Dose-Dependent Solubility-Permeability Interplay for Poorly Soluble Drugs under Non-Sink Conditions

Solid lipid nanoparticles for increased oral bioavailability of acalabrutinib in chronic lymphocytic leukaemia

Acalabrutinib (ACP) is a first-line treatment for chronic lymphocytic leukemia but suffers from poor and variable oral bioavailability due to its pH-dependent solubility, CYP3A4 metabolism, and P-gp efflux. Thus, the objective of this study was to improve the solubility and dissolution behaviour, in turn enhancing bioavailability, by formulating solid lipid nanoparticles (SLNs). ACP loaded SLNs (ACP-SLNs) were prepared via solvent-free hot emulsification followed by a double sonication process. A combination of glyceryl di-behenate and stearyl palmitate along with Tween 80 was used as the lipid phase to dissolve ACP. A 1% w/v Poloxomer188 solution served as the aqueous phase. The optimized ACP-SLNs were spherical in shape and had particle size of 234.7-257.5 nm, PDI of 0.261-0.320 and loading efficiency of 18.70 ± 1.78%. A typical biphasic release pattern was observed from ACP-SLNs in the in vitro dissolution studies under gastrointestinal and plasma pH conditions (> 90% drug release at pH 4.5 ± 0.2, 6.8 ± 0.2 (representing GIT), and 7.4 ± 0.2 (representing plasma) at 8, 16 and 24 h, respectively). The freeze-dried product was stable when stored at 5 °C for over 6 months. Compared with the bulk drug suspension, the ACP-SLNs suspension resulted in 2.29-fold increase in oral bioavailability and more importantly 2.46-fold increase in the distribution of drug to spleen. Additionally, inhibition of lymph production and flow by administering cycloheximide resulted in 46.01% decrease in the overall absorption of ACP-SLNs, indicating the significance of lymphatic uptake process in the oral absorption of ACP-SLNs.

Ex vivo permeability study of poorly soluble drugs across gastrointestinal membranes: acceptor compartment media composition

Ex vivo drug permeability testing across gastrointestinal (GI) membranes is crucial in drug discovery and oral drug delivery. It is a reliable method for drugs with good solubility, but it poses challenges for poorly soluble drugs, which are common in development pipelines today. Although enabling formulations increase the apparent solubility in the GI compartment (dissolution vessel or permeation chamber's donor compartment), maintaining solubilized drug in the acceptor compartment during ex vivo testing remains largely unresolved. This review compiles and critically evaluates the diverse compositions of acceptor media used in ex vivo permeability studies for poorly soluble drugs, highlighting this significant yet underexplored aspect of pharmaceutical science. An algorithm is proposed for selecting solubility-enhancing additives for the acceptor media in ex vivo permeability studies of poorly soluble drugs.

Novel First-Generation Dissolution Models to Investigate the Release and Uptake of Oral Lymphotropic Drug Products

Conventional dissolution tests only assess the aqueous release of drugs to ensure quality and performance, without indicating whether absorption occurs through the portal or the lymphatic circulation. To address this issue, this study aimed to develop novel first-generation dissolution models that could investigate the release and uptake of oral lymphotropic drugs and examine relevant formulation issues. Dissolution of three commercial lymphotropic drug products (Terbinafina, Apo-terbinafine, and Lamisil) was done using modified versions of USP Apparatus II and IV. The developed models contained a lymphatic compartment filled with artificial chylomicrons to account for absorption through intestinal lymphatic pathway. The various products exhibited different release profiles into the aqueous media and the lymphatic media across the two tested models. The modified USP IV apparatus demonstrated greater distinction in aqueous release patterns. However, the release pattern into the lymphatic media remained similar in both models. This work represents a progress in meeting the challenges posed by the increasing complexity of pharmaceutical products containing lipophilic drugs or formulations, and has the potential to contribute towards the development of in-vitro bioequivalence standards for formulations targeting intestinal lymphatics.

Ethanol-based solubility-enabling oral drug formulation development: Accounting for the solubility-permeability interplay

The aim of the current work was to investigate the key factors that govern the success/failure of an ethanol-based solubility-enabling oral drug formulation, including the effects of the ethanol on the solubility of the drug, the permeability across the intestinal membrane, the drug's dissolution in the aqueous milieu of the gastrointestinal tract (GIT), and the resulting solubility-permeability interplay. The concentration-dependent effects of ethanol-based vehicles on the solubility, the in-vitro Caco-2 permeability, the in-vivo rat permeability, and the biorelevant dissolution of the BCS class II antiepileptic drug carbamazepine were studied, and a predictive model describing the solubility-permeability relationship was developed. Significant concentration-dependent solubility increase of CBZ was obtained with increasing ethanol levels, that was accompanied by permeability decrease, both in Caco-2 and in rat perfusion studies, demonstrating a tradeoff between the increased solubility afforded by the ethanol and a concomitant permeability decrease. When ethanol absorption was accounted for, an excellent agreement was achieved between the predicted permeability and the experimental data. Biorelevant dissolution studies revealed that minimal ethanol levels of 30 % and 50 % were needed to fully dissolve 1 and 5 mg CBZ dose respectively, with no drug precipitation.In conclusion, key factors to be accounted for when developing ethanol-based formulation include the drug's solubility, permeability, the solubility-permeability interplay, and the drug dose intended to be delivered. Only the minimal amount of ethanol sufficient to solubilize the drug dose throughout the GIT should be used, and not more than that, to avoid unnecessarily permeability loss, and to maximize overall drug absorption.

Assessing the performance of thermally crosslinked amorphous solid dispersions with high drug loadings

Continuing what previous studies had also intended, the present study aims to shed light on some unanswered questions concerning a recently introduced class of high drug loading (HD) amorphous solid dispersions (ASDs), based on the in-situ thermal crosslinking of poly (acrylic acid) (PAA) and poly (vinyl alcohols) (PVA). Initially, the effect of supersaturated dissolution conditions on the kinetic solubility profiles of the crosslinked HD ASDSs having indomethacin (IND) as a model drug, was determined. Subsequently, the safety profile of these new crosslinked formulations was determined for the first time by evaluating their cytotoxic effect on human intestinal epithelia cell line (Caco-2), while their ex-vivo intestinal permeability was also studied via the non-everted gut sac method. According to the obtained findings, the in-situ thermal crosslinked IND HD ASDs present similar kinetic solubility profiles when the dissolution studies are conducted with a steady sink index value, regardless of the different dissolution medium's volume and the total dose of the API. Additionally, the results showed a concentration- and time- dependent cytotoxicity profile for all formulations, while the neat crosslinked PAA/PVA matrices did not elicit cytotoxicity during the first 24 h, even at the highest examined concentration. Finally, the newly proposed HD ASD system, resulted in a remarkably increased ex-vivo intestinal permeability of IND.

Non-Effective Improvement of Absorption for Some Nanoparticle Formulations Explained by Permeability under Non-Sink Conditions

We evaluated the in vitro permeability of nanoparticle formulations of high and low lipophilic compounds under non-sink conditions, wherein compounds are not completely dissolved. The permeability of the highly lipophilic compound, griseofulvin, was improved by about 30% due to nanonization under non-sink conditions. Moreover, this permeability was about 50% higher than that under sink conditions. On the other hand, for the low lipophilic compound, hydrocortisone, there was no difference in permeability between micro-and nano-sized compounds under non-sink conditions. The nanonization of highly lipophilic compounds improves the permeability of the unstirred water layer (UWL), which in turn improves overall permeability. On the other hand, because the rate-limiting step in permeation for the low lipophilic compounds is the diffusion of the compounds in the membrane, the improvement of UWL permeability by nanonization does not improve the overall permeability. Based on this mechanism, nanoparticle formulations are not effective for low lipophilic compounds. To accurately predict the absorption of nanoparticle formulations, it is necessary to consider their permeability under non-sink conditions which reflect in vivo conditions.

Amorphous Form of Carvedilol Phosphate-The Case of Divergent Properties

The amorphous form of carvedilol phosphate (CVD) was obtained as a result of grinding. The identity of the obtained amorphous form was confirmed by powder X-ray diffraction (PXRD), different scanning calorimetry (DSC), and FT-IR spectroscopy. The process was optimized in order to obtain the appropriate efficiency and time. The crystalline form of CVD was used as the reference standard. Solid dispersions of crystalline and amorphous CVD forms with hydrophilic polymers (hydroxypropyl-β-cyclodextrin, Pluronic^® F-127, and Soluplus^®) were obtained. Their solubility at pH 1.2 and 6.8 was carried out, as well as their permeation through a model system of biological membranes suitable for the gastrointestinal tract (PAMPA-GIT) was established. The influence of selected polymers on CVD properties was defined for the amorphous form regarding the crystalline form of CVD. As a result of grinding (four milling cycles lasting 15 min with 5 min breaks), amorphous CVD was obtained. Its presence was confirmed by the “halo effect” on the diffraction patterns, the disappearance of the peak at 160.5 °C in the thermograms, and the changes in position/disappearance of many characteristic bands on the FT-IR spectra. As a result of changes in the CVD structure, its lower solubility at pH 1.2 and pH 6.8 was noted. While the amorphous dispersions of CVD, especially with Pluronic^® F-127, achieved better solubility than combinations of crystalline forms with excipients. Using the PAMPA-GIT model, amorphous CVD was assessed as high permeable (Papp > 1 × 10⁻⁶ cm/s), similarly with its amorphous dispersions with excipients (hydroxypropyl-β-cyclodextrin, Pluronic^® F-127, and Soluplus^®), although in their cases, the values of apparent constants permeability were decreased.