T01-10) Random from these types

50. Pharmacokinetics 50.2) Plasma concentrations over time 50.2.1) Plasma concentrations over time

T01: Later plasma concentration Normal 1


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For an intravenously administered drug, if the concentration at 3 hr is 2.34 mg/mL, and concentration at 11.6 hr is 0.285 mg/mL, then determine the elimination half life of the drug. Assume that the drug follows a first order kinetics.


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lb equals 2.83 h kg

    For a first order process,
    `C_{t}=C_{0}×e^(-kt)`
    It may be re-organized as:
    `ln(C_{t})=ln(C_{0})-kt`
    `∴ k = ln(C_{0}/C_{t})/t`
    Difference between two time points (11.6 hr and 3 hr) is 8.6 hr.
    `\implies k =(ln(2.34/0.285))/8.6`
    Or, `k = 0.245`
    Thus, the rate constant is `0.245 \quad h^{-1}`.
    Now, to calculate the half life from rate constant: `t_{1/2}=0.693/k=0.693/(0.245 \quad h^(-1))=2.83 \quad h` (Ans).