ISBN : 978-93-85073-24-3 Fig 1.3: Comprehensive Medicinal Chemistry database shows that, of more than 7000 small-molecule drugs, only 5% treat the CNS, and these drugs only treat four disorders: depression, schizophrenia, chronic pain, and epilepsy. There are few effective small or large molecule drugs for the majority of CNS disorders, with the exception of Parkinson’s disease, e.g., L-DOPA, and multiple sclerosis, e.g., cytokines. Solubility and Dissolution The term ‘solubility’ is defined as maximum amount of solute that can be dissolved in a given amount of solvent. It can also be defined quantitatively as well as qualitatively. Quantitatively it is defined as the concentration of the solute in a saturated solution at a certain temperature. In qualitative terms, solubility may be defined as the spontaneous interaction of two or more substances to form a homogenous molecular dispersion. A saturated solution is one in which the solute is in equilibrium with the solvent [118-120]. The solubility behavior of drugs remains one of the most challenging aspects in formulation development. The events that occur following oral administration of a solid dosage form. It is a well formulated dosage form; the two critical rate determining steps in the absorption of orally administered drugs are [121]: 9
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