Predicting individual phenytoin serum levels of patients seen in a private office practice.

We evaluated the practicality of predicting phenytoin serum levels in an office practice. Once two phenytoin serum levels were obtained on two different dosage regimens, a table of future doses and predicted serum levels was calculated and plotted on a graph. Subsequent dosage adjustments resulted in serum levels that correlated well with predictions. In 7 of 10 patients, the predicted serum levels were within 2 micrograms per milliliter of the actual values. To improve compliance, the plot was used as a visual aid in patient education.