T02) Find Ct from C0, t-half and t
50. Pharmacokinetics 50.2) Plasma concentrations over time 50.2.1) Plasma concentrations over time
T01: Later plasma concentration Normal 1
Total tried: Correct: Wrong:
A 140 Kg patient was intravenously administered a drug. The plasma concentration was found to be 0.23 mg/L, when the blood was first collected. If the drug follows a first order elimination and the plasma half-life of the drug is `6.08 \quad h`, then determine the plasma concentration after 3.9 hours.
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lb equals 0.147 mg/L kg
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For a first order process,
`C_{t}=C_{0}×e^(-kt)`
In the question, k is not provided, but we can derive it from the equation below:
`k=0.693/t_{½}=0.693/(6.08 h)=0.114 h^{-1}`.
Plugging the values in this equation, we get:
`C_{t}=0.23 × e^(- 0.114 × 3.9)`
`∴ C_{t}=0.147`
Thus, the later concentration is: 0.147 mg/L. (Ans).