An antihypotensive agent, also known as a vasopressor agent or simply vasopressor, or pressor, is any medication that tends to raise low blood pressure. Some antihypotensive drugs act as vasoconstrictors to increase total peripheral resistance, others sensitize adrenoreceptors to catecholamines - glucocorticoids, and the third class increase cardiac output - dopamine, dobutamine.
If low blood pressure is due to blood loss, then preparations increasing volume of blood circulation—plasma-substituting solutions such as colloid and crystalloid solutions (salt solutions)—will raise the blood pressure without any direct vasopressor activity. Packed red blood cells, plasma or whole blood should not be used solely for volume expansion or to increase oncotic pressure of circulating blood.[medical citation needed] Blood products should only be used if reduced oxygen carrying capacity or coagulopathy is present.[medical citation needed] Other causes of either absolute (dehydration, loss of plasma via wound/burns) or relative (third space losses) vascular volume depletion also respond, although blood products are only indicated if significantly anemic.
Antihypotensive agents can be classified as follows: