Phenytoin
Also known as: Hydantoin, Dilantin®
Use
Therapeutic monitoring of phenytoin levels for patients undergoing anticonvulsant therapy, measuring phenytoin (and phenobarbital when ordered as part of a panel) concentrations in serum to guide dosing and ensure therapeutic efficacy while avoiding toxicity.
Special Instructions
Collect serum in a plain red‑top tube (no gel separator). For trough levels: collect just prior to next dose; for patients on fosphenytoin, collect at least 2 hours after IV infusion or 4 hours after IM injection.
Limitations
Specimen types other than serum collected in a plain red‑top tube (e.g., gel separator tubes) may yield falsely low results due to lipophilic drug absorption; incomplete adherence to trough collection timing may misrepresent true steady‑state levels.
Methodology
Immunoassay
Biomarkers
Result Turnaround Time
3 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
Not provided
Minimum Volume
Not provided
Container
Red‑top tube (no gel)
Collection Instructions
Collect serum in a red‑top tube without gel; collect just prior to next dose; if on fosphenytoin, trough: ≥2 h after IV or ≥4 h after IM.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 5 days |
| Refrigerated | 7 days |
| Frozen | 30 days |
Other tests from different labs that may be relevant