Amorphous Solid Dispersions of Felodipine and Nifedipine with Soluplus®: Drug-Polymer Miscibility and Intermolecular Interactions

Effects of hypromellose acetate succinate on recrystallization inhibition, miscibility, and dissolution enhancement of baloxavir marboxil solid dispersions

Solid dispersions (SDs) have emerged as a promising strategy to enhance the solubility and bioavailability of poorly soluble active pharmaceutical ingredients. However, SDs tend to recrystallize unless suitable excipients are utilized. This study aimed to facilitate the rational selection of polymers and formulation design by evaluating the impact of various polymers on the miscibility, and phase behavior of SDs using baloxavir marboxil (BXM) with a high crystallization tendency as a model drug. Meanwhile, the effects of these polymers on the solubility enhancement and recrystallization inhibition were also assessed. The results indicated that the miscibility limit of BXM for HPMCAS was around 40 % drug loading (DL), whereas for PVP, PVPVA, and HPMC approximately 20 % DL. The BXM-HPC system exhibited limited miscibility with DL of 10 % or higher. BXM SDs based on various polymers exhibited varying degrees of spontaneous phase separation once DL exceeded the miscibility limit. Interestingly, a correlation was discovered between the phase separation behavior and the ability of the polymer to inhibit recrystallization. BXM-HPMCAS SDs exhibited optimal dissolution performance, compared with other systems. In conclusion, the physicochemical properties of polymers significantly influence BXM SDs performance and the BXM-HPMCAS SDs might promote an efficient and stable drug delivery system.

Review of industrially recognized polymers and manufacturing processes for amorphous solid dispersion based formulations

Evolving therapeutic landscape through combinatorial chemistry and high throughput screening have resulted in an increased number of poorly soluble drugs. Drug delivery strategies quickly adapted to convert these drugs into successful therapies. Amorphous solid dispersion (ASD) technology is widely employed as a drug delivery strategy by pharmaceutical industries to overcome the challenges associated with these poorly soluble drugs. The development of ASD formulation requires an understanding of polymers and manufacturing techniques. A review of US FDA-approved ASD-based products revealed that only a limited number of polymers and manufacturing technologies are employed by pharmaceutical industries. This review provides a comprehensive guide for the selection and overview of polymers and manufacturing technologies adopted by pharmaceutical industries for ASD formulation. The various employed polymers with their underlying mechanisms for solution-state and solid-state stability are discussed. ASD manufacturing techniques, primarily implemented by pharmaceutical industries for commercialization, are presented in Quality by Design (QbD) format. An overview of novel excipients and progress in manufacturing technologies are also discussed. This review provides insights to the researchers on the industrially accepted polymers and manufacturing technology for ASD formulation that has translated these challenging drugs into successful therapies.

Effects of Additives on the Physical Stability and Dissolution of Polymeric Amorphous Solid Dispersions: a Review

Polymeric amorphous solid dispersion (ASD) is a popular approach for enhancing the solubility of poorly water-soluble drugs. However, achieving both physical stability and dissolution performance in an ASD prepared with a single polymer can be challenging. Therefore, a secondary excipient can be added. In this paper, we review three classes of additives that can be added internally to ASDs: (i) a second polymer, to form a ternary drug-polymer-polymer ASD, (ii) counterions, to facilitate in situ salt formation, and (iii) surfactants. In an ASD prepared with a combination of polymers, each polymer exerts a unique function, such as a stabilizer in the solid state and a crystallization inhibitor during dissolution. In situ salt formation in ASD usually leads to substantial increases in the glass transition temperature, contributing to improved physical stability. Surfactants can enhance the wettability of ASD particles, thereby promoting rapid drug release. However, their potential adverse effects on physical stability and dissolution, resulting from enhanced molecular mobility and competitive molecular interaction with the polymer, respectively, warrant careful consideration. Finally, we discuss the impact of magnesium stearate and inorganic salts, excipients added externally upon downstream processing, on the solid-state stability as well as the dissolution of ASD tablets.

Effect of Buffer Salts on Physical Stability of Lyophilized and Spray-Dried Protein Formulations Containing Bovine Serum Albumin and Trehalose

This study examined the effect of buffer salts on the physical stability of spray-dried and lyophilized formulations of a model protein, bovine serum albumin (BSA). BSA formulations with various buffers were dried by either lyophilization or spray drying. The protein powders were then characterized using solid-state Fourier transform infrared spectroscopy (ssFTIR), powder X-ray diffraction (PXRD), size exclusion chromatography (SEC), solid-state hydrogen/deuterium exchange with mass spectrometry (ssHDX-MS), and solid-state nuclear magnetic resonance spectroscopy (ssNMR). Particle characterizations such as Brunauer-Emmett-Teller (BET) surface area, particle size distribution, and particle morphology were also performed. Results from conventional techniques such as ssFTIR did not exhibit correlations with the physical stability of studied formulations. Deconvoluted peak areas of deuterated samples from the ssHDX-MS study showed a satisfactory correlation with the loss of the monomeric peak area measured by SEC (R2 of 0.8722 for spray-dried formulations and 0.8428 for lyophilized formulations) in the 90-day accelerated stability study conducted at 40°C. mDSC and PXRD was unable to measure phase separation in the samples right after drying. In contrast, ssNMR successfully detected the occurrence of phase separation between the succinic buffer component and protein in the lyophilized formulation, which results in a distribution of microenvironmental acidity and the subsequent loss of long-term stability. Moreover, our results suggested that buffer salts have less impact on physical stability for the spray-dried formulations than the lyophilized solids.

High-throughput kinetic turbidity analysis for determination of amorphous solubility and excipient screening for amorphous solid dispersions

Many poorly water-soluble active pharmaceutical ingredients (APIs) rely on supersaturating formulations, such as amorphous solid dispersions (ASDs), to enhance oral bioavailability. ASDs kinetically trap amorphous solid drugs within polymer excipient matrices to maintain the amorphous drug states. The maximum solution concentration of the API in these formulations is known as the amorphous solubility. In early drug development with scarce material and time, high-throughput approaches to measuring amorphous solubility and screening excipient effects on crystallization risk offer significant benefits to preclinical formulation scientists. Here, we developed a high-throughput screening (HTS) workflow to quantify amorphous solubility and screen ASD excipients by automated kinetic turbidity analysis. Testing 20 model APIs with a wide range of biorelevant solubility, we demonstrated their apparent amorphous solubility determined by the HTS approach strongly correlated with quantification results using conventional liquid chromatography; while the real-time analysis significantly saved analytical time and experimental efforts. Furthermore, kinetic turbidity profiles elucidated distinct excipient effects on the precipitation process of APIs. These results were successfully translated to dissolution and precipitation behaviors of ASD formulations composed of the tested polymers. The high-throughput kinetic turbidity workflow presents a facile and information-rich approach for amorphous solubility screenings against excipients, and helps guide enabling formulation development.

Inhomogeneous Phase Significantly Reduces Oral Bioavailability of Felodipine/PVPVA Amorphous Solid Dispersion

Inhomogeneity is a key factor that significantly influences the dissolution behavior of amorphous solid dispersion (ASD). However, the underlying mechanisms of the effects of inhomogeneous phase on the dissolution characteristics as well as the bioavailability of ASDs are still unclear. In this study, two types of felodipine/PVPVA based ASDs with 30 wt % drug loading but different homogeneity were prepared: homogeneous "30 wt % ASD" prepared by spray drying, as well as inhomogeneous "30 wt % PM" prepared by physically mixing the sprayed dried 70 wt % ASD with PVPVA. We aimed to investigate (1) drug-polymer interaction mechanism and "apparent" interaction strength within the two ASDs and (2) dissolution mechanism as well as in vivo performance of the two ASDs. DSC thermogram revealing a single T_g in 30 wt % ASD confirmed its homogeneous phase. ¹H NMR, FT-IR, and DVS studies collectively proved that strong hydrogen bonding interactions formed between felodipine and PVPVA in ASDs. Moreover, homogeneous "30 wt % ASD" has more numbers of interacting drug-polymer pairs, and thus exhibits stronger "apparent" interaction strength comparing with that of inhomogeneous "30 wt % PM". Unexpectedly,in the in vitro dissolution studies, inhomogeneous "30 wt % PM" showed much faster dissolution and also generated drug concentration ∼4.4 times higher than that of homogeneous "30 wt % ASD". However, drug precipitate recrystallized much slower in homogeneous "30 wt % ASD", presumably because much more polymer coprecipitated with amorphous drug in this system, which helps inhibiting drug crystallization. Surprisingly, homogeneous "30 wt % ASD" showed a significantly higher bioavailability in the in vivo pharmacokinetic studies, with the maximum plasma concentrations (C_max) and the area under the curve (AUC) values of about 2.7 and 2.3 times higher than those of inhomogeneous "30 wt % PM". The above findings indicated that the amorphous state of drug precipitate contributes significantly to increase bioavailability of ASDs, while traditional in vitro dissolution studies, for instance, if we only compare the dissolved drug in solution or the capability of an ASD to generate supersaturation, are inadequate to predict in vivo performance of ASDs. In conclusion, the phase behavior of ASDs directly impact the formation of drug-polymer interaction, which controls not only drug supersaturation in solution but also drug crystallization in precipitate, and ultimately affect the in vivo performance of ASDs.

The role of hydrophilic/hydrophobic group ratio of polyvinyl alcohol on the miscibility of amlodipine in orodispersible films: From molecular mechanism study to product attributes

The miscibility of the therapeutic drug in the polymer matrix is the key to the successful design and development of orodispersible films (ODFs). In the present study, four hydrolyzed polyvinyl alcohols (PVAs) with identical polymerization degree were investigated as carriers for Amlodipine (AML) ODFs systematically. The drug-polymer miscibility and the intermolecular interaction were investigated by Flory-Huggins theory, Gordon-Taylor theory, molecular simulation, FTIR, Raman and ¹H NMR. The product attributes of ODFs were also studied. A pharmacokinetic study in rats was then conducted using the film product of PVA5-72, the best performer tested. The results revealed that the drug-polymer miscibility decreased linearly with the increase of hydrolyzed degree of PVA. Hydrogen bonds formed between the drug and the hydrophilic and hydrophobic groups of PVAs were the main intermolecular interaction that caused the differences in drug-polymer miscibility. Furthermore, drug-polymer interaction influenced the product attributes of ODFs, including dissolution profile, mechanical properties and physical stability. The pharmacokinetic study showed the ODFs disintegrated rapidly, and the amorphous AML dissolved and absorbed in the gastrointestinal tract, which was comparable to the commercial product. The research offered a foundation for development scientists in designing and formulating PVA films.

19F Solid-state NMR characterization of pharmaceutical solids

Solid-state NMR has been increasingly recognized as a high-resolution and versatile spectroscopic tool to characterize drug substances and products. However, the analysis of pharmaceutical materials is often carried out at natural isotopic abundance and a relatively low drug loading in multi-component systems and therefore suffers from challenges of low sensitivity. The fact that fluorinated therapeutics are well represented in pipeline drugs and commercial products offers an excellent opportunity to utilize fluorine as a molecular probe for pharmaceutical analysis. We aim to review recent advancements of ¹⁹F magic angle spinning NMR methods in modern drug research and development. Applications to polymorph screening at the micromolar level, structural elucidation, and investigation of molecular interactions at the Ångström to submicron resolution in drug delivery, stability, and quality will be discussed.

Amorphization of Drugs for Transdermal Delivery-a Recent Update

Amorphous solid dispersion is a popular formulation approach for orally administered poorly water-soluble drugs, especially for BCS class II. But oral delivery could not be an automatic choice for some drugs with high first-pass metabolism susceptibility. In such cases, transdermal delivery is considered an alternative if the drug is potent and the dose is less than 10 mg. Amorphization of drugs causes supersaturation and enhances the thermodynamic activity of the drugs. Hence, drug transport through the skin could be improved. The stabilization of amorphous system is a persistent challenge that restricts its application. A polymeric system, where amorphous drug is dispersed in a polymeric carrier, helps its stability. However, high excipient load often becomes problematic for the polymeric amorphous system. Coamorphous formulation is another approach, where one drug is mixed with another drug or low molecular weight compound, which stabilizes each other, restricts crystallization, and maintains a single-phase homogenous amorphous system. Prevention of recrystallization along with enhanced skin permeation has been observed by the transdermal coamorphous system. But scalable manufacturing methods, extensive stability study and in-depth in vivo evaluation are lacking. This review has critically studied the mechanistic aspects of amorphization and transdermal permeation by analyzing recent researches in this field to propose a future direction.

Hot Melt Extrusion-Triggered Amorphization as a Continuous Process for Inducing Extended Supersaturable Drug Immediate-Release from saSMSDs Systems

Hot melt extrusion (HME), a continuous manufacturing process for generating supersaturating amorphous self-micellizing solid dispersion systems (saSMSDs), holds promise for achieving amorphization of many pharmaceutical formulations. For saSMSDs generation, HME-triggered continuous processes offer advantages over traditional non-continuous processes such as fusion/quench cooling (FQC) and co-precipitation (CP). Here we employed HME, FQC, and CP to generate saSMSDs containing the water-insoluble BCS II drug nitrendipine (NIT) and self-micellizing polymer Soluplus^®. Scanning electron microscopy, powder X-ray diffraction, and differential scanning calorimetry results revealed that saSMSDs formed when NIT–Soluplus^® mixtures were subjected to the abovementioned amorphization methods. All saSMSDs outperformed crystalline NIT preparations and physical mixtures in achieving extended supersaturable immediate release states with superior solubility, “spring-parachute” process characteristics, and dissolution behaviors. Notably, Fourier transform-infrared spectroscopic results obtained for saSMSDs detected hydrogen bonding interactions between the drug and the carrier. Ultimately, our results revealed the advantages of HME-triggered amorphization as a continuous process for significantly improving drug dissolution, increasing solubility, and maintaining supersaturation as compared to traditional amorphization-based techniques.