Question

WS, an 8-year-old, 25-kg male, is receiving a 250-mg capsule of valproic acid (VA) q12h for the treatment of seizures. • The Cls of VA are 13 mL/kg/h for children and 8 mL/kg/h for adults. The V and F of VA are 0.14 L/kg and 1, respectively. The therapeutic plasma VA concentrations are 50–100 mg/L. The toxicity is observed as >200 mg/L. • WS has normal hepatic and renal functions. • (a) Predict the steady state trough concentration (Css,min) for WS, and • (b) comment on the adequacy of his current regimen, using a 1-compartment intravenous bolus model.

Answer 1

When dosage guidelines are not available for a drug, empirical dose adjustment methods are often used.

• Dosage normalized based on the child's age or body weight from adult drug dosages was used through the

Young's rule

[Adult Dose x (Age (Age + 12)) Child's Dose)

• and Clark's rule

• [Adult Dose x (Weight = 150) = Child's Dose), respectively.

In order to calculate Adj. BW, IBW needs to be calculated first,

• IBW = 45.5 + 2.3 x [Height (inches) - 60] kg

• Her IBW = 57 kg

Adj. BW = IBW + 0.4 x (TBW – IBW) kg Her Adj. BW = 97.8 kg

• Clcr (mL/min) = [(140-age) x (Weight in kg)]/[72 x serum creatinine] x 0.85

Her estimated Clcr = 87 mL/min