Ticket 16

1. Types of action of medicinal substances.

There are the following types of action: local and resorptive, reflex, direct and indirect, main and side, and some others. The drug has a local effect on contact with tissues at the site of its application (usually skin or mucous membranes). For example, with surface anesthesia, the local anesthetic acts on the endings of the sensory nerves only at the site of application to the mucous membrane. To provide local action, medicinal substances are prescribed in the form of ointments, lotions, rinses, patches. When prescribing certain medicinal substances in the form of eye or ear drops, they also count on their local action. However, a certain amount of the drug is usually absorbed from the site of application into the bloodstream and has a general (resorptive) effect.

Resorptive action (from Lat. Resorbeo - I absorb) - the effects caused by medicinal substances after absorption into the bloodstream or direct injection into a blood vessel and distribution in the body. With a resorptive effect, as with a local one, the substance can excite sensitive receptors and cause reflex reactions.

Direct (primary) action - a change in the functions of organs by drugs as a result of action on the cells of these organs (cardiac glycosides increase heart contractions, blocking Na + -, K + -ATPase of myocardial muscle cells; diuretics increase diuresis, disrupting the reabsorption of ions and water in the kidneys tubules).

Indirect (secondary) effect - a change in the functions of organs and cells by drugs as a result of action on other organs and cells that are functionally related to the former (cardiac glycosides have a diuretic effect, as they increase heart contractions → improve blood flow in the kidneys → increase filtration and urine formation) ...

A special case of indirect action is reflex - a change in the functions of organs due to direct stimulation of sensitive nerve endings. Depolarization of nerve endings causes an impulse, which is transmitted to the executive organs along reflex arcs with the participation of nerve centers. Skin irritants have reflex effects as a result of excitation of exteroreceptors; interoreceptors - expectorant, emetic, choleretic, laxatives; vascular chemoreceptors - analeptics; skeletal muscle proprioceptors - muscle relaxants.

The reversible action is due to the establishment of fragile physicochemical bonds with cytoreceptors, which is typical for most drugs.

An irreversible effect occurs as a result of the formation of covalent bonds with cytoreceptors, which is characteristic of few drugs, usually highly toxic and used topically.

The main action is the therapeutic effects of drugs.

Side effect - additional, undesirable effects.

The pharmacological effects of the same drug can be major or side effects in various diseases. So, in the treatment of bronchial asthma, the main effect of adrenaline is the expansion of the bronchi, with hypoglycemic coma - an increase in glycogenesis and an increase in blood glucose.

Adverse reactions are observed when taking many medicines. Their frequency in outpatient treatment reaches 10 - 20%, and 0.5 - 5% of patients require hospitalization due to complications of pharmacotherapy.

Selective action - the effect of drugs on the functions of only certain organs and systems. It is due to a greater extent to selective binding to cytoreceptors, to a lesser extent to selective accumulation in organs and tissues, although there are examples of drugs creating high concentrations in cells on which they act. Magnesium sulfate, not being absorbed from the intestines, enhances peristalsis and causes a choleretic effect. When administered parenterally, magnesium ions inhibit the central nervous system. Inhalation anesthetic drugs create a concentration in the brain that is 1.5 - 2 times higher than in the blood. Iodine intensively enters only the thyroid gland.