T20: C0 from AUC and K

50. Pharmacokinetics 50.1) PK Basic parameters 50.1.3) Area Under Curve (AUC) AUC basic concepts Normal 1

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159.5 mg of a drug (elimination rate constant 0.225 h-1) was administered to a patient as an IV push. The plasma concentration over the time (AUC) was found to be 13.91 mg × h/L. Calculate the initial plasma concentration after administration of the drug.

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lb equals 3.13 mg/L kg

    We know that, AUC may be calculated from dose (`X_{0}`) and clearance (`Cl`) OR initial concentration (`C_{0}`) and the elimination rate constant (`K`).

    ` AUC = (X_{0})/(Cl) = (C_{0})/K`.

    By rearranging the equation, we find:

    `C_{0}=AUC × K`

    `C_{0}=(13.91 \quad mg × h)/L × 0.225 \quad h^{-1} = 3.13 \quad (mg)/L`. Ans.