Phenytoin level

Keywords: Dilantin level


5 mL blood in plain tube.

Method:Chromatography, immunoassay.
Therapeutic Interval:

40-80 µmol/L (10-20 mg/L).


Therapeutic drug monitoring.


Steady state is not achieved for several days. Re-testing after a change of dose should be delayed for 48 h.

The half-life is 7-60 h (dose dependent).

This drug exhibits Michaelis-Menten kinetics, that is, as serum levels rise a stage is reached when a small increase in dose causes a large increase in serum levels.


Glauser TA and Pippenger CE. Epilepsia. 2000; 41(8): 6-15.