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.

Approaches to increase mechanistic understanding and aid in the selection of precipitation inhibitors for supersaturating formulations – a PEARRL review

Objectives

Supersaturating formulations hold great promise for delivery of poorly soluble active pharmaceutical ingredients (APIs). To profit from supersaturating formulations, precipitation is hindered with precipitation inhibitors (PIs), maintaining drug concentrations for as long as possible. This review provides a brief overview of supersaturation and precipitation, focusing on precipitation inhibition. Trial-and-error PI selection will be examined alongside established PI screening techniques. Primarily, however, this review will focus on recent advances that utilise advanced analytical techniques to increase mechanistic understanding of PI action and systematic PI selection.

Key findings

Advances in mechanistic understanding have been made possible by the use of analytical tools such as spectroscopy, microscopy and mathematical and molecular modelling, which have been reviewed herein. Using these techniques, PI selection can be guided by molecular rationale. However, more work is required to see widespread application of such an approach for PI selection.

Summary

Precipitation inhibitors are becoming increasingly important in enabling formulations. Trial-and-error approaches have seen success thus far. However, it is essential to learn more about the mode of action of PIs if the most optimal formulations are to be realised. Robust analytical tools, and the knowledge of where and how they can be applied, will be essential in this endeavour.

Bile salts and their importance for drug absorption

Bile salts are present in the intestines of humans as well as the animals used during the development of pharmaceutical products. This review provides a short introduction into the physical chemical properties of bile salts, a description of the bile concentration and composition of bile in different animal species and an overview of the literature investigating the influence of bile salts on the in vivo performance of different compounds and drug formulations. Generally, there is a positive effect on bioavailability when bile is present in the gastro-intestinal tract, independent of the formulation systems, e.g. suspensions, solutions, cyclodextrin complexes or lipid based formulations, but a few exceptions have also been reported.

Oral bioavailability of a poorly aqueous drug from three different SBE7-β-cyclodextrin based formulations in beagle dogs

Oral administration of Lu 35-138, a low aqueous soluble compound, was investigated in three different formulations containing sulfobutylether β-cyclodextrin (SBE7βCD) in fasted beagle dogs. The evaluated formulations was (i) a SBE7βCD solution, (ii) a spray dried solution filled into hard gelatine capsules, and (iii) a direct compressible tablet containing SBE7βCD. The three formulations did not lead any significant differences in the obtained AUCs, though a trend was observed for the highest absorption when Lu 35-138 was dosed in the cyclodextrin solution. These results demonstrate that a solid formulation with a relative low content of cyclodextrins can be used to increase the bioavailability of a low water soluble compound to a relative high level when compared to a cyclodextrin solution.

Pharmaceutical applications of cyclodextrins: basic science and product development

Objectives

Drug pipelines are becoming increasingly difficult to formulate. This is punctuated by both retrospective and prospective analyses that show that while 40% of currently marketed drugs are poorly soluble based on the definition of the biopharmaceutical classification system (BCS), about 90% of drugs in development can be characterized as poorly soluble. Although a number of techniques have been suggested for increasing oral bioavailability and for enabling parenteral formulations, cyclodextrins have emerged as a productive approach. This short review is intended to provide both some basic science information as well as data on the ability to develop drugs in cyclodextrin-containing formulations.

Key findings

There are currently a number of marketed products that make use of these functional solubilizing excipients and new product introduction continues to demonstrate their high added value. The ability to predict whether cyclodextrins will be of benefit in creating a dosage form for a particular drug candidate requires a good working knowledge of the properties of cyclodextrins, their mechanism of solubilization and factors that contribute to, or detract from, the biopharmaceutical characteristics of the formed complexes.

Summary

We provide basic science information as well as data on the development of drugs in cyclodextrin-containing formulations. Cyclodextrins have emerged as an important tool in the formulator's armamentarium to improve apparent solubility and dissolution rate for poorly water-soluble drug candidates. The continued interest and productivity of these materials bode well for future application and their currency as excipients in research, development and drug product marketing.

The effects of pharmaceutical excipients on drug disposition

Many new chemical entities are poorly soluble, requiring the use of co-solvents or excipients to produce suitable intravenous formulations for early pre-clinical development studies. There is some evidence in the literature that these formulation components can have significant physiological and physicochemical effects which may alter the distribution and elimination of co-administered drugs. Such effects have the potential to influence the results of pre-clinical pharmacokinetic studies, giving a false impression of a compound's intrinsic pharmacokinetics and frustrating attempts to predict the drug's ultimate clinical pharmacokinetics. This review describes the reported effects of commonly used co-solvents and excipients on drug pharmacokinetics and on physiological systems which are likely to influence drug disposition. Such information will be useful in study design and evaluating data from pharmacokinetic experiments, so that the potential influence of formulation components can be minimised.

Complexation of tauro- and glyco-conjugated bile salts with three neutral β-CDs studied by ACE

Complexation of the bile salts (BS) taurocholate, tauro-beta-muricholate, taurodeoxycholate, taurochenodeoxycholate, glycocholate, glycodeoxycholate, and glycochenodeoxycholate common in rat, dog, and man with natural beta-CD and the chemically modified beta-CDs 2-hydroxypropyl-beta-CD and 2-O-methyl-beta-CD was studied using mobility shift ACE. The CDs were selected due to their frequent use in preformulation and drug formulation as oral excipients for the solubilization of drug substances with low aqueous solubility. ACE was demonstrated to be a feasible and efficient technique for investigation of the interactions between BS and beta-CDs. All the investigated BS possessed affinity for the three CDs with stability constants ranging from 2x10(3) to 4x10(5) M(-) (1). The requirements and assumptions related to the use of ACE for estimating high affinity stability constants were discussed. The extent and pattern of hydroxylation significantly influenced the affinity of the glyco- and tauro-conjugated BS toward the beta-CDs (chenodeoxycholates >> deoxycholates > cholates) whereas the nature of the beta-CD derivatization and BS conjugation played a minor role only. The results indicate that displacement of drug substances from beta-CD inclusion complexes is likely to occur in the small intestine where BS are present potentially influencing drug bioavailability.

Strategies to improve oral drug bioavailability

Efforts to improve oral drug bioavailability have grown in parallel with the pharmaceutical industry. As the number and chemical diversity of drugs has increased, new strategies have been required to develop orally active therapeutics. The past two decades have been characterised by an increased understanding of the causes of low bioavailability and a great deal of innovation in oral drug delivery technologies, marked by an unprecedented growth of the drug delivery industry. The advent of biotechnology and consequent proliferation of biopharmaceuticals have brought new challenges to the drug delivery field. In spite of the difficulties associated with developing oral forms of this type of therapeutics, significant progress has been made in the past few years, with some oral proteins, peptides and other macromolecules currently advancing through clinical trials. This article reviews the approaches that have been successfully applied to improve oral drug bioavailability, primarily, prodrug strategies, lead optimisation through medicinal chemistry and formulation design. Specific strategies to improve the oral bioavailability of biopharmaceuticals are also discussed.