Changes in Plasma and Extracellular Fluid Volumes in Patients with Essential Hypertension During Long-Term Treatment with Hydrochlorothiazide

In 13 untreated patients with essential hypertension, the plasma volume (T-1824) and the extracellular fluid volume (82Brdistribution space) were determined three times. During treatment with 50 to 100 mg of hydrochlorothiazide daily, determinations of plasma volume and extracellular fluid volume were repeated after treatment for 1 mo (13 patients), 2 mo (13 patients), 4 mo (eight patients), and 6 mo ( seven patients). In all cases the average plasma and extracellular fluid volumes were reduced compared with the averages of three control values. The plasma volume was significantly reduced at the 5% level after treatment for 1, 2, and 4 mo. Corresponding studies from the literature have been reviewed and, on the basis of these studies and our own results, it is concluded that thiazides have a volume-depleting effect which is continued during long-term treatment of patients with essential hypertension.