THE HISTORY OF PHARMACOLOGY
Prehistoric people undoubtedly recognized the beneficial or toxic effects of many plant and animal materials. Early written records from China and Egypt and the traditions of India list remedies of many types, including a few that are still recognized as useful drugs today. Most, however, were worthless or actually harmful. In the 1500 years or so preceding the present, there were sporadic attempts to introduce rational methods into medicine, but none was successful owing to the dominance of systems of thought that purported to explain all of biology and disease without the need for experimentation and observation.
These schools promulgated bizarre notions such as the idea that 19th, and early 20th centuries laid the foundation needed for understanding how drugs work at the organ and tissue levels. Paradoxically, real advances in basic pharmacology during this time were accompanied by an outburst of unscientific claims by manufacturers and marketers of worthless “patent medicines.
Not until the concepts of rational therapeutics, especially that of the controlled clinical trial, were reintroduced into medicine— only about 60 years ago—did it become possible to accurately evaluate therapeutic claims.
Pharmacology & Genetics
It has been known for centuries that certain diseases are inherited, and we now understand that individuals with such diseases have a heritable abnormality in their DNA. During the last 10 years, the genomes of humans, mice, and many other organisms have been decoded in considerable detail. This has opened the door to a remarkable range of new approaches to research and treatment. It is now possible in the case of some inherited diseases to define exactly which DNA base pairs are anomalous and in which chromosome they appear.
In a small number of animal models of such diseases, it has been possible to correct the abnormality by gene therapy, ie, insertion of an appropriate “healthy” gene into somatic cells. Human somatic cell gene therapy has been attempted, but the technical difficulties are great. Studies of a newly discovered receptor or endogenous ligand are often confounded by incomplete knowledge of the exact role of that receptor or ligand.
One of the most powerful of the new genetic techniques is the ability to breed animals (usually mice) in which the gene for the receptor or its endogenous ligand has been “knocked out,” ie, mutated so that the gene product is absent or nonfunctional. Homozygous knockout mice usually have complete suppression of that function, whereas heterozygous animals usually have partial suppression.
Observation of the behavior, biochemistry, and physiology of the knockout mice often defines the role of the missing gene product very clearly. When the products of a particular gene are so essential that even heterozygotes do not survive to birth, it is sometimes possible to breed “knockdown” versions with only limited suppression of function. Conversely, “knockin” mice, which overexpress certain proteins of interest, have been bred
PHARMACOLOGY & THE PHARMACEUTICAL INDUSTRY
A truly new drug (one that does not simply mimic the structure and action of previously available drugs) requires the discovery of a new drug target , ie, the pathophysiologic process or substrate of a disease. Such discoveries are usually made in public sector institutions (universities and research institutes), and the molecules that have beneficial effects on such targets are often discovered in the same laboratories.
However, the development of new drugs usually takes place in industrial laboratories because optimization of a class of new drugs requires painstaking and expensive chemical, pharmacologic, and toxicologic research. In fact, much of the recent progress in the application of drugs to disease problems can be ascribed to the pharmaceutical industry including “big pharma,” the multibillion-dollar corporations that specialize in drug discovery and development
The Physical Nature of Drugs
Drugs may be solid at room temperature (eg, aspirin, atropine), liquid (eg, nicotine, ethanol), or gaseous (eg, nitrous oxide). These factors often determine the best route of administration. The most common routes of administration are described in Table 3–3 . The various classes of organic compounds—carbohydrates, proteins, lipids, and their constituents—are all represented in pharmacology.
As noted above, oligonucleotides, in the form of small segments of RNA, have entered clinical trials and are on the threshold of introduction into therapeutics. A number of useful or dangerous drugs are inorganic elements, eg, lithium, iron, and heavy metals. Many organic drugs are weak acids or bases. This fact has important implications for the way they are handled by the body, because pH differences in the various compartments of the body may alter the degree of ionization of such drugs