indication

Used as adjunctive therapy in edema associated with congestive heart failure, hepatic cirrhosis, and corticosteroid and estrogen therapy. Also used in the management of hypertension either as the sole therapeutic agent or to enhance the effect of other antihypertensive drugs in the more severe forms of hypertension.

pharmacology

Hydroflumethiazide is an oral thiazide used to treat hypertension and edema. High blood pressure adds to the workload of the heart and arteries. If it continues for a long time, the heart and arteries may not function properly. This can damage the blood vessels of the brain, heart, and kidneys, resulting in a stroke, heart failure, or kidney failure. High blood pressure may also increase the risk of heart attacks. Like other thiazides, Hydroflumethiazide promotes water loss from the body (diuretics). Thiazides inhibit Na+/Cl- reabsorption from the distal convoluted tubules in the kidneys. Thiazides also cause loss of potassium and an increase in serum uric acid. Thiazides are often used to treat hypertension, but their hypotensive effects are not necessarily due to their diuretic activity. Thiazides have been shown to prevent hypertension-related morbidity and mortality although the mechanism is not fully understood. Thiazides cause vasodilation by activating calcium-activated potassium channels (large conductance) in vascular smooth muscles and inhibiting various carbonic anhydrases in vascular tissue.

mechanism of action

Hydroflumethiazide is a thiazide diuretic that inhibits water reabsorption in the nephron by inhibiting the sodium-chloride symporter (SLC12A3) in the distal convoluted tubule, which is responsible for 5% of total sodium reabsorption. Normally, the sodium-chloride symporter transports sodium and chloride from the lumen into the epithelial cell lining the distal convoluted tubule. The energy for this is provided by a sodium gradient established by sodium-potassium ATPases on the basolateral membrane. Once sodium has entered the cell, it is transported out into the basolateral interstitium via the sodium-potassium ATPase, causing an increase in the osmolarity of the interstitium, thereby establishing an osmotic gradient for water reabsorption. By blocking the sodium-chloride symporter, Hydroflumethiazide effectively reduces the osmotic gradient and water reabsorption throughout the nephron.

toxicity

Overdoses lead to diuresis, lethargy progressing to coma, with minimal cardiorespiratory depression and with or without significant serum electrolyte changes or dehydration.

biotransformation

Essentially unchanged

absorption

Hydroflumethiazide is incompletely but fairly rapidly absorbed from the gastrointestinal tract

half life

It appears to have a biphasic biological half-life with an estimated alpha-phase of about 2 hours and an estimated beta-phase of about 17 hours

drug interactions

Digoxin: Possible electrolyte variations and arrhythmias

Lithium: The thiazide diuretic, hydroflumethiazide, may increase serum levels of lithium.

Trandolapril: The thiazide diuretic, Hydroflumethiazide, may increase the hypotensive effect of Trandolapril. Hydroflumethiazide may also increase the nephrotoxicity of Trandolapril. Monitor for postural hypotension at initiation of concomitant therapy and renal dysfunction during chronic therapy.

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.