Solid dispersions of efonidipine hydrochloride ethanolate with improved physicochemical and pharmacokinetic properties prepared with microwave treatment

Improved drug transfer into brain tissue via the "nose-to-brain" approach using suspension or powder formulations based on the amorphous solid dispersion technique

Intranasal administration has attracted increasing attention as a drug delivery approach based on nose-to-brain drug delivery from the nasal cavity to brain tissue directly, bypassing the blood-brain barrier. However, application of the method to poorly water-soluble drugs is potentially limited due to low aqueous solubility and dissolution, which can hinder drug transfer to brain tissue. In the present study, we focused on an amorphous solid dispersion (ASD) technique to improve drug dissolution. A carbamazepine-loaded ASD model drug was prepared using the solvent evaporation method (ASD-1). After screening six water-soluble polymer carriers, polyvinyl alcohol (PVA)-based ASD-1 formulation exhibited the most rapid and highest drug dissolution under experimental conditions in the nasal cavity (pH 6.0). A carbamazepine suspension dispersed with a PVA-ASD-1 formulation exhibited enhanced drug delivery into plasma and brain tissue of rats in vivo. A spray-dried powder formulation of PVA-ASD (PVA-ASD-2) exhibited improved drug dissolution and in vivo drug transfer. Our key finding is that the spray-dried PVA-ASD-2 formulation exhibited higher brain/plasma ratios than the PVA-ASD-1 suspension formulation. Our physical characterization data and demonstration of improved drug transfer suggest that ASD-based intranasal formulations hold promise for drug delivery to the brain.

Pharmaceutical amorphous solid dispersion: A review of manufacturing strategies

Amorphous solid dispersions (ASDs) are popular for enhancing the solubility and bioavailability of poorly water-soluble drugs. Various approaches have been employed to produce ASDs and novel techniques are emerging. This review provides an updated overview of manufacturing techniques for preparing ASDs. As physical stability is a critical quality attribute for ASD, the impact of formulation, equipment, and process variables, together with the downstream processing on physical stability of ASDs have been discussed. Selection strategies are proposed to identify suitable manufacturing methods, which may aid in the development of ASDs with satisfactory physical stability.

RP-HPLC method development and validation for the quantification of Efonidipine hydrochloride in HME processed solid dispersions

Background

Efonidipine hydrochloride (EFO) is a poorly water-soluble drug and, hence, has poor bioavailability. Solid dispersions (SDs) of EFO using Eudragit EPO were prepared using hot-melt extrusion (HME) for the first time. The current study aims at developing a simple RP-HPLC method to quantify EFO in the developed SDs.

Results

The chromatographic separation was carried out on an Agilent Eclipsed XDB-C18 column (4.6 × 250 mm), packed with 5 μm particles. The optimized mobile phase consisted of HPLC grade acetonitrile and 0.020 mol/L KH2PO4 (pH 2.5) buffer in the ratio of 85:15 v/v with a flow rate optimized at 1.2 ml/min. The developed method was validated for system suitability, linearity, accuracy, precision, and robustness. The linearity results showed an excellent linear relationship between the drug concentration and peak area, indicating the peak area is directly proportional to the analyte concentration within a specific range and an excellent correlation coefficient of 0.9998. Intermediate precision and repeatability confirmed that the method provides precise results with %RSD value less than 2% for EFO. The assay results of the developed formulations were in the acceptable range with RSD less than 2%. The enhanced drug dissolution from the Eudragit EPO carrier with 10% Citric Acid (CA) is attributed to the conversion of the drug from crystalline to amorphous form, and microenvironmental acidic pH provided by CA.

Conclusion

In a nutshell, the developed RP-HPLC method showed excellent ability to differentiate the formulations and highlights the role of the polymer and the plasticizer.

Graphical abstract

Microwave-Induced In Situ Amorphization: A New Strategy for Tackling the Stability Issue of Amorphous Solid Dispersions

The thermodynamically unstable nature of amorphous drugs has led to a persistent stability issue of amorphous solid dispersions (ASDs). Lately, microwave-induced in situ amorphization has been proposed as a promising solution to this problem, where the originally loaded crystalline drug is in situ amorphized within the final dosage form using a household microwave oven prior to oral administration. In addition to circumventing issues with physical stability, it can also simplify the problematic downstream processing of ASDs. In this review paper, we address the significance of exploring and developing this novel technology with an emphasis on systemically reviewing the currently available literature in this pharmaceutical arena and highlighting the underlying mechanisms involved in inducing in situ amorphization. Specifically, in order to achieve a high drug amorphicity, formulations should be composed of drugs with high solubility in polymers, as well as polymers with high hygroscopicity and good post-plasticized flexibility of chains. Furthermore, high microwave energy input is considered to be a desirable factor. Lastly, this review discusses challenges in the development of this technology including chemical stability, selection criteria for excipients and the dissolution performance of the microwave-induced ASDs.

In Vitro-In Vivo Correlation for Solid Dispersion of a Poorly Water-Soluble Drug Efonidipine Hydrochloride

The aim of this present study was to investigate the ability of different dissolution methods to predict the in vivo performance of efonidipine hydrochloride (EFH). The solid dispersions of EFH were prepared by solvent evaporation method with HPMC-AS as matrix and urea as a pH adjusting agent. The paddle method, the open-loop, and the closed-loop flow-through cell methods were studied. In the study, Weibull's model was the best fit to explain release profiles. The pharmacokinetics behaviors of two kinds of solid dispersions with different release rate were investigated in comparison to the EFH after oral administration in rats. In vivo absorption was calculated by a numerical deconvolution method. In the study, the level A in vivo and in vitro correlation (IVIVC) was utilized. The correlation coefficient was calculated and interpreted by means of linear regression analysis (Origin.Pro.8.5 software). As a result, excellent IVIVC for solid dispersions and crude drug (r² = 0.9352-0.9916) was obtained for the dissolution rate determined with flow-through cell open-loop system in phosphate buffer solution with 0.1% (w/v) polysorbate 80 at pH 6.5, the flow-rate of 4 mL/min. In addition, the self-assembled flow cell system had good repeatability and accuracy. The dissolution rate of the solid dispersion could be slowed down by the flow-through method, and the difference caused by preparation was significantly distinguished. The study demonstrated that flow-through cell method of the open-loop, compared with paddle method, was suitable for predicting in vivo performance of EFH solid dispersions.

Effect of preparation method on the surface properties and UV imaging of indomethacin solid dispersions

This work explores the use of UV imaging in solid dispersion systems. Solid dispersions are one of the common strategies used in improving the dissolution of poorly soluble drugs. Three manufacturing techniques (spray drying (SD), freeze drying (FD) and homogenising (HG)) are investigated. Differential Scanning Calorimetry (DSC) and X-Ray Powder Diffraction (XRPD) was used in characterising the solid dispersions. Advanced imaging was implemented to give an insight into how these solid dispersions performed. The DSC and XRPD results showed that all three methods and the various ratios studied produced amorphous solid dispersions. Ultra-Violet (UV) imaging of the pseudo Intrinsic Dissolution Rate (IDR) deduced only two samples to have superior pseudo IDR values to the IDR of the parent drug indomethacin (INDO). The whole dose imaging of the capsule formulation however showed all the samples (SD, FD and HG) to have superior dissolution to that of INDO which was in contrast to the IDR results. The UV images obtained from the determination of the pseudo IDR also showed a phenomenon the authors are reporting for the first time where increased polymer (Soluplus) content produced "web-like" strands that migrated to the top of the quartz cell which may have been responsible for the low pseudo IDR values. The authors also report for the first time using this UV imaging technique, the tip of a capsule coming off for drug to go into solution. The area under the curve suggested the best five samples dissolution wise to be 1:3 SD > 1:1 HG > 1:1 SD > 1:3 FD > 1:3 HG meaning a ratio of INDO to SOL in these dispersion of up to 1:3 being sufficient to produce significant dissolution increases. The developed interfacial (surface) area ratio (Sdr) highlighted how the surface area of the IDR compacts varied between the batches, in particular highlighting larger surface area gains for the FD and HG compacts. A choice of instrumentation/techniques to use in making solid dispersions may well come down to cost or instrument availability for a formulator as all three techniques were successful in improving the dissolution of indomethacin. This work thus highlights the importance of having both complimentary IDR and whole dosage imaging techniques in giving a better understanding of solid dispersion systems.

Pharmaceutical Dispersion Techniques for Dissolution and Bioavailability Enhancement of Poorly Water-Soluble Drugs

Over the past decades, a large number of drugs as well as drug candidates with poor dissolution characteristics have been witnessed, which invokes great interest in enabling formulation of these active ingredients. Poorly water-soluble drugs, especially biopharmaceutical classification system (BCS) II ones, are preferably designed as oral dosage forms if the dissolution limit can be broken through. Minimizing a drug’s size is an effective means to increase its dissolution and hence the bioavailability, which can be achieved by specialized dispersion techniques. This article reviews the most commonly used dispersion techniques for pharmaceutical processing that can practically enhance the dissolution and bioavailability of poorly water-soluble drugs. Major interests focus on solid dispersion, lipid-based dispersion (nanoencapsulation), and liquisolid dispersion (drug solubilized in a non-volatile solvent and dispersed in suitable solid excipients for tableting or capsulizing), covering the formulation development, preparative technique and potential applications for oral drug delivery. Otherwise, some other techniques that can increase the dispersibility of a drug such as co-precipitation, concomitant crystallization and inclusion complexation are also discussed. Various dispersion techniques provide a productive platform for addressing the formulation challenge of poorly water-soluble drugs. Solid dispersion and liquisolid dispersion are most likely to be successful in developing oral dosage forms. Lipid-based dispersion represents a promising approach to surmounting the bioavailability of low-permeable drugs, though the technique needs to traverse the obstacle from liquid to solid transformation. Novel dispersion techniques are highly encouraged to develop for formulation of poorly water-soluble drugs.

Quantification of microwave-induced amorphization of celecoxib in PVP tablets using transmission Raman spectroscopy

In this study, the influence of drug load on the microwave-induced amorphization of celecoxib (CCX) in polyvinylpyrrolidone (PVP) tablets was investigated using quantitative transmission Raman spectroscopy. A design of experiments (DoE) setup was applied for developing the quantitative model using two factors: drug load (10, 30, and 50% w/w) and amorphous fraction (0, 25, 50, 75 and 100%). The data was modeled using partial least-squares (PLS) regression and resulted in a robust model with a root mean-square error of prediction of 2.5%. The PLS model was used to study the amorphization kinetics of CCX-PVP tablets with different drug content (10, 20, 30, 40 and 50% w/w). For this purpose, transition Raman spectra were collected in 60 s intervals over a total microwave time of 10 min with an energy input of 1000 W. Using the quantitative model it was possible to measure the amorphous fraction of the tablets and follow the amorphization as a function of microwaving time. The relative amorphous fraction of CCX increased with increasing microwaving time and decreasing drug load, hence 90 ± 7% of the drug was amorphized in the tablets with 10% drug load whereas only 31 ± 7% of the drug was amorphized in the 50% CCX tablets. It is suggested that the degree of amorphization depends on drug loading. The likelihood of drug particles being in direct contact with the polymer PVP is a requirement for the dissolution of the drug into the polymer upon microwaving, and this is reduced with increasing drug load. This was further supported by polarized light microscopy that revealed evidence of crystalline particles and clusters in all the microwaved tablets.

Electron microscopy/energy dispersive X-ray spectroscopy of drug distribution in solid dispersions and interpretation by multifractal geometry

Much contemporary research of poorly water-soluble drugs focuses on amorphous solid dispersions (SDs) for oral drug delivery. Recently, a multifractal formalism has been introduced to describe the distribution of an inorganic carrier in SDs. The present work attempts to directly image model drugs by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. The compounds amlodipine, felodipine, glyburide, and indomethacine, which include halogens to enable sufficient scattering in energy dispersive X-ray spectroscopy, were employed to prepare SDs with hydroxypropyl methylcellulose acetate succinate (HPMCAS) by using a microwave method. Following chemical imaging, it was demonstrated that drug distribution was best described by multifractals, which was clearly superior to a monofractal assumption. The obtained fractal dimensions were influenced by drug loading and it was possible to detect microstructural changes upon addition of the plasticizer urea. Accordingly, the multifractal approach bears much potential to better explore the analytical results of chemical formulation imaging. Insights can be gained from the microstructural organization of SDs, which is interesting to further study formulation and process factors as well as physical stability.

Amorphization within the tablet: Using microwave irradiation to form a glass solution in situ

In situ amorphization is a concept that allows to amorphize a given drug in its final dosage form right before administration. Hence, this approach can potentially be used to circumvent recrystallization issues that other amorphous formulation approaches are facing during storage. In this study, the feasibility of microwave irradiation to prepare amorphous solid dispersions (glass solutions) in situ was investigated. Indomethacin (IND) and polyvinylpyrrolidone K12 (PVP) were tableted at a 1:2 (w/w) ratio. In order to study the influence of moisture content and energy input on the degree of amorphization, tablet formulations were stored at different relative humidity (32, 43 and 54% RH) and subsequently microwaved using nine different power-time combinations up to a maximum energy input of 90kJ. XRPD results showed that up to 80% (w/w) of IND could be amorphized within the tablet. mDSC measurements revealed that with increasing microwaving power and time, the fractions of crystalline IND and amorphous PVP reduced, whereas the amount of in situ formed IND-PVP glass solution increased. Intrinsic dissolution showed that the dissolution rate of the microwaved solid dispersion was similar to that of a quench cooled, fully amorphous glass solution even though the microwaved samples contained residual crystalline IND.