Particle size reduction is a commonly used process to improve the solubility and the dissolution of drug formulations. The solubility of a drug in the gastrointestinal tract is a crucial parameter, because it can greatly influence the bioavailability. This work provides a comprehensive investigation of the effect of the particle size, pH, biorelevant media and polymers (PVA and PVPK-25) on the solubility and dissolution of drug formulations using three model compounds with different acid-base characteristics (papaverine hydrochloride, furosemide and niflumic acid). It was demonstrated that micronization does not change the equilibrium solubility of a drug, but it results in a faster dissolution. In contrast, nanonization can improve the equilibrium solubility of a drug, but the selection of the appropriate excipient used for nanonization is essential, because out of the two used polymers, only the PVPK-25 had an increasing effect on the solubility. This phenomenon can be explained by the molecular structure of the excipients. Based on laser diffraction measurements, PVPK-25 could also inhibit the aggregation of the particles more effectively than PVA, but none of the polymers could hold the nanonized samples in the submicron range until the end of the measurements.

Absorption through the skin of topically applied chemicals is relevant for both formulation development and safety assessment, especially in the early stages of development. However, the supply of human skin is limited, and the traditional in vitro methods are of low throughput. As an alternative, an artificial membrane-based Skin Parallel Artificial Membrane Permeability Assay (Skin-PAMPA) has been developed to mimic the permeability through the stratum corneum. In this study, this assay was used to measure the permeability of a model compound, 4-phenylethyl-resorcinol (PER), dissolved in 13 different solvents that are commonly used in cosmetic formulation development. The study was performed at concentrations close to the saturated solution of PER in each solvent to investigate the maximum thermodynamic potential of the solvents. The permeability of PER in selected solvents was also measured on ex vivo pig skin for comparison. Pig ear skin is an accepted alternative model of human skin. The permeability coefficient, which is independent of the concentration of the applied solution, showed a good correlation (R² = 0.844) between the Skin-PAMPA and the pig skin permeation data. Our results support the use of the Skin-PAMPA to screen the suitability of different solvents for non-polar compounds at an early stage of formulation development.

Creating supersaturating drug delivery systems to overcome the poor aqueous solubility of active ingredients became a frequent choice for formulation scientists. Supersaturation as a solution phenomenon is, however, still challenging to understand, and therefore many recent publications focus on this topic. This work aimed to investigate and better understand the pH dependence of supersaturation of telmisartan (TEL) at a molecular level and find a connection between the physicochemical properties of the active pharmaceutical ingredient (API) and the ability to form supersaturated solutions of the API. Therefore, the main focus of the work was the pH-dependent thermodynamic and kinetic solubility of the model API, TEL. Based on kinetic solubility results, TEL was observed to form a supersaturated solution only in the pH range 3–8. The experimental thermodynamic solubility-pH profile shows a slight deviation from the theoretical Henderson–Hasselbalch curve, which indicates the presence of zwitterionic aggregates in the solution. Based on pK_a values and the refined solubility constants and distribution of macrospecies, the pH range where high supersaturation-capacity is observed is the same where the zwitterionic form of TEL is present. The existence of zwitterionic aggregation was confirmed experimentally in the pH range of 3 to 8 by mass spectrometry.

Background/Objectives: Early diagnosis and oral or, in severe cases, intravenous antibiotics are usually effective for Lyme disease, but some patients have persistent symptoms unresponsive to standards of care, requiring alternative therapies. Disulfiram (DIS), a drug for alcoholism, is under investigation as a potential adjunctive treatment, but its low bioavailability, rapid metabolism, and safety concerns urge the development of improved formulations for clinical translation. Methods: Screening dissolution and permeation studies were investigated for vehicle and excipient selection, following the pharmacopeia perspectives to develop and optimize the low-dose DIS rectal suppository intended for application in post-treatment Lyme disease syndrome (PTLDS). Further characterizations were carried out by differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy. Results: Cyclodextrin (CD) encapsulation was investigated to improve the aqueous solubility of the hydrophobic drug. The dissolution of DIS from fatty base suppository was very slow; it was remarkably improved by the molecular encapsulation of the drug with CDs. The dissolution of DIS from a water-soluble base was more favorable, but incomplete. In the polyethylene glycol (PEG) based suppositories, the addition of CDs already in a physical mixture ensured the dissolution of the drug. The presented drug delivery system relates to a novel preparation for rectal administration comprising a low-dose disulfiram with improved solubility and permeability by the PEG and hydroxypropyl-β-cyclodextrin (HPBCD) synergistic matrix. Conclusions: The rectal dosage form containing the drug and CD in the physical mixture is advantageous, avoiding the hepatic first-pass effect, minimizing dose-limiting toxicity, simplifying production, and fasting the availability of the repositioned drug.