Hypocalciuric effect of lithium in man

In 7 patients mean urinary calcium excretion decreased from 210 to 93 mg/day (p<0.025) after 3-4 weeks of lithium treatment. This hypocalciuric effect of lithium occurred in the absence of changes in urinary sodium (118 vs. 116 mEq/day), phosphorus (1,073 vs. 1,017 mg/day), cyclic AMP excretion (4.99 vs. 4.75 μmol/g creatinine) and creatinine clearance (106 ± 13 vs. 104 ±11ml/min). Parathyroid hormone (PTH) increased modestly in ± 11 ml/min). of 7 patients during the lithium treatment period; this change was, however, not statistically significant. Total serum calcium remained unchanged (9.7 vs. 9.6 mg/100 ml) but a modest rise in ionized calcium (4.6-4.9 mg/100 ml, p<0.005) did occur with lithium. An exogenous PTH infusion increased urinary cyclic AMP excretion and decreased tubular phosphate reabsorption to comparable degree both before and during lithium treatment. These results, therefore, suggest that lithium therapy increases renal tubular calcium reabsorption; this effect could be secondary to a direct effect of lithium or lithium-induced extrarenal events.