The diuretic and saluretic effects of methyclothiazide result from a drug-induced inhibition of renal tubular reabsorption of electrolytes. The excretion of sodium and chloride is greatly enhanced. Potassium excretion is also enhanced to a variable degree, as it is with the other thiazides. Although urinary excretion of bicarbonate is increased slightly, there is usually no significant change in urinary pH. Methyclothiazide has a per mg natriuretic activity approximately 100 times that of the prototype thiazide, chlorothiazide. At maximal therapeutic dosages, all thiazides are approximately equal in their diuretic/natriuretic effects.

There is significant natriuresis and diuresis within two hours after administration of a single dose of methyclothiazide. These effects reach a peak in about six hours and persist for 24 hours following oral administration of a single dose.

Like other benzothiadiazines, methyclothiazide also has antihypertensive properties, and may be used for this purpose either alone or to enhance the antihypertensive action of other drugs. The mechanism by which the benzothiadiazines, including methyclothiazide, produce a reduction of elevated blood pressure is not known. However, sodium depletion appears to be involved.

Methyclothiazide is rapidly absorbed and slowly eliminated by the kidneys as intact drug but primarily as an inactive metabolite. Additional information on the pharmacokinetics is not known at this time.

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