Equivalence of the Steady State Concentrations of Two Dosage Regimen of Phenytoin Using Computer Optimisation Programme OPT6

OPT 6 is an optimisation programme through which optimisation of various drugs like phenytoin can be done. It is based on Bayesian Statistical Theory and Maximum Likelihood Estimation. This study was aimed to determine the steady state concentration equivalence using the Optimisation programme OPT 6 to compare 300mg once daily phenytoin and 100mg tid phenytoin. Epileptic outpatients attending neurology department, were included. Twenty-four patients were enrolled into the study. Informed consent was taken. Liver and renal function was checked. Basal phenytoin levels were also estimated. Once preliminary tests were found to be normal the patients were randomised into one of the two treatment arms either 300mg once daily or 100mg thrice daily. Each arm was for a 2 week period. Peak and trough phenytoin concentrations were estimated. These results were entered into the optimisation programme along with demographic data for both regimens separately. Then the predicted steady state concentration was noted. Wilcoxon’s Signed Rank test was done to find the difference in the predicted steady state concentration. There was no significant difference between steady state concentration (Css) using trough values of both dosing regimens. There was significant difference between Css using trough and peak values for both dosing regimens. There was no significant difference between Css using peak values of both regimens. This study has illustrated trough value can be used for dose adjustment of patients on phenytoin once daily and thrice daily using OPT6 programme.