Half-life of lithium?

Ans. c (24 hours). (Ref. KD Tripathi, 4th ed., 331, 659)LITHIUM# Lithium is a small monovalent cation.# Lithium carbonate is well absorbed orally. It is neither protein bound nor metabolized.# The kidney handles lithium in much the same way as sodium. Most of the filtered lithium is reabsorbed in the PCT. When Na+ is reabsorbed so is lithium.# It has narrow therapeutic window. Average half-life is 20-24 hours.# Renal clearance of lithium is l/5th of creatinine clearance.# On repeated medication steady state plasma concentration is achieved in 5-7 days.# This is higher in older patients & in those with renal insufficiency.# It is used in the treatment of- Acute mania,- - Headache (Vascular) - SIADH. --(Mnemonic: A HSBC)- Bipolar disorder (mainstay of Rx of acute mania+prophylaxis),- Cancer chemotherapy induced leucopenia (neutropenia)- Consensus Guidelines for Drug Treatment of Acute Mania and Bipolar Depression: ConditionPreferred Agents1Euphoric maniaLithium2Mixed/dysphoric maniaValproic acid3Mania with psychosisValproic acid with olanzapine, conventional antipsychotic, or risperidone4HypomaniaLithium, lamotrigine, or valproic acid alone5Severe depression with psychosisVenlafaxine, bupropion, or paroxetine plus lithium plus olanzapine, or risperidone; consider ECT6Severe depression without psychosisBupropion, paroxetine, sertraline, venlafaxine, or citalopram plus lithium7Miid to moderate depressionLithium or lamotrigine alone; add bupropion if needed