockbuster semisolid topical products.

METHODS

For each product, three batches were selected and, whenever possible, batches retrieved from different manufacturing sites were considered. Product microstructure was evaluated in terms of globule size, pH, rheological attributes and, if required, the thermal behaviour was also assessed. Performance was evaluated through in vitro release testing (IVRT). Finally, an integrated multivariate analysis was performed to highlight the features that most contribute for product variability.

RESULTS

Marked differences were registered within reference products. Statistical analysis demonstrated that if EMA criteria are applied, none of the same product batches can be considered as equivalent. Rheological parameters as well as IVRT indicators account for the majority of batch-to-batch differences.

CONCLUSIONS

Semisolid dosage forms exhibit intrinsic variability. This calls for the attention to the need of establishing reasonable equivalence criteria applied to generic drug products. Graphical abstract.

Rheology by Design: A Regulatory Tutorial for Analytical Method Validation

The increasing demand for product and process understanding as an active pursuit in the quality guideline Q8 and, more recently, on the draft guideline on quality and equivalence of topical products, has unveiled the tremendous potential of rheology methods as a tool for microstructure characterization of topical semisolid dosage forms. Accordingly, procedure standardization is a dire need. This work aimed at developing and validating a methodology tutorial for rheology analysis. A 1% hydrocortisone cream was used as model cream formulation. Through a risk assessment analysis, the impact of selected critical method variables (geometry, temperature and application mode) was estimated in a broad range of rheological critical analytical attributes-zero-shear viscosity, upper-shear thinning viscosity, lower-shear thinning viscosity, infinite-shear viscosity, rotational yield point, thixotropic relative area, linear viscoelastic region, oscillatory yield point, storage modulus, loss modulus, and loss tangent. The proposed validation of the approach included the rheometer qualification, followed by the validation of numerous operational critical parameters regarding a rheology profile acquisition. The thixotropic relative area, oscillatory yield point, flow point and viscosity related endpoints proved to be highly sensitive and discriminatory parameters. This rationale provided a standard framework for the development of a reliable and robust rheology profile acquisition.