12-HOUR BRAIN LITHIUM CONCENTRATION IN LITHIUM MAINTENANCE TREATMENT OF MANIC-DEPRESSIVE DISORDER - DAILY VERSUS ALTERNATE-DAY DOSING SCHEDULE

The 12-h brain lithium concentration was measured by lithium-7 magneti c resonance spectroscopy in ten manic-depressive patients receiving da ily or alternate-day lithium carbonate treatment. The median dose of l ithium carbonate was 800 mg in the daily treatment group and 1200 mg i n the alternate-day group. Median 12-h serum lithium concentration in the two groups was 0.86 mmol l(-1) and 0.55 mmol l(-1), respectively, while the corresponding concentration in brain was 0.67 mmol l(-1) and 0.52 mmol l(-1), respectively. The 12-h brain lithium concentration w as independent of lithium dosing schedule (multiple linear regression) , but correlated significantly with the 12-h serum lithium concentrati on (P = 0.003; B = 0.53, 95% c.l. 0.24-0.82; beta = 0.83). Thus at ide ntical 12-h serum lithium concentrations the 12-h brain lithium concen tration is similar with both treatment regimes. As the risk of manic-d epressive relapse during alternate-day lithium treatment is in our exp erience 3-fold greater than with daily treatment (at similar mean 12-h serum lithium concentration), the findings suggest that the differenc e in the prophylactic efficacy of the two dosing schedules is unrelate d to differences in the 12-h brain lithium concentration.