In vitro dissolution study should ideally be designed to predict in vivo performance precisely, providing key information on the bioavailability and establishing IVIVC. Development of discriminatory in vivo predictive dissolution model and the establishment of IVIVC is difficult to achieve with BCS Class 2 drugs as they exhibit variable absorption along the GI tract owing to pH-dependent solubility, especially for Classes IIa and IIb. In this context, the biphasic dissolution model is a powerful technique for investigating the interplay between dissolution, precipitation and partitioning of various poorly soluble molecules. The dissolution test medium comprising of immiscible aqueous and organic phases enables maintenance of sink conditions and easy quantification of poorly soluble drug partitioning into the organic phase. In the review, novel efforts have been taken to provide comprehensive information on challenges associated with the establishment of IVIVC for BCS Class II drugs, various approaches being adopted for developing discriminatory in vivo predictive dissolution model, significant outcomes of studies on biphasic dissolution model to predict the in vivo dissolution behaviour of BCS Class II drugs and the problems with the use of biphasic dissolution model including the status of FDA on the same.

Recent advances in the field of conversion of solid dispersions of poorly water-soluble drugs in a wide range of hydrophilic or water-soluble carriers into solid dispersion tablets have shown great promise in improving solubility, dissolution rate and oral bioavailability of such drugs. Moreover, proper choice of tablet excipients during tableting of optimised solid dispersions can produce either fast/rapid or sustained drug release profile. Release kinetics have been found to follow either first-order kinetics or Higuchi model and release profiles in most of the cases have been found to be superior to that of conventional tablets or capsules. The present review aims to sum up the various studies on solid dispersion tablets and establish the novelty of this unique approach in the overall improvement of oral bioavailability of poorly water-soluble drugs in a simple and cost-effective manner.

Pulmonary dosage forms constitute an important route of drug delivery for systemic absorption of drugs in management of respiratory diseases as well as diseases such as diabetes, migraine, osteoporosis, and cancer. Performance of different pulmonary dosage forms is greatly influenced by aerodynamic particle size distribution of inhalable particles, spray pattern, fraction of dose actually deposited on pulmonary epithelium, dissolution of active pharmaceutical ingredient and ultimately absorption across pulmonary barriers. In vitro dissolution study should be designed to predict in vivo performance precisely, providing key information on bioavailability and establishing in vitro-in vivo correlation. To obtain meaningful data from dissolution study, focus should be on composition of dissolution medium, dissolution conditions and dissolution test apparatus. For pulmonary dosage forms, selection of physiologically relevant dissolution medium, mimicking lung fluid (LF) is a challenging task. Attempts are being made to develop bio-relevant dissolution medium to overcome the limitations associated with use of conventional media lacking lung surfactant proteins, or several salts normally present in pleural fluid. Use of simulated LFs can give a better understanding of the release mechanisms and possible in vivo behavior of pulmonary dosage forms thereby enhancing the predictive capability of the dissolution testing. In the review, efforts have been taken to provide comprehensive information on composition, physicochemical characteristics and functions of physiological LF, challenges associated with the design and development of dissolution study protocol for pulmonary dosage forms, criteria for selection of an appropriate bio-relevant dissolution medium, comparative study on various reported bio-relevant dissolution media and dissolution apparatuses employed for in vitro characterization of performance of pulmonary dosage forms.