Reduced renal calcium excretion during lithium therapy.

The renal excretion of calcium was determined in ten subjects before and at intervals during 3 months of lithium treatment. The calcium excretion fell by more than 40% within the first week of treatment and remained low throughout the treatment period. The reduction in urinary calcium excretion could be accounted for by an increase in fractional tubular reabsorption of calcium. There were no changes in serum calcium or inorganic phosphate, nor in urinary inorganic phosphate. The results indicate that lithium interferes with the regulation of calcium metabolism.