Example: Metronidazole is a drug used in the treatment of anaerobic infections. Its half-life is 8 hours, and Vd is 0.9 L/kg in children and in adults. Calculate the CLT and AUC after administration of a single oral dose of 500 mg to a child (25 kg), and to an adult (70 kg) if the bioavailability of this oral product is 90%.

a- In the child (25 kg)

CLT =

0.693

8 hr x 22.5L = 1.95 L/hr
AUC =

(0.9) 500mg

1.95 L/hr = 231 mg-hr/L
body weight (kg)
In this example the Vd is proportional to the body weight = 0.9 L/Kg. Because the half-life (and k) are similar in children and in adults this means that the CLT is also proportional to the body weight. CLT/Vd = k.

b- In the adult (70 kg)

CLT =

0.693

8 hr x 63L = 5.46 L/hr
AUC =

(0.9) 500mg

5.46 L/hr = 82.4 mg-hr/L
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