24-HOUR LITHIUM CONCENTRATION IN HUMAN BRAIN STUDIED BY LI-7 MAGNETIC-RESONANCE SPECTROSCOPY

Brain and serum lithium concentrations were measured every second hour during a 24-hr period following lithium intake, and again 48-hr later in two normal subjects in steady state lithium treatment receiving li thium carbonate (Priadel Synthelabo) once every evening. The brain-lit hium concentration was measured by Li-7 magnetic resonance spectroscop y (MRS). The brain lithium level was found to undulate in a peak-troug h pattern that followed the serum lithium profile, although in an atte nuated form. The brain/serum lithium concentration ratio varied consid erably during the 48-hr period, ranging from 0.5 to 1.3, but the ratio was independent of the serum-lithium concentration. The median half-l ife for lithium was 28 hr in the brain, and 16 hr in serum. The brain lithium concentration in the morning was about 75% of the clinically r elevant standard 12-hr serum lithium concentration The finding that br ain lithium undulates during the day means that MRS measurements of br ain lithium can only be compared if carried out under standard conditi ons that include a fixed interval following lithium intake and an iden tical treatment regimen.