<prompt> A patient reaches a steady state level of lithium that produces toxic side effects. If he decides to discontinue his medication, how long would it take for his lithium blood levels to reach 25 of his original steady state levels assuming a half life of 22 hours for lithium?11 hours22 hours33 hours44 hours  <response>: Lithium, like most drugs follows first-order kinetics, which means a constant percent of the drug is eliminated per unit time. His drug levels will decrease by 50 every half-life. Therefore, they will be 50 of original levels after one half-life, 25 after two half-lives, 12.5 after three half-lives, etc. Two half-lives is 22 x 2 44 hours. Ref: Buxton I.L., Benet L.Z. 2011. Chapter 2. Pharmacokinetics: The Dynamics of Drug Absorption, Distribution, Metabolism, and Elimination. In L.L. Brunton, B.A. Chabner, B.C. Knollmann Eds, Goodman Gilmans The Pharmacological Basis of Therapeutics, 12e. 