Solid Carriers for Improved Solubility of Glipizide in Osmotically Controlled Oral Drug Delivery System

Formulation and characterization of glipizide solid dosage form with enhanced solubility

Glipizide, a poor water-soluble drug belongs to BCS class II. The proposed work aimed to enhance the solubility of glipizide by preparing solid dispersions, using polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG). Solvent evaporation method was used for the preparation of glipizide solid dispersions. Solid dispersions were prepared in four different drug-to-polymer ratios i.e. 1:1, 1:2, 1:3 and 1:4. Mainly effect of three polymers (PVP K30, PVP K90 and PEG 6000) was evaluated on the solubility and dissolution of glipizide. The in-vitro dissolution of all prepared formulations was performed under pH 6.8 at 37°C using USP type II apparatus. In-vitro dissolution results revealed that the formulations having high concentrations of the polymer showed enhanced solubility. Enhancements in the solubility and rate of dissolution of the drug were noted in solid dispersion formulations compared to the physical blends and pure drug. Solid dispersions containing polyvinyl pyrrolidone exhibited a more favorable pattern of drug release compared to the corresponding solid dispersions with PEG. An increase in the maximum solubility of the drug within the solid dispersion systems was observed in all instances. Two solid dispersion formulations were optimized and formulated into immediate-release tablets, which passed all the pharmacopoeial and non-pharmacopoeial tests. Fourier transformed Infrared (FTIR) spectroscopy X-ray diffraction (XRD) and Differential scanning calorimetry (DSC) were used to indicate drug: polymer interactions in solid state. Analysis of the solid dispersion samples through characterization tests indicated the compatibility between the drug and the polymer.

Solubility Measurement and Various Solubility Parameters of Glipizide in Different Neat Solvents

Glipizide (GLZ) is an oral hypoglycemic agent, which is a weakly aqueous soluble drug. The solubility values of GLZ in various neat solvents are scarce in the literature. Hence, the solubility of GLZ in 12 different neat solvents, namely, "water, methanol, ethanol, isopropanol (IPA), 1-butanol, 2-butanol, ethylene glycol (EG), propylene glycol (PG), poly(ethylene glycol)-400 (PEG-400), ethyl acetate (EA), dimethyl sulfoxide (DMSO), and Transcutol-HP (THP)", at "T = 298.2-318.2 K" and "p = 0.1 MPa" was measured. The recorded solubilities of GLZ were correlated by "van't Hoff and Apelblat models" using root-mean-square deviation (RMSD). The overall RMSD was obtained as 1.21 and 1.40% for "Apelblat and van't Hoff models", respectively. Different solubility parameters of all studied materials including drug and solvent were calculated to find the best solvent for GLZ. The solubilities of GLZ (expressed in mole fraction) have been found highest in DMSO (2.81 × 10^-2), followed by THP, EA, 2-butanol, 1-butanol, IPA, PEG-400, ethanol, PG, methanol, EG, and water (1.98 × 10^-4) at "T = 318.2 K". All investigated solubility parameters of GLZ were recorded very close to the DMSO. "Apparent thermodynamic analysis" showed an "endothermic and entropy-driven dissolution" of GLZ in the 12 different neat solvents. The highest molecular interactions were recorded in GLZ-DMSO compared to other combinations. Overall, DMSO has been considered as the best solvent for the solubilization of GLZ.

Decision trees to characterise the roles of permeability and solubility on the prediction of oral absorption

Oral absorption of compounds depends on many physiological, physiochemical and formulation factors. Two important properties that govern oral absorption are in vitro permeability and solubility, which are commonly used as indicators of human intestinal absorption. Despite this, the nature and exact characteristics of the relationship between these parameters are not well understood. In this study a large dataset of human intestinal absorption was collated along with in vitro permeability, aqueous solubility, melting point, and maximum dose for the same compounds. The dataset allowed a permeability threshold to be established objectively to predict high or low intestinal absorption. Using this permeability threshold, classification decision trees incorporating a solubility-related parameter such as experimental or predicted solubility, or the melting point based absorption potential (MPbAP), along with structural molecular descriptors were developed and validated to predict oral absorption class. The decision trees were able to determine the individual roles of permeability and solubility in oral absorption process. Poorly permeable compounds with high solubility show low intestinal absorption, whereas poorly water soluble compounds with high or low permeability may have high intestinal absorption provided that they have certain molecular characteristics such as a small polar surface or specific topology.

Impact of polymers on dissolution performance of an amorphous gelleable drug from surface-coated beads

A non-ionic amorphous active API ((RR)-3((1R)-3-oxocyclopentyl)-2-[3-chloro-4-methyl sulfonyl]phenyl-N-pyrozin-2ylpropanamide) with a glass transition temperature of 60 degrees C and aqueous solubility of 0.8 mg/mL was layered on the cellulose beads by the help of an anionic (Eudragit L100) and a non-ionic (polyvinylpyrrolidone) PVP K30 polymer respectively. An "immediate" and complete release of API from the anionic (Eudragit L100), and "sustained" but incomplete release from the hygroscopic non-ionic polymer coatings were observed. The effect of the PVP K30, and delivery patterns were investigated. Water uptake of the polymers and flow properties of API upon exposure to humidity as well as moisture sorption of beadlets were determined. Drug-polymer interactions and coating morphologies that were examined via near infrared imaging (NIR), microscopy and FTIR, enlightened any possible drug-polymer interaction. From the anionic polymer coating 93.5% API was dissolved in 50 min whereas the non-ionic polymer coating released 60% drug within 5 h. There were no API-polymer interactions as demonstrated by FTIR, implying that, this factor did not play any role in the differences observed in the release profiles. However, gelling, clumping and agglomeration was observed on the surface of the particles coated with PVP which resulted in slow and incomplete release of the drug. The anionic polymer protected API, by preventing its gelling and clumping in situ while the non-ionic polymer promoted gelling. Because API gels at a critical moisture level and at an associated critical time interval, any delivery system that can protect the drug from reaching to the critical moisture level can control API release. The drug was released via surface erosion from the Eudragit L100 coating, whereas PVP K30, the non-ionic polymer, released API via diffusion process. The results indicate that polymer properties can play a critical role in the release mechanism and kinetics of gelleable drugs. The anionic polymers may protect drugs of similar nature from gelling when exposed to the dissolution media. An understanding of mechanisms involved in drug-polymer interactions will be useful to screen the polymers that are useful in engineering suitable delivery systems for such drugs.