Influence of Polymers on the Physical and Chemical Stability of Spray-dried Amorphous Solid Dispersion: Dipyridamole Degradation Induced by Enteric Polymers

Polymer-inducing chemical degradation of amorphous solid dispersions driven by drug-polymer interactions for physical stabilization

Intermolecular interactions between active pharmaceutical ingredients (APIs) and carrier polymers are important for the long-term physical stability of amorphous solid dispersions (ASDs). However, the negative impact of intermolecular interactions on chemical stability has rarely been reported. In this study, the relationship between intermolecular interactions and physical and chemical stability was investigated using two ASDs composed of API and hydroxypropyl methylcellulose acetate succinate (HPMCAS) with different stabilities: ASD1 was physically stable but chemically unstable, whereas ASD2 was physically unstable but chemically stable. Ionic-bonding between the pyridine nitrogen in the API and succinyl group in HPMCAS was found in both ASDs. The additional interaction between the succinyl group in HPMCAS and the hydroxyl group in the API was suggested only in ASD1. It was concluded that the additional interaction contributed to the physical stability of ASD1; however, it accelerated the chemical reaction between the succinyl and hydroxyl groups to generate succinyl ester owing to its close proximity. This study shows that the intermolecular interaction between the API and carrier polymer is not always beneficial for chemical stability. Understanding the molecular states of APIs and polymers in ASDs is important for their successful development.

Role of Crystal Disorder and Mechanoactivation in Solid-State Stability of Pharmaceuticals

Common energy-intensive processes applied in oral solid dosage development, such as milling, sieving, blending, compaction, etc. generate particles with surface and bulk crystal disorder. An intriguing aspect of the generated crystal disorder is its evolution and repercussion on the physical- and chemical stabilities of drugs. In this review, we firstly examine the existing literature on crystal disorder and its implications on solid-state stability of pharmaceuticals. Secondly, we discuss the key aspects related to the generation and evolution of crystal disorder, dynamics of the disordered/amorphous phase, analytical techniques to measure/quantify them, and approaches to model the disordering propensity from first principles. The main objective of this compilation is to provide special impetus to predict or model the chemical degradation(s) resulting from processing-induced manifestation in bulk solid manufacturing. Finally, a generic workflow is proposed that can be useful to investigate the relevance of crystal disorder on the degradation of pharmaceuticals during stability studies. The present review will cater to the requirements for developing physically- and chemically stable drugs, thereby enabling early and rational decision-making during candidate screening and in assessing degradation risks associated with formulations and processing.

Forced Solid-State Oxidation Studies of Nifedipine-PVP Amorphous Solid Dispersion

In the present study, the oxidative degradation behavior of nifedipine (NIF) in amorphous solid dispersions (ASDs) prepared with poly(vinyl pyrrolidone) (PVP) with a short (K30) and a long (K90) chain length was investigated. The ASDs were prepared via dry ball-milling and analyzed using Fourier transform infrared (IR) spectroscopy, X-ray scattering, and differential scanning calorimetry. The ASDs were exposed to accelerated thermal-oxidative conditions using a pressurized oxygen headspace (120 °C for 1 day) and high temperatures at atmospheric pressure (60-120 °C for a period of 42 days). Additionally, solution-state oxidative degradation studies showed that pure NIF degrades to a greater extent than in the presence of PVP. Electronic structure calculations were performed to understand the impact of drug-polymer intermolecular interactions on the autoxidation of drugs. While no drug degradation was observed in freshly prepared ASD samples, alkyl free radicals were detected via electron paramagnetic resonance (EPR) spectroscopy. The free radicals were found to be consumed to a greater extent by PVP K30- than PVP K90-based ASDs upon exposure to high oxygen pressures. This was consistent with the greater solid-state oxidative degradation of NIF observed in ASDs with PVP K30 than with PVP K90. As no drug recrystallization occurred during this study period, the lower glass-transition temperature and presumed greater molecular mobility of PVP K30 and its ASD as compared to the PVP K90 system appear to contribute to the greater drug degradation in PVP-K30-based ASDs. The extent and the rate of oxidative degradation were higher in the case of PVP-K30-based ASD as compared to that in PVP-K90-based ASD, and the overall degradation increased with an increase in temperature. IR spectral analysis of drug-polymer interactions supports the electronic calculations of the oxidation process. We infer that, apart from the initial free radical content, the difference in the extent of drug-polymer intermolecular interactions in ASDs and amorphous stabilization during the forced oxidation experiments contribute to the observed differences in the autoxidative reactivity of the drug in ASDs with different PVP chain lengths. Overall, the chemical degradation of NIF in ASDs with two PVP chain lengths obtained from accelerated solid-state oxidation studies was in qualitative agreement with that obtained from long-term (3 years) storage under ambient conditions. The study highlights the ability of accelerated processes to determine the oxidative degradation behavior of polymeric ASDs and suggests that the polymer chain length could factor into chemical as well as physical stability considerations.

Impact of Polymer Type on Thermal Degradation of Amorphous Solid Dispersions Containing Ritonavir

High-temperature exposure during hot melt extrusion processing of amorphous solid dispersions may result in thermal degradation of the drug. Polymer type may influence the extent of degradation, although the underlying mechanisms are poorly understood. In this study, the model compound, ritonavir (T_m = 126 °C), undergoes thermal degradation upon high-temperature exposure. The extent of degradation of ritonavir in amorphous solid dispersions (ASDs) formulated with poly(vinylpyrrolidone) (PVP), poly(vinylpyrrolidone) vinyl acetate copolymer (PVP/VA), hydroxypropyl methylcellulose acetate succinate (HPMCAS), and hydroxypropyl methylcellulose (HPMC) following isothermal heating and hot melt extrusion was evaluated, and mechanisms related to molecular mobility and intermolecular interactions were assessed. Liquid chromatography-mass spectrometry (LC-MS/MS) studies were used to determine the degradation products and pathways and ultimately the drug-polymer compatibility. The dominant degradation product of ritonavir was the result of a dehydration reaction, which then catalyzed a series of hydrolysis reactions to generate additional degradation products, some newly reported. This reaction series led to accelerated degradation rates with protic polymers, HPMCAS and HPMC, while ASDs with aprotic polymers, PVP and PVP/VA, had reduced degradation rates. This work has implications for understanding mechanisms of thermal degradation and drug-polymer compatibility with respect to the thermal stability of amorphous solid dispersions.

Formulating a heat- and shear-labile drug in an amorphous solid dispersion: Balancing drug degradation and crystallinity

We seek to further addresss the questions posed by Moseson et al. regarding whether any residual crystal level, size, or characteristic is acceptable in an amorphous solid dispersion (ASD) such that its stability, enhanced dissolution, and increased bioavailability are not compromised. To address this highly relevant question, we study an interesting heat- and shear-labile drug in development, LY3009120. To study the effects of residual crystallinity and degradation in ASDs, we prepared three compositionally identical formulations (57–1, 59–4, and 59–5) using the KinetiSol process under various processing conditions to obtain samples with various levels of crystallinity (2.3%, 0.9%, and 0.1%, respectively) and degradation products (0.74%, 1.97%, and 3.12%, respectively). Samples with less than 1% crystallinity were placed on stability, and we observed no measurable change in the drug's crystallinity, dissolution profile or purity in the 59–4 and 59–5 formulations over four months of storage under closed conditions at 25 °C and 60% humidity. For formulations 57–1, 59–4, and 59–5, bioavailability studies in rats reveal a 44-fold, 55-fold, and 62-fold increase in mean AUC, respectively, compared to the physical mixture. This suggests that the presence of some residual crystals after processing can be acceptable and will not change the properties of the ASD over time.

Development of Apremilast Solid Dispersion Using TPGS and PVPVA with Enhanced Solubility and Bioavailability

Apremilast (APST) is an effective inhibitor of phosphodieasterase 4 (PDE4) which is the first oral drug for the treatment of adult patients with active psoriatic arthritis. However, Apremilast^'s low solubility restricts its dissolution and bioavailability. In this study, APST solid dispersion with D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) and Poly(1-vinylpyrrolidone-co-vinyl acetate) (PVPVA) was developed to improve the dissolution and bioavailability of APST by spray drying. A series of TPGS were synthesized to elucidate the effect of the ratio of monoester to diester on solubilizing capacity. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and Fourier transform infrared spectrophotometry (FT-IR) were used to characterize the solid dispersion, and the results showed that APST was amorphous in solid dispersion. In vitro dissolution study showed that the dissolution rate of solid dispersion in phosphate buffered saline (pH 6.8) was remarkably increased, reaching a release of 90% within 10 min. Moreover, in vivo pharmacokinetics study revealed that the bioavailability of solid dispersion in rats had significant improvement. In particular, its C_max and AUC_last were nearly 22- and 12.9-fold greater as compared to APST form B, respectively. In conclusion, APST solid dispersion with TPGS and PVPVA is an alternative drug delivery system to improve the solubility and oral bioavailability of APST.

Quaternary enteric solid dispersion prepared by hot-melt extrusion to mask the bitter taste and enhance drug stability

To mask the bitterness of drug is profoundly important especially in children's medication. This study designed and investigated a quaternary enteric solid dispersion (QESD) by secondary hot-melt-extrusion. Erythromycin (EM) was chosen as a model drug. The optimal QESD contained enteric polymer HPMCP-55, plasticizer and water-soluble polymer copovidone VA64. Raman and Atomic force microscope has exploited that majority EM was distributed in VA64 matrix, nanometer-sized EM-VA64 system was entrapped within enteric continuous phase to form a solid emulsion-like structure. For the prepared QESD, EM released concentration was far less than bitterness threshold (7 μg/mL to 20 μg/mL) in artificial saliva within the first 30 s. And dissolution rate was increased by 10% in article intestine fluid, which dominated by water-soluble VA64. Stress testing after two months at high-humidity (75% RH) and high-temperature (60 °C) revealed, compared with traditional enteric SDs, the chemical degradation of EM was slowed down in QESD. Furthermore, hydrogen and salt bonds were respectively formed between EM and VA64 and between leaking EM and HPMCP-55, which increasing the system stability and taste-masking. The effect of masking bitter taste can be satisfied as well as enhance drug dissolution rate in the intestine, and formulation physicochemical stability during storage.

Lyophilized Amorphous Dispersion of Telmisartan in a Combined Carrier-Alkalizer System: Formulation Development and In Vivo Study

Telmisartan suffers from low oral bioavailability due to its poor water solubility. The research work presents a formulation of solid dispersed (SD) telmisartan formulation as a ternary mixture of a drug, a polymeric carrier (poly(vinylpyrrolidone) (PVP) K30), and an alkalizer (Na₂CO₃). The preparation method, which was lyophilization of an aqueous solution containing the ingredients, was free from any organic solvent. The developed SD formulations resulted in a significant improvement in in vitro dissolution (>90% drug dissolution in 15 min) compared to pure telmisartan. Solid-state characterization by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) studies indicated the conversion of crystalline telmisartan into an amorphous form. Fourier transform infrared (FTIR) spectroscopy revealed the drug-polymer interaction that was responsible for reducing the chances of recrystallization. A short-term stability study showed that selected SD formulations were stable in terms of in vitro dissolution and retained their amorphous structure in ambient and accelerated conditions over 2 months. Selected formulations (drug/PVP K30/Na₂CO₃ as 1:1:2 or 1:2:2 weight ratio) resulted in >2.48 times relative oral bioavailability compared to marketed formulations. It was considered that the incorporation of an alkalizer and a hydrophilic polymer, and amorphization of telmisartan by lyophilization, could enhance in vitro dissolution and improve oral bioavailability.

Innovations in Thermal Processing: Hot-Melt Extrusion and KinetiSol® Dispersing

Thermal processing has gained much interest in the pharmaceutical industry, particularly for the enhancement of solubility, bioavailability, and dissolution of active pharmaceutical ingredients (APIs) with poor aqueous solubility. Formulation scientists have developed various techniques which may include physical and chemical modifications to achieve solubility enhancement. One of the most commonly used methods for solubility enhancement is through the use of amorphous solid dispersions (ASDs). Examples of commercialized ASDs include Kaletra®, Kalydeco®, and Onmel®. Various technologies produce ASDs; some of the approaches, such as spray-drying, solvent evaporation, and lyophilization, involve the use of solvents, whereas thermal approaches often do not require solvents. Processes that do not require solvents are usually preferred, as some solvents may induce toxicity due to residual solvents and are often considered to be damaging to the environment. The purpose of this review is to provide an update on recent innovations reported for using hot-melt extrusion and KinetiSol® Dispersing technologies to formulate poorly water-soluble APIs in amorphous solid dispersions. We will address development challenges for poorly water-soluble APIs and how these two processes meet these challenges.

Application of HPMC HME polymer as hot melt extrusion carrier in carbamazepine solid dispersion

AIM

This work is to investigate the application characteristics of a new hot melt extrusion (HME) polymer (HME-grade hydroxypropyl methylcellulose, namely HPMC HME 15LV) in solid dispersion by HME.

METHODS

Carbamazepine (CBZ) was chosen as the model drug. And two types of solid dispersion system was prepared by HME, that is, single carrier system which was composed of PVP VA64(VA64) or Soluplus (SOL), and binary carrier which was composed of HPMC HME 15LV and SOL. Phase analysis of the extrudates were characterized by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The dissolution, moisture absorption and thermal stability CBZ solid dispersion (CBZ-SD) were also investigated. In addition, the mechanism that affects the capsule dissolution was evaluated by the viscosity test and infiltration capability test.

RESULTS

CBZ-SD was prepared by HME. DSC and PXRD results indicated that CBZ was amorphous in all solid dispersions. Unlike CBZ-SD powder with high dissolution, CBZ-SD capsules showed the variable gelatinization phenomenon during dissolution and different dissolution behaviors, which can be interpreted by the viscosity test and infiltration capacity test. Furthermore, compared with single carrier system, CBZ-SD made by binary carrier exhibited lower moisture absorption and better thermal stability, which is benefit to the long-term stability of CBZ-SD.

CONCLUSION

HPMC HME 15LV, as a new HME carrier, has certain advantages in producing well CBZ-SD preparation. Its low viscosity can prevent the gelatinization phenomenon during capsule dissolution, as well as suitable T_g and low hygroscopicity were also benefit to the stability of CBZ-SD.

Hypromellose - A traditional pharmaceutical excipient with modern applications in oral and oromucosal drug delivery

Hydroxypropylmethylcellulose (HPMC), also known as Hypromellose, is a traditional pharmaceutical excipient widely exploited in oral sustained drug release matrix systems. The choice of numerous viscosity grades and molecular weights available from different manufacturers provides a great variability in its physical-chemical properties and is a basis for its broad successful application in pharmaceutical research, development, and manufacturing. The excellent mucoadhesive properties of HPMC predetermine its use in oromucosal delivery systems including mucoadhesive tablets and films. HPMC also possesses desirable properties for formulating amorphous solid dispersions increasing the oral bioavailability of poorly soluble drugs. Printability and electrospinnability of HPMC are promising features for its application in 3D printed drug products and nanofiber-based drug delivery systems. Nanoparticle-based formulations are extensively explored as antigen and protein carriers for the formulation of oral vaccines, and oral delivery of biologicals including insulin, respectively. HPMC, being a traditional pharmaceutical excipient, has an irreplaceable role in the development of new pharmaceutical technologies, and new drug products leading to continuous manufacturing processes, and personalized medicine. This review firstly provides information on the physical-chemical properties of HPMC and a comprehensive overview of its application in traditional oral drug formulations. Secondly, this review focuses on the application of HPMC in modern pharmaceutical technologies including spray drying, hot-melt extrusion, 3D printing, nanoprecipitation and electrospinning leading to the formulation of printlets, nanoparticle-, microparticle-, and nanofiber-based delivery systems for oral and oromucosal application. Hypromellose is an excellent excipient for formulation of classical dosage forms and advanced drug delivery systems. New methods of hypromellose processing include spray draying, hot-melt extrusion, 3D printing, and electrospinning.

Processing of Polyvinyl Acetate Phthalate in Hot-Melt Extrusion-Preparation of Amorphous Solid Dispersions

The preparation of amorphous solid dispersions (ASDs) is a suitable approach to overcome solubility-limited absorption of poorly soluble drugs. In particular, pH-dependent soluble polymers have proven to be an excellently suitable carrier material for ASDs. Polyvinyl acetate phthalate (PVAP) is a polymer with a pH-dependent solubility, which is as yet not thoroughly characterized regarding its suitability for a hot-melt extrusion process. The objective of this study was to assess the processability of PVAP within a hot-melt extrusion process with the aim of preparing an ASD. Therefore, the influence of different process parameters (temperature, feed-rate) on the degree of degradation, solid-state and dissolution time of the neat polymer was studied. Subsequently, drug-containing ASDs with indomethacin (IND) and dipyridamole (DPD) were prepared, respectively, and analyzed regarding drug content, solid-state, non-sink dissolution performance and storage stability. PVAP was extrudable in combination with 10% (w/w) PEG 3000 as plasticizer. The dissolution time of PVAP was only slightly influenced by different process parameters. For IND no degradation occurred in combination with PVAP and single phased ASDs could be generated. The dissolution performance of the IND-PVAP ASD at pH 5.5 was superior and at pH 6.8 equivalent compared to commonly used polymers hydroxypropylmethylcellulose acetate succinate (HPMCAS) and Eudragit L100-55.

Preparation and evaluation of gastro-floating hollow adhesive microspheres of carbomer/ethyl cellulose encapsulating dipyridamole

Gastro-floating hollow adhesive microspheres of Carbomer/ethyl cellulose encapsulating dipyridamole were fabricated and evaluated in vitro and in vivo.