Historically, most drugs were derived from natural sources such as plants. More recently, drugs have been manufactured synthetically, based on our increased knowledge of the function of chemicals in the human body. The newest development in pharmacology is the use of biotechnology to produce drugs. With biotechnology, genes that produce human proteins can be put into another living cell such as bacteria or yeast, and stimulated to produce more of the human protein. In order for drugs be effective, they must reach their intended target site.
Eye drops and ointments are examples of topical drugs.
In most cases, however, drugs must be carried to the target site by the bloodstream. Oral medications are absorbed by the bloodstream from the stomach and intestines and carried to the target site. Drugs administered by these methods eventually reach the bloodstream which carries them to the target site. Parenteral Although oral administration of drugs is generally preferred, many drugs cannot be given orally. Some are not made in oral form.