UNGAP best practice for improving solubility data quality of orally administered drugs

An important goal of the European Cooperation in Science and Technology (COST) Action UNGAP (UNderstanding Gastrointestinal Absorption-related Processes, www.ungap.eu) is to improve standardization of methods relating to the study of oral drug absorption. Solubility is a general term that refers to the maximum achievable concentration of a compound dissolved in a liquid medium. For orally administered drugs, relevant information on drug properties is crucial during drug (product) development and at the regulatory level. Collection of reliable and reproducible solubility data requires careful application and understanding of the limitations of the selected experimental method. In addition, the purity of a compound and its solid state form, as well as experimental parameters such as temperature of experimentation, media related factors, and sample handling procedures can affect data quality. In this paper, an international consensus developed by the COST UNGAP network on recommendations for collecting high quality solubility data for the development of orally administered drugs is proposed.

Molecular salts of quinine: a crystal engineering route to enhance the aqueous solubility

Salts of quinine, with α,ω-aliphatic dicarboxylic acids, and aromatic coformers, show superior aqueous solubility. The structural, thermal and microscopy data provide structural, compositional, and stability profiles of the salts.

Development of olmesartan medoxomil lipid-based nanoparticles and nanosuspension: preparation, characterization and comparative pharmacokinetic evaluation

The aim was to enhance the oral bioavailability of olmesartan medoxomil (OM) by preparing solid lipid nanoparticles (SLNs) and comparing with nanosuspension (OM-NS). OM-SLNs and OM-NS were prepared by known methods. Prepared SLNs were evaluated for physical characters and in vivo pharmacokinetic (PK) performance in rats. OM-NS showed more than four-fold increase in the solubility. During DSC and XRD studies, drug incorporated in SLNs was found to be in amorphous form. The relative bioavailability of OM-SLN and OM-NS was 7.21- and 3.52-fold when compared with that of coarse suspension. Further, OM-SLNs also increased the oral bioavailability by two-fold over that of OM-NS.

Influence of critical parameters of nanosuspension formulation on the permeability of a poorly soluble drug through the skin--a case study

In transdermal drug delivery systems, it is always a challenge to achieve stable and prolonged high permeation rates across the skin since the concentrations of the drug dissolved in the matrix have to be high in order to maintain zero order release kinetics. Several attempts have been reported to improve the permeability of poorly soluble drug compounds using supersaturated systems. However, due to thermodynamic challenges, there was a high tendency for the drug to nucleate immediately after formulating or even during storage. The present study focuses on the efficiency of nanoparticles and influence of different concentrations of solubilizer such as vitamin E TPGS (D-a-tocopheryl polyethylene glycol 1000 succinate) to improve the permeation rate through the skin. Effects of several formulation factors were studied on the nanosuspension systems using ibuprofen as a model drug. The overall permeation enhancement process through the skin was influenced mostly by the solubilizer and also by the size of nanoparticles. The gel formulation developed with vitamin E TPGS + HPMC nanosuspension, consequently represent a promising approach aiming to improve the permeability performance of a poorly water soluble drug candidate.

Green amorphous nanoplex as a new supersaturating drug delivery system

The nanoscale formulation of amorphous drugs represents a highly viable supersaturating drug-delivery system for enhancing the bioavailability of poorly soluble drugs. Herein we present a new formulation of a nanoscale amorphous drug in the form of a drug-polyelectrolyte nanoparticle complex (or nanoplex), where the nanoplex is held together by the combination of a drug-polyelectrolyte electrostatic interaction and an interdrug hydrophobic interaction. The nanoplex is prepared by a truly simple, green process that involves the ambient mixing of drug and polyelectrolyte (PE) solutions in the presence of salt. Nanoplexes of poorly soluble acidic (i.e., ibuprofen and curcumin) and basic (i.e., ciprofloxacin) drugs are successfully prepared using biocompatible poly(allylamine hydrochloride) and dextran sulfate as the PE, respectively. The roles of salt, drug, and PE in nanoplex formation are examined from ternary phase diagrams of the drug-PE complex, from which the importance of the drug's charge density and hydrophobicity, as well as the PE ionization at different pH values, is recognized. Under the optimal conditions, the three nanoplexes exhibit high drug loadings of ~80-85% owing to the high drug complexation efficiency (~90-96%), which is achieved by keeping the feed charge ratio of the drug to PE below unity (i.e., excess PE). The nanoplex sizes are ~300-500 nm depending on the drug hydrophobicity. The nanoplex powders remain amorphous after 1 month of storage, indicating the high stability owed to the PE's high glass-transition temperature. FT-IR analysis shows that functional groups of the drug are conserved upon complexation. The nanoplexes are capable of generating prolonged supersaturation upon dissolution with precipitation inhibitors. The supersaturation level depends on the saturation solubility of the native drugs, where the lower the saturation solubility, the higher the supersaturation level. The solubility of curcumin as the least-soluble drug is magnified 9-fold upon its transformation to the nanoplex, and the supersaturated condition is maintained for 5 h.

Early development evaluation of AZD2738, a substrate for the NK receptors

The purpose of this study was to investigate whether AZD2738, a dual neurokinin NK1/2 receptor antagonist, is a suitable candidate for further development with an oral immediate release solid dosage form as a possible final product. The neutral form of AZD2738 has only been isolated as amorphous material. In order to search for a solid material with improved physical and chemical stability and more suitable solid-state properties, a salt screen was performed. Mostly crystalline material of fumarate, maleate and chloride salt of AZD2738 were obtained. X-ray powder diffractometry, thermogravimetric analysis, differential scanning calorimetry and dynamic vapor sorption were used to investigate the physicochemical characteristics of the salts. Based on the physicochemical properties, the chloride salt is preferred for continued product development. The chloride salt of AZD2738 is an anhydrate, the crystallization is reproducible, the hygroscopicity is acceptable and just one polymorph was obtained. Notably is that the two obtained polymorphs of the fumarate salt of AZD2738 are monotropically related, whereas the two identified polymorphs for the maleate salt of the compound are enantiotropic. The dissolution behavior and the stability (in aqueous solutions, formulations and solid state) of the salts were also studied and found to be satisfactory, at least at pH >3. Liquid formulations should preferable be stored frozen at pH >3.

Physicochemical and pharmacokinetic characterization of a spray-dried cefpodoxime proxetil nanosuspension

Cefpodoxime proxetil (CP) is a prodrug, the third generation cephem-type broad-spectrum antibiotic administered orally. However, CP was found to be a poorly water-soluble drug with low bioavailability when orally administered. In the present investigation, the spray-dried cefpodoxime proxetil nanosuspension (SDN) was prepared. The physicochemical properties were characterized by rheological evaluation, particle size measurement and its distribution, dynamics of reconstitution, in-vitro dissolution testing, surface morphology, surface area and pore size measurements. The pharmacokinetic study of SDN, in comparison to a marketed cefpodoxime proxetil for oral suspension (MS), was also performed in rabbits after a single oral dose. It was found that SDN exhibited a significant decrease in t(max), a 1.60-fold higher area under curve (AUC) and 2.33-fold higher maximum plasma concentration (C(max)) than MS.

Current Perspectives of Solubilization: Potential for Improved Bioavailability

This review focuses on the recent techniques of solubilization for the attainment of effective absorption and improved bioavailability. Solubilization may be affected due to cosolvent water interaction or altered crystal structure by cosolvent addition. Micellar solubilization could be affected by both ionic strength and pH. Addition of cosolvents to the surfactant solutions offers only a small advantage because of the decrease in the solubilization capacity of the micelles. Polymorphism is known to influence dissolution and bioavailability of the drugs. Molecular modeling study of cyclodextrin inclusion complexations can predict the inclusion modes, stoichiometry of the complex, and the relative complexing efficiency of cyclodextrins with various drug molecules.

Impact of the Amount of Excess Solids on Apparent Solubility

PURPOSE

The impact of excess solids on the apparent solubility is examined.

METHODS

The apparent solubility of some model drugs was measured in various buffered solutions, with various amounts of excess solid. To help understand the dependence of the solubility on the amount of solid, we evaluated the dissolution and crystallization rates of indomethacin (IDM), one of the model drugs, at near-equilibrium conditions.

RESULTS

In the case of IDM, the apparent solubility decreased with an increase in the solid amount at pH 5 and 6. On the other hand, it increased with an increase in the solid amount at pH 6.5 and 7. The crystallization and dissolution rates of IDM decreased and increased, respectively, with an increase in pH values, and became equal at between pH 6 and 7. Therefore, the apparent solubility was most likely to be affected by the balance between the crystallization and dissolution rates. The apparent solubility of other model drugs showed the same trend, although the dependency on the solid amount was not as significant as in the case of IDM.

CONCLUSIONS

The apparent solubility was affected by the amount of solid for all the model drugs investigated. This was most likely to be caused by a competition between the crystallization and dissolution rates.

Solid-state variation of troglitazone drug substance by using a different recrystallization method

Rapid and slow crystallization methods (A and B) were applied for troglitazone, an equal mixture of four stereoisomers. Differences in the powder x-ray diffractometry patterns and hygroscopic patterns were observed among the samples crystallized by these methods, suggesting that troglitazone has solid-state variation. In this article, troglitazone recrystallized by method A was evaluated to clarify its structural characteristics and physical property. The crystal structure of predried troglitazone recrystallized by method A was proved to be a dihydrate. By drying, it changed reversibly to an anhydrate, which is the same structure as the RS/SR form, keeping the same enantiomer ratio. The solubility of the troglitazone by method A higher than that by method B at all enantiomer levels. But making the troglitazone amorphous equalized the enantiomeric solubilities of the substances by both methods as well as increased the intrinsic solubilities. Troglitazone by both methods was proved to be stable and retained the ratio of the stereoisomers.

Evaluation of the stability of creatine in solution prepared from effervescent creatine formulations

The objectives of this study were to determine the cause of the crystallization in a large volume creatine supplement solution made from effervescent powders containing di-creatine citrate, and to characterize these crystals using thermal analyses and x-ray diffractometry. Creatine effervescent powders were dissolved in deionized water (pH 6.2) and stored both at room temperature (RT) (25 degrees C) and refrigerated condition (4 degrees C) over a period of 45 days. Creatine concentration was determined using high-performance liquid chromatography (HPLC). Intrinsic dissolution and saturated solubility of creatine, creatine monohydrate, and di-creatine citrate in water were determined and compared. Crystal growth was detected only in the refrigerated samples on the seventh day of storage. Differential Scanning Calorimetry (DSC) and x-ray diffraction (XRD) studies revealed that the crystals formed were of creatine monohydrate. Ninety percent creatine degradation was observed within 45 days for RT samples. However, at refrigerated condition this degradation was 80% within the same time period. The pH of the RT samples also increased from 3.6 to 4.5 during storage. No such increase was observed in the case of refrigerated samples. The intrinsic dissolution rate constants of the compounds decreased in the following order: di-creatine citrate > creatine > creatine monohydrate. In conclusion, di-creatine citrate used in effervescent formulation dissociates to creatine in aqueous solution and eventually crystallizes out as creatine monohydrate. Significant decrease in solubility and effect of pH contribute to this crystallization process.