A 5-year-old boy is brought to the emergency room by his mother. One hour ago, he ingested an unknown quantity of one of her prescription medications. Serum testing shows the boy's drug level is 5 mg/dL. The drug is known to have a half life of 1 hour, a volume of distribution of 150 ml, a bioavailability of 50%, and follow first-order elimination kinetics. Which of the following doses did the boy ingest?

Question

Quizplus · Accepted Answer

The drug's volume of distribution (Vd) is 150 ml, and the serum concentration is 5 mg/dL, which is equivalent to 0.05 mg/ml. Using the formula: Dose = Vd x Concentration, the dose is 150 ml x 0.05 mg/ml = 7.5 mg. Considering the bioavailability of 50%, the ingested dose is 7.5 mg / 0.5 = 15 mg. However, since the drug has a half-life of 1 hour and the concentration measured is after 1 hour, the initial dose would have been double, i.e., 30 mg.

A 5-Year-Old Boy Is Brought to the Emergency Room by His