Thiazide-induced hyponatremia. Reproducibility by single dose rechallenge and an analysis of pathogenesis.
OBJECTIVE
To determine whether a single-dose of thiazide administered to patients with previous thiazide-induced hyponatremia will cause hyponatremia and, if so, to analyze its pathogenesis.


METHODS
Prospective controlled study comparing patients with previous thiazide-induced hyponatremia with two control groups.


METHODS
Eleven patients with thiazide-induced (Kaluril [hydrochlorothiazide, 50 mg; amiloride, 5 mg]) hyponatremia of less than 130 mmol/L at least 1 week before the study. Two groups of controls: 10 young healthy volunteers and 11 elderly hypertensive patients previously treated uneventfully with thiazide.


METHODS
Administration of a single dose of hydrochlorothiazide, 50 mg, and amiloride, 5 mg.


METHODS
Blood pressure, pulse rate, body weight, serum urea, creatinine, sodium, potassium, magnesium, osmolality, plasma antidiuretic hormone, renin, aldosterone and also urinary sodium, potassium, osmolality, and cyclic adenosine monophosphate (cAMP) before and 6 to 8, 12, and 24 hours after drug administration.


RESULTS
Within 6 to 8 hours serum sodium decreased in patients, young controls, and elderly controls by 5.5 +/- 1.1 (mean +/- SE), 1.2 +/- 0.4, and 1.8 +/- 0.9 mmol/L, respectively (Py less than 0.001 [patients versus young controls], Pe = 0.017 [patients versus elderly controls]). Serum osmolality decreased in patients, young controls, and elderly controls by 14.9 +/- 2.6, 2.8 +/- 1.6, and 6.6 +/- 1.5 mmol/kg, respectively (Py less than 0.001, Pe = 0.012). All patients and only one control subject reached osmolality of less than 280 mmol/kg. At 6 to 8 hours all patients gained weight (0.85 +/- 0.13 kg) whereas young and elderly controls lost weight (0.47 +/- 0.23 and 0.45 +/- 0.2 kg, respectively) (Py much less than 0.001, Pe much less than 0.001). Patients' responses to the drug did not differ from both control groups regarding sodium and potassium urinary excretion, osmolar and free water clearance, and antidiuretic hormone blood levels. Water restriction in one patient attenuated serum sodium reduction.


CONCLUSIONS
Use of a single-dose of a thiazide diuretic may predict the development of hyponatremia. Increased body weight apparently due to polydipsia may play a major role in the pathogenesis of thiazide-induced hyponatremia.
Friedman
E
E
Chaim Sheba Medical Center, Tel-Hashomer, Israel.
Shadel
M
M
Halkin
H
H
Farfel
Z
Z
D000328:Adult; D001581:Benzothiadiazines; D001834:Body Water / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004198:Disease Susceptibility; D004232:Diuretics; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000139:chemically induced* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009318:Natriuresis / Q000187:drug effects; D009994:Osmolar Concentration; D011188:Potassium / Q000652:urine; D011446:Prospective Studies; D049993:Sodium Chloride Symporter Inhibitors / Q000009:adverse effects*
D001581:Benzothiadiazines; D004232:Diuretics; D049993:Sodium Chloride Symporter Inhibitors; D011188:Potassium