Re-exploring Saliva as an Analyte in Estimation of Lithium in Stable Bipolar Patients – A Pilot Study in a Tertiary Care Hospital in West Bengal

Background: Lithium a frequently prescribed drug in the treatment of bipolar affective disorder, due to its inherent adverse potential and narrow therapeutic index, demands for regular therapeutic drug monitoring (TDM). Although the term TDM seems to be tedious, the most tedious job is to collect blood samples from patients with psychiatric illness. In this study, we aimed to find out an alternative method to serum lithium monitoring. Although saliva as an analyte is non-popular, the presence of lithium in the saliva in patients who consumes lithium makes procedure of collection easier. The rate of elimination of lithium is slower from saliva than from serum, which makes the concentration of lithium higher in saliva than in blood. Lithium elimination follows two compartment pharmacokinetic models, where important part of compartment is saliva and salivary glands. The trouble of repeated venipuncture can be done away with, if a non-invasive method for serum lithium concentration is taken into consideration. An alternative method of determining lithium level could be saliva. The aim of this study was to find out whether estimation of lithium in saliva can replace serum lithium estimation. Materials and Methods: In this cross-sectional study, 60 stable patients of bipolar disorder attending psychiatry outdoor on lithium therapy for 3 months or more were considered. After informed consent documentation serum and saliva samples were collected after 12 h of last dose of lithium carbonate intake. Assessment was done based on atomic absorption spectrometry. After statistical analysis, it was found that that there is a correlation between serum and saliva lithium level. The 60 patients were divided into two groups, consisting of 30 patients each. Linear regression was done in both the groups thereby the formula obtained from the first group, was utilized to calculate the saliva concentration form serum concentration. The mean values were compared at the last. Results: The mean serum lithium obtained was 0.99 ± 0.257 SD (mEq/L) and mean salivary lithium obtained was 1.63 ± 0.51 SD (mEq/L) in Group 1. Whereas, the mean serum lithium obtained was 0.79 ± 0.26 SD (mEq/L) and mean salivary lithium obtained was 1.67 ± 0.49 SD (mEq/L) in group 2. Lithium concentration from both the samples showed a positive correlation as obtained from the scatter plot. Conclusion: Salivary Li estimation seems to yield positive results, yet more research should be done in this regard. Since saliva method for estimation is non-invasive, the idea could be utilized in designing other devices