Thiazide-Associated Hyponatremia, Report of the Hyponatremia Registry: An Observational Multicenter International Study.

BACKGROUND: Hyponatremia is a frequent and potentially life-threatening adverse side effect of thiazide diuretics. This sub-analysis of the Hyponatremia Registry database focuses on current management practices of thiazide-associated hyponatremia (TAH) and compares differences between TAH and syndrome of inappropriate antidiuretic hormone secretion (SIADH).

METHODS: We analyzed 477 patients from 225 US and EU sites with euvolemic hyponatremia ([Na+] ≤130 mEq/L) who were receiving a thiazide diuretic. Of these, 118 met criteria for true thiazide-induced hyponatremia (TIH).

RESULTS: Thiazide was withdrawn immediately after hyponatremia was diagnosed only in 57% of TAH; in these patients, the median rate of [Na+] change (Δdaily[Na+]) was significantly higher than those with continued thiazide treatment (3.8 [interquartile range: 4.0] vs. 1.7 [3.8] mEq/L/day). The most frequently employed therapies were isotonic saline (29.6%), fluid restriction (19.9%), the combination of these two (8.2%), and hypertonic saline (5.2%). Hypertonic saline produced the greatest Δdaily[Na+] (8.0[6.4] mEq/L/day) followed by a combination of fluid restriction and normal saline (4.5 [3.8] mEq/L/day) and normal saline alone (3.6 [3.5] mEq/L/day). Fluid restriction was markedly less effective (2.7 [2.7] mEq/L/day). Overly rapid correction of hyponatremia occurred in 3.1% overall, but in up to 21.4% given hypertonic saline. Although there are highly significant differences in the biochemical profiles between TIH and SIADH, no predictive diagnostic test could be derived.

CONCLUSIONS: Despite its high incidence and potential risks, the management of TAH is often poor. Immediate withdrawal of the thiazide is crucial for treatment success. Hypertonic saline is most effective in correcting hyponatremia but associated with a high rate of overly rapid correction. We could not establish a diagnostic laboratory-based test to differentiate TIH from SIADH.