Renal function in 32 patients treated with lithium for an average period of 10 years was reexamined 2 years after the first examination. A markedly influenced tubular function leading to increased urine volume (average 3 litres/24 h) and decreased renal concentrating capacity was still found, whereas glomerular function remained unimpaired in nearly all of the patients. No statistically significant changes in renal functions were observed at the follow-up examination. The results were compared with the same renal functional tests obtained from a control group consisting of 53 patients with affective disorders never treated with lithium. The control group had a significantly lower urine output (average 2 litres/24 h), but lithium-treated patients on a one-dose schedule had an average urine volume of only 500 ml/24 h more than the controls. In conclusion, this prospective study found no evidence of a progressive impairment of glomerular or tubular function in lithium-treated patients reexamined after 2 years. Patients with affective disorders never treated with lithium had normal renal concentrating capacity.

Renal structure and function were investigated in two groups of long-term lithium treated patients. Lithium was administered in two different ways either in a one-dose per day schedule where the whole dose of lithium was given between 8 and 10 p.m. or in a schedule where the lithium dose was given, divided into two or three doses, during the day. Kidney biopsy was performed, and structural changes in the kidney tissue were determined together with 24-h urine volume in the individual patients. The functional as well as the structural changes were most pronounced in patients given their lithium in divided doses during the day. Lithium may be more harmful to the kidney when the lithium administration gives a relatively constant serum lithium level than when the administration causes greater variations including peak values and low minimum levels in serum lithium. The reason for this might be that a number of regenerative processes only occur in periods with low lithium concentrations.

For many year two Danish psychiatric hospitals having used different lithium treatment regimens. In one, slow-release tablets were given in two daily doses and, in the other conventional tablets were given in a single daily dose. In both hospitals many patients developed polyuria. Multiple regression analyses with sex, age, treatment duration, serum lithium concentration, and treatment regimen as predictor variables showed that the two treatment regimens did not affect the glomerular filtration rate or the proximal reabsorption differently, but that distal water reabsorption was significantly less affected and polyuria less pronounced in the patients given conventional tablets once daily than in those give slow-release tablets twice daily. The authors are divided among themselves as regards the implications of these findings.

46 patients treated with lithium for an average of 8 years participated in a functional-morphological follow-up study based on a 12-day hospitalization and involving a kidney biopsy. The functional part of the study showed that tubular function was markedly influenced, leading to increased urine volume (average 3 1/24 h) and a decreased renal concentration capacity in 85% of the patients. Glomerular function was generally not influenced, and only 10% of the patients had glomerular filtration rates below their age-corrected normal ranges. Both urine volume and glomerular filtration rates showed significant correlations with dosage schedule. Urine volume was lower and glomerular filtration rate higher on a one-dose schedule than when lithium was given in divided doses during the day. It is concluded that discontinuity in lithium treatment minimizes lithium effects on kidney function.