Question

8. A 30-year-old man is brought to the emergency department in a deep coma. Respiration is severely depressed and he has pinpoint pupils. His friends state that he self-administered a

large dose of morphine 6 h earlier. An immediate blood analysis shows a morphine blood level of 0.25 mg/L. Assuming that the Vd of morphine in this patient is 200 L and the half-life is

3 h, how much morphine did the patient inject 6 h earlier?

(A) 25 mg

(B) 50 mg

(C) 100 mg

(D) 200 mg

(E) Not enough data to predict

Answer 1

Intravenous kinetics of Morphine follow first order kinetic. We have Volume of distribution(Vd) =200 L, Half Life(t(1/2))=3 hours, t(final)=6 hours Concentration of morphine after 6 hours(C)= 0.25 mg/L.

According to first order kinetics: C=Co.e^(-kt).

k=0.693/t(1/2) = 0.693/3= 0.231

k*t=0.231*6= 1.356.

e^(1.356)= 3.88063966~4.

Co=C*e^(kt)= 1 mg/ml.

Initial amount of drug is = Co*Vd =1*200 = 200 mg.

So the correct option is D.