Hydrochlorothiazide‐Induced ¹³¹I Excretion Facilitated by Salt and Water

Abstract: Salt intake is restricted under clinical conditions for which thiazide diuretics are customarily used. Dietary iodide intake offsets any effect of thiazide on iodide loss. However, our correlation coefficients relating Na⁺ to Cl⁻ to l⁻ excretion indicate that as thiazide administration or sodium chloride intake increases renal Na⁺ and Cl⁻ excretion, l⁻ reabsorption by the nephron coordinately decreases. Increased sodium chloride and water intake by the dog doubled l⁻excretion rates. Hydrochlorothiazide increased the sodium chloride and water enhanced l⁻excretion rate as much as eight‐fold. Without added NaCl, hydrochlorothiazide increased the excretion rate of ¹³¹I by three‐ to eightfold, acutely. Within five to seven days after ¹³¹I oral administration, hydrochlorothiazide (1 or 2 mg/kg twice daily) doubled the rate of ¹³¹I disappearance from plasma, reduced the fecal output of ¹³¹I, and increased its rate of renal excretion. When hydrochlorothiazide was administered, as much ¹³¹I was excreted in the first 24 hours as occurred in 48 hours when sodium chloride and water were given without hydrochlorothiazide. Thiazide administration in customary clinical dosage twice a day with substantial sodium chloride and water for the first two days after exposure to ¹³¹I, should therefore facilitate the safe excretion of ¹³¹I. This accelerated removal of ¹³¹I might be enhanced even more if thyroid uptake of ¹³¹I is blocked by administration of potassium iodide, as judged by the greater ¹³¹I recovery from thyroidectomized dogs. 1981 American College of Clinical Pharmacology