Lithium concentrations in plasma of lithium-treated psychiatric patients in the Netherlands: commentary on Cusin et al.

Seasonal variations in 68 psychiatric patients receiving prophylactic lithium treatment in the Netherlands between 1974 and 1994 were analyzed and compared with findings from Italy. Although lithium doses remained stable, there was a significant change in plasma levels of lithium, with values in spring and summer tending to exceed those in autumn and winter. These findings are similar to those reported in Italy, although the maximal seasonal change was approximately 5% in the Netherlands compared with approximately 10% in Italy. The difference could reflect the hotter summer climate in Italy, associated with increased perspiration. Future studies should measure perspiration levels directly.