Wednesday April 5, 2006
How much extra phenytoin
The formula to decide, how much extra phenytoin should be prescribed to get level therapeutic is
Extra phenytoin needed = [0.7 x IBW x (15 - current level) ] / 0.92
Where IBW = Ideal body weight (note - this is 'ideal' body weight)
e.g: If patient with ideal body weight of 62 kg has dilantin level of 7.4, the extra required dose would be [0.7 x 62 x (15 - 7.4)] / .92 = 330 mg or to be practical about 300 mg.
Remember this formula is for patient with normal albumin and conserve renal function. Please see pearl from yesterday for phenytoin adjustment with low albumin and low CrCl here
Phenytoin dosing guidelines by D.McAuley, GlobalRPh Inc.