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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The elimination half life of a drug is 5.25 h. It is administered as an IV bolus to a 130 Kg patient. If the volume of distribution of the drug is 0.67 L/Kg, then calculate the clearance of the drug in this patient's body.
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lb equals 11.497 L/h kg
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We know that, clearance (Cl) is the product of elimination rate constant (K) and volume of distribution (V).
` Cl = K × V `.
From the relationship of `t_{½}=0.693/K`, we can calculate K as `0.693/t_{½}=0.693/(5.25 h)= 0.132 \quad h^{-1}`.
Also, the total volume of distribution will be the product of volume per Kg body weight and the weight of the patient. Thus,
` V = 0.67 \quad L/(Kg) × 130 \quad Kg =87.1 \quad L`.
Plugging the values in the first equation we get:
` Cl = 0.132 \quad h^{-1} × 87.1 \quad L = 11.5 \quad L/h ` Ans