| Laboratory: | Clinical Biochemistry (AUTOMATED) | ||||
| Test Name: |
PHENYTOIN (Alternate Name(s): Dilantin, Diphenylhydantoin) - (P) and (S)
Test Code:
PYN
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| Clinical Information: |
Phenytoin has been used extensively for seizure control (generalized tonic-clonic, complex partial, and simple partial). It is frequently used in initial therapy and measured to evaluate toxicity or monitor therapeutic levels.
Patient preparation instructions: Phenytoin has a long half-life and the time of draw is inconsequential. However, for oral therapy monitoring, collection time should be consistent for a given patient. |
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| Collection Devices: |
Gel tubes are not acceptable.
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| Specimen Required: |
Plasma: 1.0 mL
Pediatric Plasma: 1.0 mL
For oral therapy, collection time should be consistent for a given patient. For IV therapy, collection must be at least 2 hours after end of dose. Do not draw blood from an IV line through which the drug has been administered as it can produce erroneous results and impact patient care. Centrifuge within 2 hours of collection. Specimen Stability: 4 days refrigerated, 3 months frozen |
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| Referral: |
Serum
Samples must be transferred to an aliquot tube and stored frozen if analysis will not be complete within 48 hours (#110-10-05 Serum / Plasma Separation Procedure & Transport). |
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| Requisition: | |||||
| Reference Values: |
Therapeutic:
0-4 weeks: 6-14 mg/L (24-56 µmol/L) ≥5 weeks: 10-20 mg/L (40-80 µmol/L) Toxic: >20 mg/L (>80 µmol/L) Method of Analysis: Kinetic Interaction Microparticles in Solution (KIMS) assay (Roche Cobas) Enzymatic (peroxidase) competitive immunoassay (Ortho Vitros)) |
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| Availability: |
Stat or Routine
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| See Also: | |||||
| More Information: |
Interpretation & Assay Interferences:
Half-life: 8-60 hours (dose dependent) Time to steady state: 2-13 days |