Question

For a drug that has an initial plasma concentration of 120 mg/L and a half-life of 3 hours, what would the plasma concentration be 12 hours after the initial concentration of the drug elimination is following first order elimination?

Answer 1

7.5 mg/L

Step-by-step explanation:

As the drug elimination is following the first order of reaction mechanism so for such reactions the following equation relates the final and initial amount

`\text {Final amount} = \text {initial amount}((1)/(2) )^{\frac{t}{\text {half life}} }`

The values given in the question are

Initial concentration = 120 mg/L

Half life = 3 hours.

Time = 12 hours

Thus, putting the given values in the above equation, we get

`\text {Final amount}= 120((1)/(2) )^{(12)/(3) }`
`= 120((1)/(2) )^(4 ) = (120)/(16) = 7.5`

Thus, after 12 hours the concentration of the remaining drug will be 7.5 mg/L.