Comparisons of in Vitro Models to Evaluate the Membrane Permeability of Amorphous Drug Nanoparticles.

The spontaneous formation of amorphous drug nanoparticles following the release of a drug from a supersaturating formulation is gaining increasing attention due to their potential contribution to increased oral bioavailability. The formation of nanosized drug particles also has considerable implications for the interpretation of in vitro and in vivo data. However, the membrane transport properties of these drug particles remain less well understood. Herein, the membrane permeation of nanosized amorphous drug particles of a model drug atazanavir was evaluated using different artificial membrane-based, cell-based, and animal tissue-based models. Results showed that flux enhancement by particles was different for the various systems used. Generally, good agreement was obtained among experiments performed using the same apparatus with different model membranes, with the exception of the Madin-Darby canine kidney cell monolayer and the Long-Evans rat intestine tissue, which showed lower flux enhancements. Franz cell-based models showed slightly higher flux enhancements by particles compared to Transwell and intestinal tissue sac models. Mass transport analysis suggested that the extent of flux enhancement by particles is dependent on the geometry of the apparatus as well as the properties of the membrane and buffer used, whereas the flux plateau concentration is dependent on the unstirred water later (UWL) asymmetry. These results highlight the complexity in characterizing the permeability advantage of these nonmembrane permeable drug particles and suggest that caution should be used in selecting the appropriate in vitro model to evaluate the overall permeability of colloidal drug particles.

Mechanisms and Extent of Enhanced Passive Permeation by Colloidal Drug Particles.

Formulations containing nanosized drug particles such as nanocrystals and nanosized amorphous drug aggregates recently came into light as promising strategies to improve the bioavailability of poorly soluble drugs. However, the increased solubility due to the reduction in particle size cannot adequately explain the enhanced bioavailability. In this study, the mechanisms and extent of enhanced passive permeation by drug particles were investigated using atazanavir, lopinavir, and clotrimazole as model drugs. Franz diffusion cells with lipid-infused membranes were utilized to evaluate transmembrane flux. The impact of stirring rate, receiver buffer condition, and particle size was investigated, and mass transport analyses were conducted to calculate transmembrane flux. Flux enhancement by particles was found to be dependent on particle size as well as the partitioning behavior of the drug between the receiver solution and the membrane, which is determined by both the drug and buffer used. A flux plateau was observed at high particle concentrations above amorphous solubility, confirming that mass transfer of amorphous drug particles from the aqueous solution to the membrane occurs only through the molecularly dissolved drug. Mass transport models were used to calculate flux enhancement by particles for various drugs at different conditions. Good agreements were obtained between experimental and predicted values. These results should contribute to improved bioavailability prediction of nanosized drug particles and better design of formulations containing colloidal drug particles.

pH-Dependent supersaturation from amorphous solid dispersions of weakly basic drugs.

PURPOSE: In amorphous solid dispersions (ASDs), the chemical potential of a drug can be reduced due to mixing with the polymer in the solid matrix, and this can lead to reduced drug release when the polymer is insoluble in the dissolution media. If both the drug and the polymer composing an ASD are ionizable, drug release from the ASD becomes pH-dependent. The goal of this study was to gain insights into the pH-dependent solubility suppression from ASD formulations. METHODS: The maximum release of clotrimazole, a weakly basic drug, from ASDs formulated with insoluble and pH-responsive polymers, was determined as a function of solution pH. Drug-polymer interactions in ASDs were probed using melting point depression, moisture sorption, and solid-state Nuclear Magnetic Resonance spectroscopy (SSNMR) measurements. RESULTS: The extent of solubility suppression was dependent on polymer type and drug loading. The strength of drug-polymer interactions was found to correlate well with the degree of solubility suppression. For the same ASD, the degree of solubility suppression was nearly constant across the solution pH range studied, suggesting that polymer-drug interactions in residual ASD solids was independent of solution pH. The total drug release agrees with the Henderson-Hasselbalch relationship if the suppressed amorphous solubility of the free drug is independent of solution pH. CONCLUSIONS: The mechanism of solubility suppression at different solution pHs appeared to be drug-polymer interactions in the solid-state, where the concentration of the free drug remains the same at variable pHs and the total drug concentration follows the Henderson-Hasselbalch relationship.

Development of Topical Gel of Methotrexate Incorporated Ethosomes and Salicylic Acid for the Treatment of Psoriasis.

BACKGROUND: There is an unmet need for optimized drug delivery system of psoriasis therapy because of various issues like adverse reaction, permeation problem associated with convention treatment (oral and topical) available for psoriasis. OBJECTIVE: The goal was to develop an ethosomal gel of methotrexate (MTX)-incorporated ethosomes and salicylic acid (SA) and to evaluate and study its ethosomal gel potential in Imiquimod-induced psoriasis animal model to treat symptoms of psoriasis. METHODS: MTX-SA ethosomal gel was prepared by the cold method given by Touitou et al. and optimized by comparing it with MTX ethosomal gel and drug solution. Particle size, zeta potential, entrapment efficiency, and ex-vivo study were selected as the critical quality checking attributes. Psoriatic Area and Severity Index (PASI) score & histopathological examination were done for checking Antipsoriatic potential of MTX-SA ethosomal gel by using the imiquimod-induced psoriasis model. RESULTS: Optimized MTX-SA exhibited a particle size of 376.04 ± 3.47nm, EE(Entrapment efficiency) of 91.77 ± 0.02%. At the end of 24h, MTX-SA ethosomal gel exhibited a slow and prolonged release of MTX (26.13 ± 1.61% versus 6.97 ± 0.06%) compared to MTX drug solution. It also attributes of 43% retention study as compared to drug solution (13%). Besides, it essentially decreased the PASI score with the recuperation of normalcy of the mice's skin, while the MTX-SA gel displayed indications of gentle hyper and parakeratosis toward the completion of investigation when contrasted with the blank gel. CONCLUSION: The developed MTX-SA ethosomal gel formulation can be a promising alternative to existing MTX formulation in topically treating psoriasis.