ISBN : 978-93-85073-24-3 1. Rate of dissolution 2. Rate of drug permeation through the biomembrane. To assist successful oral drug development, in vitro dissolution testing has emerged as a preferred method to evaluate development potential of new APIs and drug formulations are shown in Fig 1.4. Fig 1.4: Roles of in-vitro dissolution testing in pharmaceutical drug development The Nernst-Brunner and Levich modification of the Noyes-Whitney equation (eq.1) identified the important factors to the kinetics of in-vivo drug dissolution. These factors include drug diffusivity and solubility in the GI contents, the surface area of the solid wetted by the luminal fluids and the GI hydrodynamics [122]. ------------------ 1 Where dC/dt is the dissolution rate, A is the surface area available for dissolution, D is the diffusion coefficient of the drug, Cs is the saturation solubility of the drug in the dissolution medium, C is the concentration of drug in the medium at time (t) and h is the thickness of the diffusion boundary layer adjacent to the surface of dissolving drug. Several physicochemical and physiological aspects can have a great influence on the factors in eq. (1) and therefore on the dissolution rate, such as crystalline form, 10
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