Identification of biowaivers among Class II drugs: theoretical justification and practical examples

To set up a theoretical basis for identifying biowaivers among Class II drugs and apply the methodology developed to nonsteroidal anti-inflammatory drugs (NSAIDs). The dynamics of the two consecutive drug processes dissolution and wall permeation are considered in the time domain of the physiologic transit time using a tube model of the intestinal lumen. The model considers constant permeability along the intestines, a plug flow fluid with the suspended particles moving with the fluid, and dissolution in the small particle limit. The fundamental differential equation of drug dissolution-uptake in the intestines is expressed in terms of the fraction of dose dissolved. The fundamental parameters, which define oral drug absorption in humans resulting from this analysis, are i) the formulation-related factors, dose, particle radius size, and ii) the drug-related properties, dimensionless solubility/dose ratio (1/q), and effective permeability. Plots of dose as a function of (1/q) for various particle sizes unveil the specific values of these meaningful parameters, which ensure complete absorption for Class II drugs [(1/q) < 1]. A set of NSAIDs were used to illustrate the application of the approach in identifying biowaivers among the NSAIDs. The underlying reason for a region of fully absorbed drugs in Class II originates from the dynamic character of the dissolution-uptake processes. The dynamic character of the approach developed allows identification of biowaivers among Class II drugs. Several biowaivers among the NSAIDs were identified using solubility data at pH 5.0 and in fed-state-simulated intestinal fluid at pH 5.0. The relationships of formulation parameters, dose, particle radius, and the drug properties, dimensionless solubility/dose ratio (1/q), and permeability with the fraction of dose absorbed for drugs with low 1/q values [(1/q) < 1] can be used as guidance for the formulation scientist in the development phase.