In vitro-in vivo correlation in the effect of cyclodextrin on oral absorption of poorly soluble drugs

Solubility-enabling formulations for oral delivery of lipophilic drugs: considering the solubility-permeability interplay for accelerated formulation development

INTRODUCTION

Tackling low water solubility of drug candidates is a major challenge in today's pharmaceutics/biopharmaceutics, especially by means of modern solubility-enabling formulations. However, drug absorption from these formulations oftentimes remains unchanged or even decreases, despite substantial solubility enhancement.

AREAS COVERED

In this article, we overview the simultaneous effects of the formulation on the solubility and the apparent permeability of the drug, and analyze the contribution of this solubility-permeability interplay to the success/failure of the formulation to increase the overall absorption and bioavailability. Three different patterns of interplay were identified: (1) solubility-permeability tradeoff in which every solubility gain comes with a price of concomitant permeability loss; (2) an advantageous interplay pattern in which the permeability remains unchanged alongside the solubility gain; and (3) an optimal interplay pattern in which the formulation increases both the solubility and the permeability. Passive vs. active intestinal permeability considerations in the context of the solubility-permeability interplay are also thoroughly discussed.

EXPERT OPINION

The solubility-permeability interplay pattern of a given formulation has a critical effect on its overall success/failure, and hence, taking into account both parameters in solubility-enabling formulation development is prudent and highly recommended.

Leveraging the use of in vitro and computational methods to support the development of enabling oral drug products: An InPharma commentary

Due to the strong tendency towards poorly soluble drugs in modern development pipelines, enabling drug formulations such as amorphous solid dispersions, cyclodextrins, co-crystals and lipid-based formulations are frequently applied to solubilize or generate supersaturation in gastrointestinal fluids, thus enhancing oral drug absorption. Although many innovative in vitro and in silico tools have been introduced in recent years to aid development of enabling formulations, significant knowledge gaps still exist with respect to how best to implement them. As a result, the development strategy for enabling formulations varies considerably within the industry and many elements of empiricism remain. The InPharma network aims to advance a mechanistic, animal-free approach to the assessment of drug developability. This commentary focuses current status and next steps that will be taken in InPharma to identify and fully utilize 'best practice' in vitro and in silico tools for use in physiologically based biopharmaceutic models.

Anomalous Properties of Cyclodextrins and Their Complexes in Aqueous Solutions

Cyclodextrins (CDs) are cyclic oligosaccharides that emerged as industrial excipients in the early 1970s and are currently found in at least 130 marketed pharmaceutical products, in addition to numerous other consumer products. Although CDs have been the subject of close to 100,000 publications since their discovery, and although their structure and properties appear to be trivial, CDs are constantly surprising investigators by their unique physicochemical properties. In aqueous solutions, CDs are solubilizing complexing agents of poorly soluble drugs while they can also act as organic cosolvents like ethanol. CDs and their complexes self-assemble in aqueous solutions to form both nano- and microparticles. The nanoparticles have diameters that are well below the wavelength of visible light; thus, the solutions appear to be clear. However, the nanoparticles can result in erroneous conclusions and misinterpretations of experimental results. CDs can act as penetration enhancers, increasing drug permeation through lipophilic membranes, but they do so without affecting the membrane barrier. This review is an account of some of the unexpected results the authors have encountered during their studies of CDs as pharmaceutical excipients.

β-cyclodextrin microencapsulation enhanced antioxidant and antihyperlipidemic properties of Tunisian Periploca angustifolia roots condensed tannins in rats

This study aimed to investigate the microencapsulation of novel condensed tannins isolated from Periploca angustifolia roots, using β-cyclodextrin macrocyclic oligosaccharides, in order to enhance their antioxidant and antihyperlipidemic potentials. Scanning electron microscopy and Fourier transform infrared spectroscopy results revealed that tannin fraction was successfully included into β-cyclodextrin cavities proved with an encapsulation efficacy of 70%. Our in vitro findings highlighted that both pure and encapsulated tannins have efficient inhibition capacities of pancreatic lipase activity. However, the inclusion complex has the greatest, in vivo, antioxidant, and antihyperlipidemic effects. In fact, results showed that complexed tannins had markedly restored serum lipid biomarkers, lipid peroxidation, protein carbonyl oxidation, and antioxidant enzyme defense. These findings were additionally confirmed by aortic and myocardial muscle sections of histological examination. Consequently, β-cyclodextrin microencapsulation may be considered as an effective and promising technique for tannin delivery with improved antioxidant and antihyperlipidemic activities.

Form quantitation in desmotropic mixtures of albendazole bulk drug by chemometrics-assisted analysis of vibrational spectra

Albendazole is a benzimidazole-type active pharmaceutical ingredient, and one of the most effective broad-spectrum anthelminthic agents. The drug has two solid-state forms (ALB I and ALB II) which are desmotropes; both of them seem to be currently marketed. However, using the wrong crystalline solid form for formulation may have an undesired impact on the physicochemical and/or bioavailability properties of the drug product. In order to develop new, simple, and less expensive alternatives toward the determination of the level of albendazole ALB I in its mixtures with ALB II, both desmotropes were prepared, and properly characterized by spectroscopic [solid-state nuclear magnetic resonance and near infrared (NIR)] and diffractometric (powder X-ray diffraction) methods. Then, the NIR and attenuated total reflectance-mid infrared (ATR-MIR) spectra of both forms were conveniently pre-treated and employed for the development and optimization of partial least squares (PLS)-potentiated quantification models (NIR/PLS and ATR-MIR/PLS). The latter were also subjected to validation (accuracy, precision, limits of detection and quantification, etc.) and further used to assess the level of the unwanted ALB II form in the bulk drug. The NIR/PLS method displayed the most satisfactory characteristics, including a limit of quantitation interval of 3.6 ± 1 %w/w; it outperformed both, the ATR-MIR/PLS counterpart (limit of quantitation interval of 14.0 ± 3.4 %w/w) and a previously published and more demanding Raman/PLS alternative.

Fast dissolving nanofiber mat for the local antimicrobial application of roxithromycin in oral cavity

Fast disintegrating and dissolving nanofiber (NF) mat was devised to deliver roxithromycin for the treatment of the respiratory tract infection. NF membrane was made by an electrospinning process with poly(vinyl alcohol) (PVA), hydroxypropyl-β-cyclodextrin (HP-β-CD), and d-α-tocopheryl polyethylene glycol succinate (TPGS) for local application of roxithromycin. Roxithromycin has a poor water solubility thus HP-β-CD is introduced for enhancing drug solubility by forming an inclusion complex in this study. The addition of TPGS provided multiple roles such as accelerating wetting, disintegration, and dissolution speed and overcoming bacterial resistance. Roxithromycin was successfully entrapped in NF structure and drug amorphization occurred during the electrospinning process. PVA/HP-β-CD/TPGS/roxithromycin (PHTR) NF exhibited faster wetting, disintegration, and dissolution speed rather than the other NF mats. PHTR NF displayed higher antibacterial potentials in Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus) compared to other NF mat formulations. The administration of PHTR NF to oral cavity in pneumococcal disease mouse model provided the most efficient therapeutic potentials in lung tissue. Designed multiple phase-based NF mat may be one of powerful local drug delivery systems for the therapy of respiratory tract infection.

Dissolution/Permeation of Albendazole in the Presence of Cyclodextrin and Bile Salts: A Mechanistic In-Vitro Study into Factors Governing Oral Bioavailability

We aimed to understand the impact of the interplay between bile salts and cyclodextrins on the dissolution-permeation of poorly soluble drug compounds with a moderate-strong binding constant to cyclodextrin. Phase diagrams were prepared on the chosen model compound albendazole in phosphate buffer, fasted state simulated intestinal fluid (FaSSIF), and a modified fed state simulated intestinal fluid (FeSSIF_mod) with (2-hydroxypropyl)-beta-cyclodextrin (HP-β-CD) concentrations of up to 10 % (m/m). Then we investigated the dissolution/permeation interplay of albendazole dissolved/suspended in the different media through a biomimetic barrier on a 96-well in vitro model. The apparent solubility of albendazole was enhanced by HP-β-CD and FaSSIF/FeSSIF_mod separately. However, when albendazole was dissolved in HP-β-CD and biomimetic media together, the solubility was significantly lower than the predicted additive solubility from the solubilizing effects. It is postulated that this is due to the sodium taurocholate from the biomimetic media displacing albendazole from the hydrophobic cavity of HP-β-CD. In the permeation experiments, the highest permeation was observed at cyclodextrin concentrations able to solubilize close to the total dose of albendazole without a major surplus of solubilization capacity. Furthermore, an over-proportional permeation enhancement was observed when both, cyclodextrin and biomimetic media were present. These results indicate that the interplay between bile salts and cyclodextrins can enhance the free (molecularly dissolved) fraction of drug in solution to a greater extent than could be obtained with one of the solubilizing components alone. In conclusion, at carefully selected cyclodextrin-concentrations in combination with biomimetic media, obviously, a transient supersaturation is induced, which is made responsible for the observed major permeation enhancement.

Rational formulation engineering of fraxinellone utilizing 6-O-α-D-maltosyl-β-cyclodextrin for enhanced oral bioavailability and hepatic fibrosis therapy

Although Fraxinellone (Frax) isolated from Dictamnus albus L. possessed excellent anti-hepatic fibrosis activity, oral administration of Frax suffered from the inefficient therapeutic outcome in vivo due to negligible oral absorption. At present, the oral formulation of Frax is rarely exploited. For rational formulation design, we evaluated preabsorption risks of Frax and found that Frax was rather stable while poorly dissolved in the gastrointestinal tract (78.88 μg/mL), which predominantly limited its oral absorption. Further solubility test revealed the outstanding capacity of cyclodextrin derivatives (CDs) to solubilize Frax (6.8-12.8 mg/mL). This led us to study the inclusion complexes of Frax with a series of CDs and holistically explore their drug delivery performance. Characterization techniques involving ¹H-NMR, FT-IR, DSC, PXRD, and molecular docking confirmed the most stable binding interactions when Frax complexed with 6-O-α-D-maltosyl-β-cyclodextrin (G₂-β-CD-Frax). Notably, G₂-β-CD-Frax exhibited the highest solubilizing capacity, fast dissolution rate, and superior Caco-2 cell internalization with no obvious toxicity. Pharmacokinetic studies demonstrated markedly higher oral bioavailability of G₂-β-CD-Frax (5.8-fold that of free drug) than other Frax-CDs. Further, long-term administration of G₂-β-CD-Frax (5 mg/kg) efficiently inhibited CCl₄-induced hepatic fibrosis in the mouse without inducing any toxicity. Our results will inspire the continued advancement of optimal oral Frax formulations for anti-fibrotic therapy.