Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Strategies to Address Low Drug Solubility in Discovery and Development

Interest in hot-melt extrusion techniques for pharmaceutical applications is growing rapidly with well over 100 papers published in the pharmaceutical scientific literature in the last 12 years. Hot-melt extrusion (HME) has been a widely applied technique in the plastics industry and has been demonstrated recently to be a viable method to prepare several types of dosage forms and drug delivery systems. Hot-melt extruded dosage forms are complex mixtures of active medicaments, functional excipients, and processing aids. HME also offers several advantages over traditional pharmaceutical processing techniques including the absence of solvents, few processing steps, continuous operation, and the possibility of the formation of solid dispersions and improved bioavailability. This article, Part I, reviews the pharmaceutical applications of hot-melt extrusion, including equipment, principles of operation, and process technology. The raw materials processed using this technique are also detailed and the physicochemical properties of the resultant dosage forms are described. Part II of this review will focus on various applications of HME in drug delivery such as granules, pellets, immediate and modified release tablets, transmucosal and transdermal systems, and implants.

Pharmaceutical Applications of Hot-Melt Extrusion: Part I

Pectin-based systems for colon-specific drug delivery via oral route

The present invention relates to modulators of ATP-Binding Cassette (“ABC”) transporters or fragments thereof, including Cystic Fibrosis Transmembrane Conductance Regulator, compositions thereof, and methods therewith. The present invention also relates to methods of treating ABC transporter mediated diseases using such modulators.

Modulators of atp-binding cassette transporters

The use of polysaccharides to target drugs to the colon

Physicochemical properties and mechanism of drug release from ethyl cellulose matrix tablets prepared by direct compression and hot-melt extrusion.

The utility of hypromellose acetate succinate (HPMCAS), a cellulosic enteric coating agent, as a carrier in a solid dispersion of nifedipine (NP) was evaluated in comparison with other polymers, including hypromellose (HPMC), hypromellose phthalate (HPMCP), methacrylic acid ethyl acrylate copolymer (MAEA), and povidone (PVP). An X-ray diffraction study showed that the minimum amount of HPMCAS required to make the drug completely amorphous was the same as that of other cellulosic polymers, and less than that in dispersions using non-cellulosic polymers. Hypromellose acetate succinate showed the highest drug dissolution level from its solid dispersion in a dissolution study using a buffer of pH 6.8. This characteristic was unchanged after a storage test at high temperature and high humidity. The inhibitory effect of HPMCAS on recrystallization of NP from a supersaturated solution was the greatest among all the polymers examined. Further, the drug release pattern could be modulated by altering the ratio of succinoyl and acetyl moieties in the polymer chain. Our results indicate that HPMCAS is an attractive candidate for use as a carrier in solid dispersions.

Evaluation of hypromellose acetate succinate (HPMCAS) as a carrier in solid dispersions.

Dry coating: an innovative enteric coating method using a cellulose derivative.

Supersaturation, nucleation, and crystal growth during single- and biphasic dissolution of amorphous solid dispersions: Polymer effects and implications for oral bioavailability enhancement of poorly water soluble drugs

Sakae Obara

Papers

Physicochemical properties and mechanism of drug release from ethyl cellulose matrix tablets prepared by direct compression and hot-melt extrusion.

Evaluation of hypromellose acetate succinate (HPMCAS) as a carrier in solid dispersions.

Dry coating: an innovative enteric coating method using a cellulose derivative.

Supersaturation, nucleation, and crystal growth during single- and biphasic dissolution of amorphous solid dispersions: Polymer effects and implications for oral bioavailability enhancement of poorly water soluble drugs

Stability assessment of hypromellose acetate succinate (HPMCAS) NF for application in hot melt extrusion (HME).