Effect of assay methodology on the prediction of lithium maintenance dosage

Test dose methods have been used to predict the maintenance dosage of lithium carbonate tablets in bipolar patients. These methods require a lithium analytical method that is accurate to the second decimal place. Successful use of these test methods has employed the atomic absorption spectrophotometric method, yet many hospitals use a flame spectrophotometric method. We evaluated a two-point method to predict lithium maintenance dosages of slow-release lithium carbonate tablets in 20 bipolar patients using both assay methodologies. No clinically significant differences were found between the two sets of predictions, suggesting that either assay methodology has requisite sensitivity and accuracy for use in test dose predictions of lithium maintenance dosages.