9.4 : 降圧薬: サイアジド系利尿薬

Thiazide-type diuretics feature a benzothiadiazine ring, while thiazide-like diuretics lack the ring structure.

Thiazide-class of diuretics inhibit the Na⁺/Cl^- symporter present on the luminal membrane of the epithelial cells lining the distal convoluted tubule of the nephron.

This inhibition prevents the movement of Na⁺ and Cl^- ions from the tubular fluid into the epithelial cells, reducing their reabsorption into the blood.

As the ions remain in the lumen, they draw more water, resulting in diuresis and increased urine excretion.

The increased urine output reduces blood volume, leading to a decrease in cardiac output and a decrease in blood pressure.

Thiazides also inhibit calcium influx into vascular smooth muscle cells, promoting muscle relaxation and reducing peripheral resistance through vasodilation, further lowering blood pressure.

For significant diuretic effects, thiazides need to be excreted through urine. Their efficacy is reduced in patients with impaired renal function, such as those with a decreased glomerular filtration rate and impaired tubular secretion.