Daranide (Dichlorphenamide) - Description and Clinical Pharmacology

DESCRIPTION

DARANIDE * (Dichlorphenamide) is an oral carbonic anhydrase inhibitor. Dichlorphenamide, a dichlorinated benzenedisulfonamide, is known chemically as 4,5-dichloro-1,3-benzenedisulfonamide. Its empirical formula is C₆H₆Cl₂N₂O₄S₂ and its structural formula is:

Dichlorphenamide is a white or practically white, crystalline compound with a molecular weight of 305.16. It is very slightly soluble in water but soluble in dilute solutions of sodium carbonate and sodium hydroxide. Dilute alkaline solutions of dichlorphenamide are stable at room temperature.

DARANIDE is supplied as tablets, for oral administration, each containing 50 mg dichlorphenamide. Inactive ingredients are D&C Yellow 10, lactose, magnesium stearate, and starch.

*Registered trademark of MERCK & CO., INC.

CLINICAL PHARMACOLOGY

Carbonic anhydrase inhibitors reduce intraocular pressure by partially suppressing the secretion of aqueous humor (inflow), although the mechanism by which they do this is not fully understood. Evidence suggests that HCO₃^- ions are produced in the ciliary body by hydration of carbon dioxide under the influence of carbonic anhydrase and diffuse into the posterior chamber with Na⁺ ions. The aqueous fluid contains more Na⁺ and HCO₃^- ions than does plasma and consequently is hypertonic. Water is attracted to the posterior chamber by osmosis. Systemic administration of a carbonic anhydrase inhibitor has been shown to inactivate carbonic anhydrase in the ciliary body of the rabbit's eye and to reduce the high concentration of HCO₃^- ions in ocular fluids. As is the case with all carbonic anhydrase inhibitors, DARANIDE in high doses causes some decrease in renal blood flow and glomerular filtration rate.

In man, DARANIDE begins to act within an hour and maximal effect is observed in two to four hours. The lowered intraocular tension may be maintained for approximately 6 to 12 hours.