The Leeds Teaching Hospitals NHS Trust

Phenytoin

Phenytoin

Anti-convulsant. Phenytoin is strongly bound to albumin and plasma concentrations should be interpreted in the light of plasma albumin.

Tube 01 (SE) - Serum Gel
ID Tests&Tubes0091
Additional Information For monitoring purposes blood should not be drawn before a steady state is attained. This will not be achieved for at least 7 days after starting therapy or changing dose. In children, this period is slightly shorter at 5 days. Small changes in dose can also affect serum levels. PHARMACOKINETICS: Phenytoin is an anti epileptic drug (note it is not effective for absence seizures). Its mechanism of action is modulated by Na,K ATPase which results in blockage of neurotransmitter release. Phenytoin is not readily soluble in aqueous solution and if administered IV it tends to precipitate at the site of injection and is slowly absorbed. The oral absorption of phenytoin is also slow and sometime incomplete. However, once absorbed the drug is highly protein bound (90 - 95%). The pharmacological effect of phenytoin is directly related to the amount of drug present in the free (unbound) state as only free phenytoin is able to cross biological membranes and interact with the biologically important binding site. Side effects of therapy include nausea, vomiting, ataxia, slurred speech. The hepatic metabolism of phenytoin can become saturated within the therapeutic range. Once saturated small dosage increments can result in large changes in blood concentration. The toxic effects of phenytoin include seizures, impaired consciousness and hypotension.
Turn Around A&E: N/A
Day Case: 24 Hours
In-Patient: 24 Hours
Out-Patient: N/A
GP: N/A
Send to Blood Sciences LGI
Contact For further details please contact Leeds Pathology customer services: leedsth-tr.pathologycustomerservice@nhs.net.
Collection Con Intensive care units, renal unit, transplant unit, patients on IV heparin use lithium-heparin (Green with Yellow ring) tube.
Instructions for Lab Staff: Standard lab processing - No special requirements.
Sample REQ Blood
Ref. Range Notes Blood Sciences Refernce ranges available through the useful information and links page:
https://www.leedsth.nhs.uk/a-z-of-services/pathology/blood-sciences/useful-information-and-links/
Units mg/L
Telepath PHENY2L