This approach aims at designing drugs which specifically and selectively fit into the critical sites of the target molecules thereby inactivating the latter. The target molecule may be an enzyme concerned with either metabolism of DNA replication or hormone Receptor or some other important molecule involved in a disease. A successful example of Drug designing is provided by the drug proprandolol used for the treatment of heart attacks and hypertension was awarded J. Black the Nobel prize for physiology and Medicine in 1988 for this work Heart ailment are mainly due to an excess of the hormones norepineophrine and epinephrine, which act through two receptors called B propanolol blocks the B receptor thereby interfering with the action of these hormones.
Another drug called eimetidine blocks the H2 receptor in stomach lining of histamine histamine induces the release of HCl is stomach leading to the development of stomach ulcers. Cimetidine therefore, spacifically cures peptic ulcers by blocking the concerned receptor G Elison and G. Hitchings have used this approach to the useful drugs for the treatment of cancer gout, malaria and viral infections like herpes. Recently drug called azidohymidine has been developed for the treatment of AIDS this drug selectively inhibits the reverse transcriptase of HIV.
Another drug Ro-31-8959 designed to inhibit the HIV protease in stage 3 clinical trials using oral delivery inhibition of protease results in the production of immature non infections viral particles.