Phenytoin, plasma or serum

Alternate test name

Dilantin, Diphenylhydantoin

Lab area

Clinical Biochemistry - TDM & Toxicology

Method and equipment

Equipment : Roche Cobas Pro c503

Method : The assay is based on the kinetic interaction of microparticles in a solution (KIMS). Phenytoin antibody is covalently coupled to microparticles and the
drug derivative is linked to a macromolecule. The kinetic interaction of microparticles in solutions, photometrically detected by turbidity measurements is induced by binding of drug‑conjugate to the antibody on the microparticles and is inhibited by the presence of phenytoin in the sample. A competitive reaction takes place between the drug conjugate and phenytoin in the serum sample for binding to the phenytoin antibody on the microparticles. The resulting turbidity is indirectly proportional to the amount of drug present in the sample.

Expected turn-around time

STAT/ Urgent/ Routine: 3 hours

Specimen type

Serum, Plasma Lithium Heparin

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

Canada

M5G 1X8

Phone: 416-813-7200

Toll Free: 1-855-381-3212

Hours: 7 days/week, 24 hours/day

Requisition

Phenytoin, plasma or serum - requisition

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

Anticonvulsant