J Korean Neurol Assoc.  1996 Jun;14(2):440-447.

The Clinical Study on the Predictability of Time from Toxic Level to Therapeutic Concentration on Phenytoin Toxicity

• Park HM
• Lee YJ
• Kim HT
• Kim SH
• Kim JH
• Kim MH
• Moon TS
• Shin DJ
• Jang IJ
• Shin SG

Abstract

It is important to predict time to reach therapeutic concentration in phenytoin toxicity. In tradition, frequent drug monitoring is inevitable until the therapeutic serum level is reached. A method of estimating Vmax and Vd of phenytoin with application to estimating time to reach therapeutic concentration of phenytoin is described. We evaluated the usefulness of that method in twelve patients with phenytoin toxicity whose initial levels ranging from 27.7 to 74.0 ug/ml. We compaired the observed time defined as the time of returning from the initial toxic level to the optimum therapeutic level by serial measurement of serum concentration with the calculated time by using the modified Michaelis-Menten equation (Km x In (C1/C2) +Cl-C2=Vmax/vd x T). We determined individual patient's Vmax (maximal metabolic rate of concentration), Vd(volume of distribution of concentration), and Km(constants of Michaelis-Menten equation) for phenytoin, using data obtained from two consecutive serum concentration and known value of Km in Korean. And then, we calculated the decline time of phenytoin. The calculated decline time did not differ significantly from observed decline time (P=0.830). It is possible to predict the time to the therapeutic range and to reduce the unnecessarily frequent drug monitoring.

MeSH Terms

Drug Monitoring
Humans
Phenytoin*
Phenytoin