T09: Clearance from plasma half-life and volume of distribution.

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 3.69 h. It is administered as an IV bolus to a 146 Kg patient. If the volume of distribution of the drug is 0.39 L/Kg, then calculate the clearance of the drug in this patient's body.

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lb equals 10.705 L/h kg

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/(3.69 h)= 0.188 \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 = 0.39 \quad L/(Kg) × 146 \quad Kg =56.94 \quad L.

Plugging the values in the first equation we get:
 Cl = 0.188 \quad h^{-1} × 56.94 \quad L = 10.7 \quad L/h  Ans.

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