Midodrine is a vasopressor/antihypotensive agent. Midodrine was approved in the United States by the Food and Drug Administration

Food and Drug Administration

The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 (FDA) in 1996 for the treatment of orthostatic hypotension

Orthostatic hypotension

Orthostatic hypotension, also known as postural hypotension, orthostasis, and colloquially as head rush or dizzy spell, is a form of hypotension in which a person's blood pressure suddenly falls when the person stands up or stretches. The decrease is typically greater than 20/10 mm Hg, and may be...

. In August 2010, the FDA proposed withdrawing this approval because the manufacturer, Shire plc, has failed to complete required studies after the medicine reached the market.

In September of 2010, the FDA reversed in decision to remove Midodrine from the market and has allowed it to remain available to patients while Shire plc collects further data regarding the efficacy and safety of the drug. Shire plc announced on September 27, 2011 that it was continuing the process to work with the FDA towards a final approval of the drug.

Chemical properties

Midodrine is an odorless, white, crystalline powder, soluble in water and sparingly soluble in methanol

Methanol

Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

.

Mechanism of action

Midodrine is a prodrug

Prodrug

A prodrug is a pharmacological substance administered in an inactive form. Once administered, the prodrug is metabolised in vivo into an active metabolite, a process termed bioactivation. The rationale behind the use of a prodrug is generally for absorption, distribution, metabolism, and...

 which forms an active metabolite

Metabolite

Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...

, desglymidodrine, which is an α₁-receptor

Alpha-1 adrenergic receptor

The alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic...

 agonist

Agonist

An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

 and exerts its actions via activation of the alpha-adrenergic receptors of the arteriolar and venous vasculature, producing an increase in vascular tone and elevation of blood pressure. Desglymidodrine does not stimulate cardiac beta-adrenergic receptors. Desglymidodrine diffuses poorly across the blood-brain barrier

Blood-brain barrier

The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...

, and is therefore not associated with effects on the central nervous system

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

.

Metabolism

After oral administration, midodrine is rapidly absorbed. The plasma levels of the prodrug peak after about half an hour, and decline with a half-life of approximately 25 minutes, while the metabolite reaches peak blood concentrations about 1 to 2 hours after a dose of midodrine and has a half-life of about 3 to 4 hours. The absolute bioavailability of midodrine (measured as desglymidodrine) is 93%.

Indications

Midodrine hydrochloride tablets are indicated for the treatment of symptomatic orthostatic hypotension. In a critical care settings, it is widely used as an adjunctive therapy to weaning patients off of intravenous vasopressive medications. It has been suggested also as a treatment for chronic fatigue syndrome

Chronic fatigue syndrome

Chronic fatigue syndrome is the most common name used to designate a significantly debilitating medical disorder or group of disorders generally defined by persistent fatigue accompanied by other specific symptoms for a minimum of six months, not due to ongoing exertion, not substantially...

 as well as for hepato-pulmonary syndrome. It is also used with octreotide

Octreotide

Octreotide is an octapeptide that mimics natural somatostatin pharmacologically, though it is a more potent inhibitor of growth hormone, glucagon, and insulin than the natural hormone...

 for hepatorenal syndrome

Hepatorenal syndrome

Hepatorenal syndrome is a life-threatening medical condition that consists of rapid deterioration in kidney function in individuals with cirrhosis or fulminant liver failure...

; the proposed mechanism is constriction of splanchinc vessels and dilation of renal vasculature.

Contraindications

Midodrine is contraindicated in patients with severe organic heart disease, acute renal disease, urinary retention, pheochromocytoma or thyrotoxicosis. Midodrine should not be used in patients with persistent and excessive supine hypertension.

Side effects

Headache; feeling of pressure/fullness in the head, vasodilation/flushing face, confusion/thinking abnormality, dry mouth; nervousness/anxiety and rash.

External links

• Midodrine at drugs.com