On the elimination half‐life of lithium in long‐term treatment of patients with affective disorders

Abstract

The elimination half‐life of lithium was investigated in 55 patients on long‐term treatment in 1980, when their mean treatment time was 7·5 years. Twenty‐seven of the patients were reinvestigated 7 years later, at which point their mean treatment time was 15 years. An approximate method for determining the elimination half‐life of lithium was used, and this variable was tested in eight chronic psychotic patients on lithium treatment, in whom the elimination half‐life was also determined by a conventional technique. The elimination half‐life was 32 h in 1980 and varied between 15 and 128 h. The elimination half‐life was significantly increased 7 years later, with a median increase of 8 h. The elimination half‐life of lithium was closely correlated to age and to daily weight‐related dose of lithium when the patients entered the study in 1980, but this was not seen at the time of the reinvestigation in 1987. The elimination half‐life did not vary with serum creatinine, maximal urine osmolality, or with the concomitant neuroleptic medication. Further studies are needed to clarify the clinical significance of the prolonged elimination half‐life with time.