SINGLE-DOSE BIOAVAILABILITY OF 2 EXTENDED-RELEASE LITHIUM-CARBONATE PRODUCTS

The single-dose bioavailabilities of two extended-release lithium carb onate products and an immediate-release product were compared. Nonsmok ing healthy volunteers ages 20-31 (n = 12) were randomly assigned to o ne of three groups and given three treatments, each separated by a one -week period. The treatments, which were given to each group in a diff erent sequence, consisted of three 300-mg immediate-release lithium ca rbonate tab-lets (Lithotab), two 450-mg extended-release lithium carbo nate tablets (Eskalith CR), and three 300-mg extended-release lithium carbonate tablets (Lithobid). Blood samples were collected just before drug administration and at intervals up to 48 hours after-ward. Urine was collected for 96 hours. Plasma and urine lithium concentrations w ere determined by flame-emission spectrophotometry, and lithium pharma cokinetic values and the cumulative urinary excretion of lithium were computed. Mean maximum plasma lithium concentration (C-max) differed s ignificantly among all three lithium carbonate products. Eskalith CR p roduced a 40% lower C-max and lithobid a 25% lower C-max than Lithotab ; Lithobid produced a 23% higher Cmax than Eskalith CR. Lithotab had a significantly shorter mean time to maximum plasma lithium concentrati on than either extended-release product. Much cumulative urinary excre tion of lithium did not differ significantly among the three products. Two extended-release lithium carbonate products were not bioequivalen t when given in single doses to healthy volunteers.