Step I pharma question

[firstaid2012]

At 6hr after IV administration of bolus dose, the plasma level of a drug is 5mg/L. If the vd=10L and the elimination half life=3h, what is dose administered.

a. 100mg
b. 150mg
c. 180mg
d. 200mg
e. 540mg

please explain answer

 

[Phloston]

At 6hr after IV administration of bolus dose, the plasma level of a drug is 5mg/L. If the vd=10L and the elimination half life=3h, what is dose administered.

a. 100mg
b. 150mg
c. 180mg
d. 200mg
e. 540mg

please explain answer

Vd = (dose x bioavailability) / plasma concentration

10 L x 5 mg/L x 1 (IV always has F = 1) = dose = 50 mg = amount in the blood after two half-lives

So 50 --> 100 --> 200 mg = initial dose = choice D