<prompt> A patient comes 6 hours after consuming morphine and presents with pin point pupils and respiratory depression. T 12 of morphine is 3 hours and volume of distribution Vd is 200 L. Current plasma concentration of morphine is 0.5 mgL. Calculate the initial morphine dose consumed by the person.100 mg400 mg10 mg50 mg  <response>: Volume of distribution means how much amount of plasma is required to accommodate the whole drug, if the plasma concentration remains constant. Current plasma concentration is 0.5 mgL means 1 litre contains 0.5 mg of morphine So, Vd of 200 L means 200 litre contain 0.5 x 200100 mg So now total amount of morphine present in the body is 100 mg. This is the amount present in body after 2 half lives half life is 3 hours and patient presented after 6 hours T12 3 hrsAfter 1 t12 drug remaining in body is 50 of initial. After 2 t12 drug remaining in body is 25 of initial If initial amount of morphine in body is x mg so, 100 25 of x S0, x 400 mg So the drug present in body initially is 400 mg 