T11: Mixed problems from T7 - T11.

50. Pharmacokinetics 50.1) PK Basic parameters 50.1.2) Clearance

50.1.2.1) Clearance basic concepts Normal 1


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135.33 mg of a drug was administered to a patient as an IV push, which resulted the plasma concentration of 3.81 mg/L. The plasma half life of the drug is 2.7 h. Determine the clearance of the drug in this patient.


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lb equals 9.129 L/h kg

    We know that, clearance (Cl) is the product of elimination rate constant (K) and volume of distribution (V).

    ` Cl = K × V `.

    In this case, we hav the dose of the drug administered (`X_{0}`) and the plasma concentration (`C_{0}`). We know that:
    `C_{0} = X_{0}/V ⇒ V = X_{0}/C_{0}`.

    From the relationship of `t_{½}=0.693/K`, we can calculate K as `0.693/t_{½}=0.693/(2.7 h)= 0.257 \quad h^{-1}`.

    Therefore, clearance (Cl) will be:
    `Cl = 0.257 \quad h^{-1} \quad × (135.33 \quad mg)/(3.81 \quad (mg)/L) = 9.13 \quad L/h`. Ans


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