Midodrine

Midodrine (brand names Amatine, ProAmatine, Gutron) is a vasopressor/antihypotensive agent. Midodrine was approved in the United States by the Food and Drug Administration (FDA) in 1996 for the treatment of orthostatic hypotension. 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.

Mechanism of action
Midodrine is a prodrug which forms an active metabolite, desglymidodrine, which is an α1-receptor agonist 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, and is therefore not associated with effects on the central nervous system.



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