Vasoconstrictor drugs are medicines that cause the blood vessels of the body to narrow. These vessels naturally have the capability to relax and contract as the blood pumps through them, and constricting drugs simply make the vessels narrower than they would otherwise be. Drugs of this class can be useful for people with conditions like shock and low blood pressure. Vasoconstrictor drugs, which are also called vasopressors, are split into two major groups, which are the vasopressin analogs and the alpha-adrenoreceptor agonists.
In a person with a healthy circulatory system, the heart pumps blood through veins and arteries in a heartbeat pattern, which alternates high pressure with low pressure. In order to accommodate the changes in pressure, the blood vessels are covered in muscle, which allows the channel to expand and contract. Vasoconstriction is the scientific term for the contraction of the vessels, which reduces the internal diameter of the hollow vessel. As well as responding to the natural pressure variations of traveling blood, the blood vessels can also constrict in response to environmental factors such as cold, stress and even nicotine from cigarette smoke.
Some medical conditions cause problems with efficient movement of blood around the body. Shock, for example, is a serious condition that can be lethal. Hypotension, which is low blood pressure, can also be dangerous to health. Vasoconstrictor drugs can therefore be a useful tool in treating these conditions. Sometimes, the constricting effect of the drug can be complemented by administration of an additional drug of the inotrope class, which increase the strength of heart contractions.
Two options for vasoconstrictor drugs are available to doctors. One type of medication are drugs that stick to certain receptors on the muscle of the vessels to prevent them from doing the job of expanding the vessel. These receptors are called alpha-adrenoreceptors, and the drugs are therefore called alpha-adrenoreceptor agonists. Examples of specific drugs in this group are methoxamine, tetrahydralazine and clonidine. Possible side effects of this group of drugs include abnormal heartbeat, headache and fluid retention.
The second major type of vasoconstrictor is a molecule similar to a natural hormone called vasopressin. This hormone, and the copy of it present in the drug products, block receptors in the muscle called V1 receptors, and thereby prevent expansion of the vessel. A significant effect of these hormone analogs, as well as vasoconstriction, is water loss from the body. Possible side effects include headache, a feeling of nausea, and elecrolyte deficiency due to excess water loss.