How many hours should the physician withhold lithium in order to reach a safer, yet likely therapeutic level of 0.75 mEq/L?
A 46-year-old man complained to his physician of a fine hand tremor, diarrhea and frequent need to urinate. The man had been receiving lithium therapy for one month because of a bipolar disorder. Routine lab test showed a normal renal function and a plasma lithium level of 3 mEq/L. Lithium has a volume of distribution of about 45 L and a half-life of about 20 hours.
Learning objective: calculate the time to withhold Li+ therapy in case of Li+ overdose
By definition the plasma concentration of a drug halves every half-life. Therefore the Plasma
level will be 1.5 mEq/L after one half-life and 0.75 mEq/L after 2 half-lives, i.e after 40 hours.
A, B, C, D, E) (see explanation above)