Bioavailability assessment in the development phase of a drug product is vital to reveal the disadvantageous properties of the substance and the possible technological interventions. However, in vivo pharmacokinetic studies provide strong evidence for drug approval applications. Human and animal studies must be designed on the basis of preliminary biorelevant experiments in vitro and ex vivo. In this article, the authors have reviewed the recent methods and techniques from the last decade that are in use for assessing the bioavailability of drug molecules and the effects of technological modifications and drug delivery systems. Four main administration routes were selected: oral, transdermal, ocular, and nasal or inhalation. Three levels of methodologies were screened for each category: in vitro techniques with artificial membranes; cell culture, including monocultures and co-cultures; and finally, experiments where tissue or organ samples were used. Reproducibility, predictability, and level of acceptance by the regulatory organizations are summarized for the readers.

Background: Menopause is characterised by a decline in oestrogen levels, leading to physical and psychological symptoms that significantly affect quality of life. Current parenteral oestradiol ester therapies, while effective, are often associated with side effects due to their oil-based formulations, including injection-site reactions and immune responses. Methods: In this study, we developed a water-soluble, polyethylene glycol cross-linked β-cyclodextrin (PEG–β-CD) polymer-based system for parenteral oestradiol delivery and evaluated its biocompatibility, solubility enhancement, immune compatibility, and pharmacokinetics. Results: Cytotoxicity assays using NIH-3T3 fibroblasts and RAW 264.7 macrophages showed minimal toxicity up to 10% (w/w). Phase-solubility studies demonstrated a significant increase in oestradiol solubility with the PEG–β-CD polymer, surpassing that of β-cyclodextrin or PEG alone. Dynamic light scattering and FTIR analyses confirmed successful complex formation, with submicron particles averaging 271 nm and physical incorporation of oestradiol into the polymer matrix. Macrophage activation assays and RT-qPCR analyses indicated an absence of immunogenic responses or pro-inflammatory cytokine induction. In vivo toxicity testing in Galleria mellonella larvae confirmed safety, while pharmacokinetic studies in Wistar rats revealed rapid initial absorption followed by stable, low-level serum concentrations comparable to those of commercially used oestradiol esters. Conclusions: These findings indicate that the PEG–β-CD polymer–oestradiol complex provides a safe, water-based alternative to traditional oil-based injections, with the potential to reduce side effects and improve patient compliance in postmenopausal hormone therapy.

Multiparticulate dosage forms are becoming more popular than single-unit forms because they offer benefits such as more consistent gastric emptying, a lower chance of dose dumping, and flexible drug release patterns [1]. Among the available production methods, extrusion-spheronization is preferred because it can handle high amounts of active ingredients without creating large particles, and it also allows for the easy combination of multiple drugs in one unit at any ratio [2]. The aim of this research is to determine the optimal parameters of the extruder, namely, the screw rotation speed, liquid addition rate and powder feeding rate, to determine the independent process parameters of the spheroniser, and to measure the loss-on-drying values, particle size distribution, and morphology of extrudates. The required machines to produce pellets are a twin-screw extruder, a spheroniser, a peristaltic pump, and a cooling system. Extrudates were obtained by using a mixture of microcrystalline cellulose, corn starch, lactose monohydrate and 10% povidone solution.

Background: Cyclodextrin (CD) polymers have attracted increasing attention due to their favourable drug delivery properties and broad pharmaceutical applicability. While the bioavailability and biological behaviour of native cyclodextrins have been extensively investigated, considerably less information is available regarding modified cyclodextrin polymers. Therefore, the present study aimed to investigate the permeation and cellular uptake of an epichlorohydrin-crosslinked β-cyclodextrin polymer using multiple in vitro and ex vivo models. Methods: Fluorescently labelled β-cyclodextrin polymers were applied in all experiments. Membrane permeation studies were performed using an in-line diffusion cell system with membranes of different pore sizes. In vitro transport and cellular uptake were investigated on HaCaT, Caco-2, and TR146 cell monolayers, while ex vivo permeation studies were carried out using skin, buccal, and intestinal tissues. Results: The results demonstrated a strong size-dependent transport behaviour across synthetic membranes. Cell monolayer studies revealed cell-line-dependent differences in polymer intracellular distribution. Lysosomal accumulation was observed in HaCaT and Caco-2 cells, whereas no intracellular accumulation was detected in TR146 cells. These findings suggest differences in polymer permeation among the investigated cell models. Ex vivo studies demonstrated the tissue permeation of cyclodextrin polymers, with marked accumulation within skin layers, indicating predominant dermal retention. Furthermore, strong correlations were identified between the in vitro and ex vivo skin and intestinal models. Conclusions: Overall, the findings demonstrate that β-cyclodextrin polymers exhibit complex, barrier-dependent transport behaviour across different biological models. The observed differences in permeation and intracellular localization suggest that multiple transport processes may contribute to their biological interactions, which provide a foundation for future studies aimed at elucidating the molecular mechanisms governing polymer uptake and permeation.