Clinical meaning
Understanding the distinct mechanisms of action (MOA) of mood stabilizers is essential for selecting appropriate agents, predicting drug interactions, and designing monitoring protocols. Lithium's mechanism centers on intracellular second messenger modulation: inhibition of inositol monophosphatase depletes phosphatidylinositol bisphosphate (PIP2) substrate, attenuating protein kinase C (PKC) and diacylglycerol (DAG) signaling in overactive neurons while sparing normally functioning cells (the inositol depletion hypothesis). Lithium's inhibition of GSK-3β stabilizes beta-catenin and circadian clock proteins, normalizing the disrupted circadian rhythms characteristic of bipolar disorder. Because lithium is renally excreted with a narrow therapeutic index (0.6-1.2 mEq/L), monitoring requires serial trough levels, renal function (creatinine, GFR every 6 months), and thyroid function (TSH every 6 months) because lithium inhibits thyroid hormone release and can cause clinical hypothyroidism in 20-30% of patients and rarely hyperparathyroidism through parathyroid gland stimulation. Valproate's dual mechanism (GABA enhancement via GABA transaminase inhibition plus sodium channel blockade) provides rapid antimanic efficacy. Monitoring requires hepatic function panels (risk of fatal hepatotoxicity, particularly in children under 2 on polytherapy), CBC with platelets (dose-dependent thrombocytopenia), ammonia levels when lethargy develops (hyperammonemic encephalopathy can occur...