Phenytoin dosing:
(conc desired - conc. actual x 0.7 x wt in kg )divided 0.92 = dose in mg
or 15 - 20 mg/kg = dose in mg.
e.g: John Doe is 51-yo admitted for TBI. Decision made to start phenytoin for antiseizure prophylaxis. Pt. weighs 70 kg.
Dose = C (goal conc) x V (volume distribution) x wt in Kg/S (salt factor) x F (bioavailability)
Dose - 20 mcg/mL x 0.7L/kg x 70 kg/0.92 x 1 = 1065 or ~1000 mg.