Comparative effects of potassium chloride and bicarbonate on thiazide-induced reduction in urinary calcium excretion

Background. The chronic low-grade metabolic acidosis that occurs in various renal disorders and in normal people, and that is related both to dietary net acid load and age-related renal functional decline, may contribute to o steoporosis by increasing urine calcium excretion. Administration of potass ium (K) alkali salts neutralizes acid and lowers urine calcium excretion. U rine calcium excretion also can be reduced by the administration of thiazid e diuretics, which are often given with supplemental K to avoid hypokalemia . We determined whether the K alkali salt potassium bicarbonate (KHCO3) and the thiazide diuretic hydrochlorothiazide (HCTZ) combined is more effectiv e in reducing urinary calcium than KHCO3 alone or HCTZ combined with the co nventionally coadministered non-alkalinizing K salt potassium chloride (KCl ). Methods. Thirty-one healthy men and women aged 50 or greater were recruited for a four-week, double-blind, randomized study. After a baseline period o f 10 days with three 24-hour urine and arterialized blood collections, subj ects were randomized to receive either HCTZ (50 mg) plus potassium (60 mmol daily) as either the chloride or bicarbonate salt. Another 19 women receiv ed potassium bicarbonate (60 mmol) alone. After two weeks, triplicate colle ctions of 24-hour urines and arterialized bloods were repeated. Results, Urinary calcium excretion decreased significantly in all groups. K HCO3 alone and HCTZ + KCl induced similar decreases (-0.70 +/- 0.60 vs. -0. 80 +/- 1.0 mmol/day, respectively). Compared with those treatments, the com bination of HCTZ + KHCO3 induced more than a twofold greater decrease in ur inary calcium excretion (-1.8 +/- 1.2 mmol/day, P < 0.05). Both HCTZ + KHCO 3 and KHCO3 alone reduced net acid excretion significantly (P < 0.05) to va lues of less than zero. Conclusions. KHCO3 was superior to KCl as an adjunct to HCTZ, inducing a tw ofold greater reduction in urine calcium excretion, and completely neutrali zing endogenous acid production so as to correct the pre-existing mild meta bolic acidosis that an acid-producing diet usually induces in older people. Accordingly, for reducing urine calcium excretion in stone dis-ease and os teoporosis, the combination of HCTZ + KHCO3 may be preferable to that of HC TZ + KCl.