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Phenytoin, plasma or serum

Alternate test name

Dilantin, Diphenylhydantoin

Lab area
Clinical Biochemistry - TDM & Toxicology
Method and equipment
Abbott Architect ci-4100
Expected turn-around time
Stat/ Urgent/ Routine: 3 hours
Specimen type

Serum, Plasma (Heparin or Citrate)

Specimen requirements

150 uL

Storage and transportation

4°C (transport with a cool pack if possible)

Special requirements

Trough 0-60 min before next dose.

Shipping information
The Hospital for Sick Children
Rapid Response Laboratory
555 University Avenue, Room 3642
Toronto, ON
M5G 1X8
Phone: 416-813-7200
Toll Free: 1-855-381-3212
Hours: 7 days/week, 24 hours/day
Background and clinical significance

Phenytoin is one of the most widely prescribed drugs for the treatment of seizure disorders. It is considered one of the drugs of choice for generalized major motor and focal seizures. Strong correlation has been observed between serum levels and both therapeutic and toxic effects. The primary pathway for phenytoin elimination (90%) involves a metabolic conversion to 5(4-hydroxyphenyl)-5-phenylhydantoin (HPPH) which is a saturable process that could lead to toxic serum levels with a small increase in dosage. Phenytoin toxicity primarily affects the centrol nervous sytem. Chromic treatment may lead to hyperplasia of the gums, anemia and osteomalacia. Because both metabolism and clearance are highly variable among individuals, a close monitoring of serum levels is appropriate for virtually every patient undergoing phenytoin therapy.

Disease condition


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