Serum lithium levels and long-term diuretic use.

In normal volunteers whose conditions were stablized with lithium carbonate, there were no significant changes in serum lithium levels during a two-week period while they received 40 mg/day of furosemide. During another two-week period, a 50 mg/day dosage of hydrochlorothiazide did cause a significant rise in serum lithium levels. These observations suggest that a substantial amount of lithium and a loop diuretic may not require modification of the lithium dosage.