Use a half-life of 4 hours to determine the amount of a drug left in the body at 2 p.m.if a dose of 200 mg was administered intravenously at 6 a.m.

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The half-life of a drug is the time required for the blood or plasma concentration of the drug to fall to half of its original level. The number of hours that have elapsed between 6 a.m. and 2 p.m. is 8 hours. The half-life of the drug is 4 hours; this implies that two half-lives have elapsed since the administration of the drug. The amount of the drug remaining at 2 p.m. is 25 percent of its initial dose (25% F1F1F1S1F1F1F10 200 mg = 50 mg).

Use a Half-Life of 4 Hours to Determine the Amount