An analysis of multidrug multicomponent crystals as tools for drug development

In a typical tablet or capsule formulation, the active drug is often present as a crystalline solid. This solid emerges from the relationships between the individual atoms within the crystal, which confer a distinct set of physical properties. Then, it follows that if we modify the packing arrangement of the individual molecules within these crystals, we can modulate their properties. This can be achieved by crystal engineering. Crystal engineering has also seen teams arrange multiple drug molecules within the same crystal, resulting in dramatic improvements to drug properties in the lab. The success of drugs like SEGLENTIS® and Entresto® have revitalised interest in these forms, but controversy surrounding their translation has prompted this reconsideration of their clinical utility. I reflect on the current academic, clinical, and commercial interest in multidrug multicomponent crystals, drawing parallels with developments pre-Bragg, contributing to a nuanced understanding of the potential and limitations of crystal engineering in pharmaceutical applications.

Molecular complexes of drug combinations: A review of cocrystals, salts, coamorphous systems and amorphous solid dispersions

As the advancements in the medical technology and healthcare develop through the years, combinational therapy has evolved to be an important treatment modality in many disease settings, including cancer, cardiovascular disease and infectious diseases. In an effort to alleviate "pill burden" and improve patient compliance, fixed dose combinations (FDCs) have been developed to be used as effective therapeutics. Among all FDCs, the category of drug-drug molecular complexes has been proven an efficient methodology in designing and treating diseases, with many drugs being approved. Among all drug-drug molecular complexes, drug-drug cocrystals, salts, coamorphous systems and solid dispersions have been successfully developed and many have been approved by the FDA. In this review, we dwell deeply into the molecular mechanisms behind the different types of drug-drug molecular complexes, including the key functional groups involved in the intermolecular interactions, the applications of each category of molecular complexes, as well as the advantages and challenges thereof. This comprehensive review provides useful insights into the practical design and manufacture of drug-drug molecular complexes and points out the future direction for the development of new advantageous combinational therapies that benefit more patients.

First cocrystal of esculetin: simultaneously optimized in vitro/vivo properties and antioxidant effect

Esculetin (ELT) is one of the best-known and simplest coumarins with powerful natural antioxidant effects but insoluble and difficult to absorb. In order to overcome the problems, cocrystal engineering was first applied to ELT in this paper. Nicotinamide (NAM) was selected as the coformer for its excellent water solubility and potential synergistic antioxidant effect with ELT. The structure of the ELT-NAM cocrystal was successfully prepared and characterized by IR, SCXRD, PXRD, and DSC-TG. Furthermore, the in vitro/vivo properties and antioxidant effects of the cocrystal were adequately studied. The results highlight that the ELT obtained tremendous improvements in water solubility and bioavailability after cocrystal formation. Meanwhile, the synergistic enhancement of ELT with NAM in antioxidant effect was demonstrated by the DPPH assay. Ultimately, the simultaneously optimized in vitro/vivo properties and antioxidant activity of the cocrystal created an improved practical effect of hepatoprotective in rat experiments. The investigation is significant for developing coumarin drugs represented by ELT.

Structure-property relations of a unique and systematic dataset of 19 isostructural multicomponent apremilast forms

The structure-property relations are examined for apremilast cocrystals and solvates in this work. A unique and large dataset of multicomponent crystal forms is presented including 7 cocrystals and 12 solvates. In total, 15 of the presented multicomponent forms and their crystal structures are published here for the first time. This dataset is unique owing to the extreme crystal packing similarity of all 19 crystal forms. This fact makes the evaluation of structure-property relations significantly easier and more precise since the differences in the crystal lattice arrangement are close to negligible. Properties of the guest molecules used here can be directly correlated with the macroscopic properties of the corresponding multicomponent forms. Interestingly, a considerable correlation was found between the intrinsic dissolution rate of the multicomponent forms and their solubility, as well as the solubility of their guest molecules in the dissolution medium. The latter is of particular interest as it can aid in the design of multicomponent forms with tuned properties.

Unlocking the potential of drug-drug cocrystals - A comprehensive review

Intensive research subjected to the improvement of solubility and bioavailability of certain drugs has popularized the formation of cocrystals, wherein the desired drug is non-ionically bonded to a coformer by means of weak bonds. This paper addresses how crystal engineering of two compatible drug components can enhance the physicochemical and therapeutic properties of either or both of the drugs, resulting in drug-drug cocrystals, with pertinent examples. The paper also discusses the continuous screening processes which are replacing the traditional methods of crystallization due to numerous benefits to the producer as well as the products. Although faced with certain regulatory and scale-up constraints, cocrystals provide immense opportunities to the field of novel drug development.

Solid-State and Particle Size Control of Pharmaceutical Cocrystals using Atomization-Based Techniques

Poor bioavailability and aqueous solubility represent a major constraint during the development of new API molecules and can influence the impact of new medicines or halt their approval to the market. Cocrystals offer a novel and competitive advantage over other conventional methods with respect towards the substantial improvement in solubility profiles relative to the single-API crystals. Furthermore, the production of such cocrystals through atomization-based methods allow for greater control, with respect to particle size reduction, to further increase the solubility of the API. Such atomization-based methods include supercritical fluid methods, conventional spray drying and electrohydrodynamic atomization/electrospraying. The influence of process parameters such as solution flow rates, pressure and solution concentration, in controlling the solid-state and final particle size are discussed in this review with respect to atomization-based methods. For the last decade, literature has been attempting to catch-up with new regulatory rulings regarding the classification of cocrystals, due in part to data sparsity. In recent years, there has been an increase in cocrystal publications, specifically employing atomization-based methods. This review considers the benefits to employing atomization-based methods for the generation of pharmaceutical cocrystals, examines the most recent regulatory changes regarding cocrystals and provides an outlook towards the future of this field.

Energy framework and solubility: a new predictive model in the evaluation of the structure–property relationship of pharmaceutical solid forms

Crystal structures with lower interaction energy tend to present higher aqueous solubility.

Solid State Characterization and Dissolution Enhancement of Nevirapine Cocrystals

Purpose: Novel cocrystals of nevirapine (NP) were designed and prepared with salicylamide and 3-hydroxy benzoic acid (3-HBA).

Methods: The cocrystals were prepared by solvent drop grinding method by adding few drops of acetone to enhance the solubility and dissolution. The drug and cocrystals were characterized by differential scanning calorimetry (DSC) and powder x-ray diffraction (PXRD). The solubility of NP, its wet ground form, and cocrystals were investigated at different pH. Moreover, the effect of surfactant on solubility of cocrystals was also studied. Finally, intrinsic dissolution rate (IDR) and stability of cocrystals was examined.

Results: The characterization of cocrystals by DSC and PXRD revealed formation of new solid forms due to changes in thermogram and PXRD pattern. The cocrystal of NP with 3-HBA showed 4.5 folds greater solubility in pH 1.2 buffer and 5.5 folds in 1% Tween 80 as compared to original drug. IDR of cocrystals was higher than the pure drug in 0.1 N hydrochloric acid (HCl). Moreover, cocrystals were found physically stable after 3 months as evident from unchanged IDR.

Conclusion: Hence, the present research indicates the new stable solid forms of NP with improved dissolution rate than pure drug.

Isostructural cocrystals of metaxalone with improved dissolution characteristics

Muscle relaxant and pain reliever metaxalone (MET) is a biopharmaceutical classification systems (BCS) class II drug with poor aqueous solubility and high permeability. The presence of an aromatic skeleton and cyclic carboxamate moiety are the probable reasons for the decreased aqueous solubility, which impacts on its low bioavailability. A high dose (800 mg) of the drug often creates adverse side effects on the central nervous system that needs urgent remedy. Cocrystallization of MET with nicotinamide (NAM), salicylamide (SAM), and 4-hydroxybenzoic acid (HBA) resulted in multicomponent solids that were characterized by PXRD, DSC and single crystal X-ray diffraction. Cocrystals with SAM and NAM form 2D isostructural cocrystals, whereas with HBA the result is a differently packed cocrystal hydrate (or anisole hemisolvate) depending upon the crystallization medium. Similar to the reported MET cocrystals, these cocrystals also confirm the preference for an imide⋯imide homosynthon in the drug. The dominance of the drug–drug homodimer over drug-coformer heterodimers was demonstrated based on binding energy calculations. Further, powder dissolution experiments in pH 6.8 phosphate buffer indicate that the cocrystals improved the apparent solubility compared to the native drug by 3–9 fold. The absence of stronger heterosynthons between MET and the coformers, their lower melting points and the high solubility of the coformers are the probable reasons for the enhanced solubility of the bioactive component. The MET–NAM cocrystal exhibited the highest solubility/dissolution rate among the three binary solid forms, which may offer improved bioavailability and a lower dose with minimal side effects.

Metaxalone forms isostructural cocrystals with nicotinamide and salicylamide that offer a solubility advantage compared to the native drug. A drug–drug homosynthon is retained in all the cocrystal structures.

Challenges and opportunities of pharmaceutical cocrystals: a focused review on non-steroidal anti-inflammatory drugs

The focus of the review is to discuss the relevant and essential aspects of pharmaceutical cocrystals in both academia and industry with an emphasis on non-steroidal anti-inflammatory drugs (NSAIDs). Although cocrystals have been prepared for a plethora of drugs, NSAID cocrystals are focused due to their humongous application in different fields of medication such as antipyretic, anti-inflammatory, analgesic, antiplatelet, antitumor, and anti-carcinogenic drugs. The highlights of the review are (a) background of cocrystals and other solid forms of an active pharmaceutical ingredient (API) based on the principles of crystal engineering, (b) why cocrystals are an excellent opportunity in the pharma industry, (c) common methods of preparation of cocrystals from the lab scale to bulk quantity, (d) some latest case studies of NSAIDs which have shown better physicochemical properties for example; mechanical properties (tabletability), hydration, solubility, bioavailability, and permeability, and (e) latest guidelines of the US FDA and EMA opening new opportunities and challenges.

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.

Co-processing of Atorvastatin and Ezetimibe for Enhanced Dissolution Rate: In Vitro and In Vivo Correlation

Development of fixed dose combinations is growing and many of these drug combinations are being legally marketed. However, the development of these requires careful investigation of possible physicochemical changes during co-processing. This requires investigation of the effect of co-processing of drug combination in absence of excipients to maximize the chance of interaction (if any). Accordingly, the aim was to investigate the effect of co-processing of ezetimibe and atorvastatin on drugs dissolution rate. The objective was extended to in vitro in vivo correlation. Drugs were subjected to wet co-processing in presence of ethanol after being mixed at different ratios. The prepared formulations were characterized using FTIR spectroscopy, X-ray powder diffraction, differential scanning calorimetry, scanning electron microscopy, and in vitro dissolution testing. These investigations proved the possibility of eutectic system formation after drugs co-processing. This was reflected on drugs dissolution rate which was significantly enhanced at dose ratio and 2:1 atorvastatin:ezetimibe molar ratio compared to the corresponding pure drugs. In vivo antihyperlipidemic effects of the co-processed drugs were monitored in albino mice which were subjected to hyperlipidemia induction using poloxamer 407. The results showed significant enhancement in pharmacological activity as revealed from pronounced reduction in cholesterol level in mice administering the co-processed form of both drugs. Besides, histopathological examinations of the liver showed marked decrease in hepatic vacuolation. In conclusion, co-processing of atorvastatin with ezetimibe resulted in beneficial eutexia which hastened the dissolution rate and pharmacological effects of both drugs.Graphical abstract.

Cocrystallization of axitinib with carboxylic acids: preparation, crystal structures and dissolution behavior

Three cocrystals of axitinib were prepared, and they demonstrated a significantly improved apparent solubility and dissolution rate without compromising physical stability.

Cocrystals of regorafenib with dicarboxylic acids: synthesis, characterization and property evaluation

Three cocrystals of regorafenib were synthesized, and two of them demonstrate significantly improved solubility and tabletability without compromising physicochemical stability.

Crystal Structures, Stability, and Solubility Evaluation of a 2:1 Diosgenin-Piperazine Cocrystal

A cocrystal of diosgenin with piperazine in 2:1 stoichiometry was successfully synthesized. The solid form was prepared by liquid assisted grinding, slurry and crystallization methods. The cocrystal was characterized by powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and structure determined by single crystal X-ray diffraction, the hydrogen bonds formed into fish bone structure along the [010] direction and all the molecules packed into 3D layer structure along a axis. After formation of cocrystal, the solubility of diosgenin was improved, and the solubility value in 0.2% SDS solution was approximately 1.5 times as large as that of the parent material.

Drug-drug cocrystals: Opportunities and challenges

Recently, drug-drug cocrystal attracts more and more attention. It offers a low risk, low-cost but high reward route to new and better medicines and could improve the physiochemical and biopharmaceutical properties of a medicine by addition of a suitable therapeutically effective component without any chemical modification. Having so many advantages, to date, the reported drug-drug cocrystals are rare. Here we review the drug-drug cocrystals that reported in last decade and shed light on the opportunities and challenges for the development of drug-drug cocrystals.

Analytical Methods for Determination of Apremilast from Bulk, Dosage Form and Biological Fluids: A Critical Review

Apremilast is an anti-inflammatory agent. It has been a flourishing molecule in the field of dermatology. In the year 2014, Apremilast got its approval for treatment of psoriatic arthritis. Presently it is known to treat a number of other conditions, including atopic dermatitis and plaque psoriasis. Apremilast a phthalimide derivative, is non-hygroscopic in nature. It is practically insoluble in water. Apremilast acts by inhibiting the activity of phosphodiesterase 4 (PDE4), an intracellular enzyme. Analytical method plays a key role to understand the physio-chemical properties of a drug molecule. Because of poor solubility and low permeability, analytical method development and formulation becomes challenging. Till date, there are no standard test methods available to analyze Apremilast. So, a critical review of the analytical techniques of Apremilast was carried out. The literature search was done by screening the papers reporting analytical techniques of Apremilast from year 2014 to 2019. Methodologies particularly UV spectroscopy, HPTLC, HPLC, X-ray diffraction, NMR, LC-MS were collected and reviewed. Interminable efforts are made by the researchers to develop simple, accurate, robust and cost-effective methods of analysis. In pharmaceutical research, this information will aid in the development of new delivery systems. The review will prove beneficial and advantageous pre-formulation studies and will guide the formulation development.

Progress on cocrystallization of poorly soluble NME's in the last decade

Cocrystallization of pharmaceuticals has been an exciting field of interest to both academia and industries, demonstrated from its increasing growth rate of publications, patents, and marketed formulations.

A 5-fluorouracil–kaempferol drug–drug cocrystal: a ternary phase diagram, characterization and property evaluation

A drug–drug cocrystal of 5-fluorouracil and kaempferol was comprehensively investigated and exhibits optimized solubility behavior in comparison with individual APIs.

Complex methodology for rational design of Apremilast-benzoic acid co-crystallization process

A new co-crystal of pharmaceutical active ingredient Apremilast was successfully designed in this work. The discovered co-crystal with benzoic acid significantly improves key properties like the dissolution and stability of an otherwise poorly soluble Apremilast. A crystallization process was developed, which includes efficient solvent selection and ternary phase diagram construction to minimize risks during scale up. To increase efficiency, we propose that both steps be combined into a single methodology based on solubility data. A suitable solvent for the co-crystallization process was selected and ternary phase diagrams were constructed using three different modifications of thermodynamic model of solid-liquid equilibria. Based on the obtained information, the co-crystallization process was scaled-up to 100 mL. This provides a feasible process to produce larger amounts of this promising pharmaceutical solid form of Apremilast necessary for further drug development.

Understanding the formation of apremilast cocrystals

Apremilast (APR), an anti-psoriatic agent, easily forms isostructural cocrystals and solvates with aromatic entities, often disobeying at the same time Kitaigorodsky's rule as to the saturation of possible hydrogen-bonding sites. In this paper the reasons for this peculiar behavior are investigated, employing a joint experimental and theoretical approach. This includes the design of cocrystals with coformers having a high propensity towards the formation of both aromatic-aromatic and hydrogen-bonding interactions, determination of their structure, using solid-state NMR spectroscopy and X-ray crystallography, as well as calculations of stabilization energies of formation of the obtained cocrystals, followed by crystal structure prediction calculations and solubility measurements. The findings indicate that the stabilization energies of cocrystal formation are positive in all cases, which results from strain in the APR conformation in these crystal forms. On the other hand, solubility measurements show that the Gibbs free energy of formation of the apremilast:picolinamide cocrystal is negative, suggesting that the formation of the studied cocrystals is entropy driven. This entropic stabilization is associated with the disorder observed in almost all known cocrystals and solvates of APR.

Drug–drug salts of mefenamic acid\tolfenamic acid and piperazine to improve physicochemical properties for potential veterinary use

Drug–drug salts of mefenamic acid\tolfenamic acid and piperazine were designed to improve the solubility and hygroscopicity, which could possibly extend the drug–drug salt form into veterinary use.