A comparative study of standard and slow-release oral lithium carbonate products.

Lithium serum levels were drawn over one steady-state dosing interval in 8 bipolar disorder patients receiving long-term lithium therapy: (i) after standard-release lithium (STD); and (ii) after changing to 2 weeks' continuous dosing of a slow-release (SR) preparation. Rate of absorption of the SR preparation was significantly slower than the STD preparation measured by the peak/trough difference, percentage peak/trough fluctuation and percentage swing. The extent of absorption measured by the area under the concentration time curve was not significantly different for the two preparations. Serum lithium levels drawn within 2 hours after administration of the SR preparation are likely to be within the range 0- -18% of the 12-hour standard serum lithium with a 95% limit of confidence. The STD preparation shows a deviation in the same period of -14.5-70%. These results suggest that if a patient taking the SR preparation presents within 2 hours after administration a serum lithium level would still be meaningful, whereas for a patient taking the STD preparation it is essential that blood be drawn 12 hours after administration for meaningful interpretation.