<prompt> For therapeutic effect in manic depressive illness, steady-state serum lithium concentration should be maintained between0.2-0.4 mEqL0.5-0.8 mEqL1.0-1.3 mEqL1.5-2.5 mEqL  <response>: The margin of safety is narrow for lithium. monitoring of serum lithium concentration is essential for optimising therapy. Serum lithium level is measured 12 hours after the last dose to reflect the steady-state concentration; 0.5-0.8 mEqL is considered optimum for main- tenance therapy in bipolar disorder, while 0.8-1.1 mEqL is required for episodes of acute mania. Toxicity symptoms occur frequently when serum levels exceed 1.5 mEqL. Ref:- kd tripathi;pg num:-449 