ABSTRACT
Drugs come from many and various sources. They include plant and animal extracts, antibiotics from micro-organisms and an assortment of synthetic chemical compounds. A significant advance in drug research was the discovery of organ extracts. The lives of millions of diabetic patients were saved following the isolation of insulin in 1921. Most new drugs are modelled on existing prototype drugs, natural products or hormones. A chemical compound is produced and tested on animals; structural changes are then made to the molecule to influence the biological activity until the desired effects are seen. In the 20th century, people have come to expect and demand safety and an almost complete, lack of toxicity for the ever-increasing variety of drugs they consume. Whilst animal toxicity tests are being conducted, many other activities take place which are also important for the drug development process. The development of animal models has done much to improve the understanding of disease process as well as treatment.
