Phenytoin – serum
Last updated: Sunday, 21, March, 2004
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| Item | Process |
|---|---|
| Specimen | 5 mL blood in plain tube. |
| Method | Chromatography, immunoassay. |
| Therapeutic Interval | 40-80 µmol/L (10-20 mg/L). |
| Application | Therapeutic drug monitoring. |
| Interpretation | Steady state is not achieved for several days. Re-testing after a change of dose should be delayed for 48 hours. The half-life is 7-60 hours (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. |
| Reference | Glauser TA and Pippenger CE. Epilepsia. 2000; 41(8): 6-15. |