Text 28. SOURCES OF DRUGS AND MECHANISMS OF THEIR ACTION

Drugs of medical value are obtained from mineral, animal and plant sources. An increasing number of organic drugs are obtained by synthesis in the chemical laboratories.

Mineral drugs received from crude natural minerals have been used throughout the centuries and are still used today in purified form. Such minerals as iodine, copper, manganese, cobalt and others are employed in the treatment of many diseases. They are contained in various polyvitamins. Such wide-spread mineral as iron oxide was used by the ancient Greek physician in the treatment of anemia. Today iron in purifies form constitutes specific therapy for certain types of anemia.

Since the earliest records of medicine the organs of animals have been used in the treatment of diseases. Originally this treatment was entirely empirical. Today, it represents one of the greatest achievements of modern medicine. Extracts or whole organs are employed therapeutically in replacement therapy. Desiccated thyroid gland is used in treatment of thyrodism. Insulin extracted from the pancreas – in the treatment of diabetes mellitus. A purifies extract of the anterior pituitary can be used to stimulate production of hormones by the adrenal cortex.

Vegetable drugs derived from plants represent the widest source of natural medicines. The roots, leaves, flowers, seeds and other parts of plants were the principal sources of drugs used by a primitive man. Nowadays a wide variety of substances of plant origin are employed in medicine. Some vegetable drugs, such as belladonna, opium, and digitalis have no satisfactory substitutes. Despite the extensive development of drug synthesis in chemical laboratories and pharmaceutical plants, medicine is still dependent upon nature for many important drugs.

Currently the most fruitful source of drugs is the organic chemistry laboratory. Many drugs are produced there in a more pure state. The use of pure drugs is the ultimate objective of the pharmacologist. In recent years pharmacologists and chemists have been very successful in producing drugs for prevention, treatment and alleviation of diseases. An outstanding example is sulfonamides. These medicines were first produced in 1935 exclusively in a chemical laboratory. They became “miracle” drugs which gave immediate and amazing results in the treatment of many infectious diseases including pneumonia.

Due to discovery of effective and pure drugs the individual of today can live longer and be healthier than ever before.

Drugs used in therapy act upon the body by the following ways: a) stimulation; b) depression; c) irritation; d) replacement therapy and e) chemotherapy. But a drug may possess more than one activity and that is why it may fit in more than one category. Thus, the above classification of types of drug actions can be used with certain limitations.

Stimulation means increasing the activity of specialized cells. For example, caffeine stimulates or increases the reflex activity of the spinal cord. When stimulation is prolonged, the protoplasm becomes depressed and is finally paralyzed. Function is lost from repeated stimulation by drugs or by electric current. Anatomic lesions are not produced, and ordinarily the tissue recovers function after sufficient rest.

Drug depression decreases the activity of specialized cells. Depressive action of drugs is quite selective for special cells. The barbiturates depress the central nervous system. Codeine depresses the cough centre in the medulla. The diminished function is usually a reversible process as the effective dose is metabolized.

Drug irritation refers to the action of a drug on the nourishment, growth, and morphology of the cell. Irritation may be of various degrees. Mild irritation may be used to stimulate activity of tissues. Many cathartic drugs stimulate peristalsis and evacuation in the digestive tract by irritating the mucosal cells. But at the same time excessive doses sometimes result in intestinal bleeding.

Replacement therapy refers to the use of extracts of organs, dried organ tissue, or their synthetic substitutes in the treatment of a deficiency state. If a patient suffers from hypothyroidism (thyroid gland deficiency), the administration of thyroxin, the thyroid hormone, would constitute drug replacement therapy. The use of insulin in the treatment of diabetes mellitus is another example of replacement therapy.

Chemotherapy is administered to attenuate or kill pathogenic organisms without toxicity to the host. The main task in using chemotherapy is to achieve a wide safety and general therapeutic value with the minimal toxicity to the patient. Not all drugs are directed at the cause of disease. Much therapy is only symptomatic. It may relieve the symptoms but doesn’t remove etiologic factor. Thus, morphine does not assist in wound healing or cancer treatment, but it allows the patient to sleep and rest. In these cases relief of symptoms may be very important in facilitating the normal tissue repair processes. It may also have a favourable effect upon possible recovery.