indication

Used in the treatment of oedema (including that associated with heart failure) and hypertension.

pharmacology

Trichloromethiazide is indicated as adjunctive therapy in edema associated with congestive heart failure, hepatic cirrhosis, and corticosteroid and estrogen therapy. Trichloromethiazide has also been found useful in edema due to various forms of renal dysfunction such as nephrotic syndrome, acute glomer-ulonephritis, and chronic renal failure. Trichloromethiazide is also indicated in the management of hypertension either as the sole therapeutic agent or to enhance the effectiveness of other antihypertensive drugs in the more severe forms of hypertension. Like other thiazides, Trichloromethiazide promotes water loss from the body (diuretics). They 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

Trichlormethiazide appears to block the active reabsorption of chloride and possibly sodium in the ascending loop of Henle, altering electrolyte transfer in the proximal tubule. This results in excretion of sodium, chloride, and water and, hence, diuresis. As a diuretic, Trichloromethiazide inhibits active chloride reabsorption at the early distal tubule via the Na-Cl cotransporter, resulting in an increase in the excretion of sodium, chloride, and water. Thiazides like Trichloromethiazide also inhibit sodium ion transport across the renal tubular epithelium through binding to the thiazide sensitive sodium-chloride transporter. This results in an increase in potassium excretion via the sodium-potassium exchange mechanism. The antihypertensive mechanism of Trichloromethiazide is less well understood although it may be mediated through its action on carbonic anhydrases in the smooth muscle or through its action on the large-conductance calcium-activated potassium (KCa) channel, also found in the smooth muscle.

toxicity

Oral Rat LD₅₀ = 5600 mg/kg, oral Mouse LD₅₀ = 2600 mg/kg

drug interactions

Amifostine: Trichlormethiazide may increase the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Trichlomethiazide should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Cholestyramine: The bile acid sequestrant, Cholestyramine resin, may inhibit the absorption of Trichlormethiazide.

Colesevelam: The bile acid sequestrant, Colesevelam, may inhibit the absorption of Trichlormethiazide.

Colestipol: The bile acid sequestrant, Colestipol, may inhibit the absorption of Trichlormethiazide.

Digoxin: Possible electrolyte variations and arrhythmias

Dofetilide: Trichlormethiazide may increase Dofetilide serum concentrations and increase the QTc-prolonging effect of Dofetilide. Increased risk of ventricular arrhythmias.

Lithium: Trichlormethiazide may increase the serum concentration of Lithium by decreasing Lithium excretion. Monitor for changes in the therapeutic/adverse effects of Lithium if Trichlorthiazide is initiated, discontinued or dose changed.

Rituximab: Additive antihypertensive effects may occur. Increased risk of hypotension. Consider withholding Trichlormethiazide for 12 hours prior to administration of Rituximab.

Trandolapril: The thiazide diuretic, Trichlormethiazide, may increase the hypotensive effect of Trandolapril. Trichlormethiazide 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.