Abstract
Background Lithium is a first line drug used to treat bipolar affective disorder requiring frequent monitoring due to its narrow therapeutic index. Flame photometry is a reliable quick and cost-effective method of serum lithium estimation. Objective We aimed to validate a flame photometry method for serum lithium estimation to compare the results with a different model flame photometer and an ion-selective electrode. Method Sherwood 410 flame photometer was used for the analysis. Serum samples were diluted 1:2 using a lithium blank solution containing sodium and potassium. Aqueous lithium standards were prepared using the same blank. The method was validated for the concentration range 0.2-1.5mmol/l. Linearity, recovery, accuracy, precision and stability were determined by standard lithium serum samples representing the lower limit of quantification (LLOQ) 0.2mmol/l, median level of quantification (MLOQ) 0.8mmol/l and the upper limit of quantification (ULOQ) 1.5mmol/l. Five replicates of serum and aqueous lithium samples were used to determine linearity in the range between LLOQ and ULOQ using the coefficient of determination (R2). Five standard serum replicates were used for recovery, accuracy and precision studies. Precision was determined by the coefficient of variation (CV%) on three different days. Results of the flame photometric method were compared with those of a different flame photometric method and an ion-selective electrode method. Results: The R2 for the aqueous samples and the serum samples was >0.995 demonstrating linearity. The matrix effect ranged between 92.5% and 105% for the LLOQ, MLOQ and ULOQ. The accuracy and precision for LLOQ, MLOQ of and ULOQ were below 15%. Similar results were obtained for the QC samples with the different model flame photometer and ion-selective electrode method. Conclusion The flame photometric method used in our laboratory is suitable and reliable for determining serum lithium concentrations for use in therapeutic drug monitoring.
Highlights
Lithium is a first line drug used to treat bipolar affective disorder requiring frequent monitoring due to its narrow therapeutic index
The matrix effect ranged between 92.5% and 105% for the lower limit of quantification (LLOQ), median level of quantification (MLOQ) and upper limit of quantification (ULOQ)
The accuracy and precision for LLOQ, MLOQ of and ULOQ were below 15%
Summary
Lithium is a first line drug used to treat bipolar affective disorder requiring frequent monitoring due to its narrow therapeutic index. Lithium is of proven efficacy in the treatment of bipolar disorder showing benefit in both the manic phase and the depressive phase. It is effective in the prophylaxis of the condition [1,2]. In order to manage these patients on lithium therapy better, it is recommended to monitor their serum lithium concentrations. Serum lithium concentrations are monitored at initiation of therapy for dose adjustment. Serum lithium concentrations are recommended to be measured every 3-6 months for optimum therapeutic drug monitoring [2,3]. Adverse effects are observed at the therapeutic range, as well as when the serum concentrations exceed the therapeutic range in a dose dependent manner [1]
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