<P> The metabolic stability and the reactivity of a library of candidate drug compounds have to be assessed for drug metabolism and toxicological studies . Many methods have been proposed for quantitative predictions in drug metabolism; one example of a recent computational method is SPORCalc . If the chemical structure of a medicinal compound is altered slightly, this could slightly or dramatically alter the medicinal properties of the compound depending on the level of alteration as it relates to the structural composition of the substrate or receptor site on which it exerts its medicinal effect, a concept referred to as the structural activity relationship (SAR). This means that when a useful activity has been identified, chemists will make many similar compounds called analogues, in an attempt to maximize the desired medicinal effect (s) of the compound . This development phase can take anywhere from a few years to a decade or more and is very expensive . </P> <P> These new analogues need to be developed . It needs to be determined how safe the medicine is for human consumption, its stability in the human body and the best form for delivery to the desired organ system, like tablet or aerosol . After extensive testing, which can take up to 6 years, the new medicine is ready for marketing and selling . </P> <P> As a result of the long time required to develop analogues and test a new medicine and the fact that of every 5000 potential new medicines typically only one will ever reach the open market, this is an expensive way of doing things, often costing over 1 billion dollars . To recoup this outlay pharmaceutical companies may do a number of things: </P> <Ul> <Li> Carefully research the demand for their potential new product before spending an outlay of company funds . </Li> <Li> Obtain a patent on the new medicine preventing other companies from producing that medicine for a certain allocation of time . </Li> </Ul>

Name the branches of subject pharmacology and toxicology