Pharmacology of Midodrine
| Indication | For the treatment of symptomatic orthostatic hypotension (OH). |
| Pharmacodynamics | Midodrine is a prodrug, i.e., the therapeutic effect of orally administered midodrine is due to the major metabolite desglymidodrine formed by deglycination of midodrine. Desglymidodrine diffuses poorly across the blood-brain barrier, and is therefore not associated with effects on the central nervous system. Administration of midodrine results in a rise in standing, sitting, and supine systolic and diastolic blood pressure in patients with orthostatic hypotension of various etiologies. Standing systolic blood pressure is elevated by approximately 15 to 30 mmHg at 1 hour after a 10-mg dose of midodrine, with some effect persisting for 2 to 3 hours. Midodrine has no clinically significant effect on standing or supine pulse rates in patients with autonomic failure. |
| Mechanism of action | Midodrine forms an active metabolite, desglymidodrine, that is an alpha1-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. |
| Absorption | Rapidly absorbed following oral administration. The absolute bioavailability of midodrine (measured as desglymidodrine) is 93% and is not affected by food. |
| Volume of distribution | Not Available |
| Protein binding | Not Available |
| Metabolism | Thorough metabolic studies have not been conducted, but it appears that deglycination of midodrine to desglymidodrine takes place in many tissues, and both compounds are metabolized in part by the liver. |
| Route of elimination | Not Available |
| Half life | 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. |
| Clearance |
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| Toxicity | Symptoms of overdose could include hypertension, piloerection (goosebumps), a sensation of coldness and urinary retention. The single doses that would be associated with symptoms of overdosage or would be potentially life- threatening are unknown. The oral LD50 is approximately 30 to 50 mg/kg in rats, 675 mg/kg in mice, and 125 to 160 mg/kg in dogs. Desglymidodrine is dialyzable. |
| Affected organisms |
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