PHARMACOLOGY

 COMPARATIVE  BIOAVAILABILITY AND BIOEQUIVALENCE ::

The measurement of plasma concentrations has been the most usual method used for comparative bioavailability studies For the purpose of comparing formulaitons for a drug plasma concentrations/time -curves are constructed for equivalent doses of the sample and for a standard preparation The tests are carried out in normal healthy subjects and with randomised crossover designs if the plasma concentration /time -curve of the test formulation is essentially the same as that of the standard the two products are said to be bioequivalent and the clinical effect of the two products can be expected to be the same The availability of a drug from a formulation when compared with the standard can be expressed as a percentage 

                    Area under curve for the test formulation 

                    -------------------------------------------------- *100

                    Area under curve for the standard 

    The investigation of bioequivalence by means of determination of concentration in biological fluids presents difficulties because it is time consumig it requires the use of human subjects it is affected by number of variables and it cannot be applied for routine testing it would be desirable to have a test in-vitro Dissolution tests can provide a means of comparing a new formulation with one that is known to be therapeutically effective The test can also be used to monitor commercial produciton of an established product