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Pharmaceutical cocrystals are currently gaining interest among the scientific community, due to their great potential for providing novel crystalline forms with superior properties such as solubility, dissolution rate, bioavailability, and stability. Robust computational tools are valuable tools in the rationalization of cocrystal formation, by providing insight into the intermolecular interactions of multicomponent molecular solids. In this study, various computational techniques based on charge density analysis were implemented to assess structural and energetical perspectives of the interactions responsible for the formation and stability of entacapone-theophylline-water (ETP-THP-water, 1:1:1). Significant non-covalent interactions (NCIs) were identified and evaluated by Hirshfeld surface analysis and density functional theory (DFT) computations, and three-dimensional networks (energy vector diagrams, lattice energy frameworks) were constructed, outlining the crucial stabilizing role of water and the dominance of π-π stacking interactions in the cocrystal. Furthermore, thermal dehydration studies confirmed the strong binding of water molecules in the crystal lattice, as expressed by the high activation energy.

Polyelectrolyte polymers have been widely used in the pharmaceutical field as excipients to facilitate various drug delivery systems. Polyelectrolytes have been used to modulate the electrostatic environment and enhance favorable interactions between the drug and the polymer in amorphous solid dispersions (ASDs) prepared mainly by hot-melt extrusion. Polyelectrolytes have been used alone, or in combination with nonionic polymers as interpolyelectrolyte complexes, or after the addition of small molecular additives. They were found to enhance physical stability by favoring stabilizing intermolecular interactions, as well as to exert an antiplasticizing effect. Moreover, they not only enhance drug dissolution, but they have also been used for maintaining supersaturation, especially in the case of weakly basic drugs that tend to precipitate in the intestine. Additional uses include controlled and/or targeted drug release with enhanced physical stability and ease of preparation via novel continuous processes. Polyelectrolyte matrices, used along with scalable manufacturing methods in accordance with green chemistry principles, emerge as an attractive viable alternative for the preparation of ASDs with improved physical stability and biopharmaceutic performance.

Sildenafil is a potent selective, reversible inhibitor of phosphodiesterase type 5 (PDE5) approved for the treatment of erectile dysfunction and pulmonary arterial hypertension. Whilst twenty years have passed since its original approval by the US Food and Drug Administration (USFDA), sildenafil enters the fourth industrial era catalyzing the treatment advances against erectile dysfunction and pulmonary hypertension. The plethora of detailed clinical data accumulated and the two sildenafil analogues marketed, namely tadalafil and vardenafil, signify the relevant therapeutic and commercial achievements. The pharmacokinetic and pharmacodynamic behavior of the drug appears complex, interdependent and of critical importance whereas the treatment of special population cohorts is considered. The diversity of the available formulation strategies and their compatible administration routes, extend from tablets to bolus suspensions and from per os to intravenous, respectively, inheriting the associated strengths and weaknesses. In this comprehensive review, we attempt to elucidate the multi-disciplinary elements spanning the knowledge fields of chemical synthesis, physicochemical properties, pharmacology, clinical applications, biopharmaceutical profile, formulation approaches for different routes of administration and analytical strategies, currently employed to guide the development of sildenafil-based compositions.