Phenytoin

ToxicologyAlso known as: 5,5-Diphenyl-2,4-imidazolidinedioneAlso known as: Diphenylhydantoinug/mL

Measures phenytoin (anti-seizure medication) concentration in serum or plasma.

Normal Range

Consult your provider

ug/mL

Abnormal Levels

Consult your provider

Specimen Type

Blood

Why This Biomarker Matters

Phenytoin monitoring helps ensure seizure medications are at therapeutic levels. Detecting low levels may indicate poor medication compliance, while high levels could signal toxicity risk.

Overview

Phenytoin (Dilantin) is an anti-seizure medication used to control epilepsy and other seizure disorders. This test measures phenytoin levels in urine to assess medication exposure and compliance. Urine phenytoin testing can help confirm medication use and provide information about drug metabolism, though blood levels are more commonly used for therapeutic drug monitoring. Abnormal levels may indicate poor medication adherence or altered metabolism.

Research & Evidence

17 publications

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Phenytoin as an emerging pollutant on non-target aquatic invertebrates: effects on.

Drug Chem Toxicol · 2026

PMID: 41521164Other

Clinical Mechanistic Insights Into Polymorphic Ventricular Tachycardia: Infection-Triggered Unmasking of Long QT Syndrome.

Am J Cardiol · 2026

PMID: 41554391Other

Refiningtreatment in women and men: protocol for an open-label randomised comparison of multi-dose oral metronidazole versus single-dose oral secnidazole.

BMJ Open · 2026

PMID: 42031495

Electrospun bi-layer carboxymethyl cellulose/polyvinyl alcohol/polycaprolactone nanofibers: fabrication, degradation, and phenytoin release kinetics.

Sci Rep · 2026

PMID: 41965368

Cannabidiol inhibits phenytoin clearance and can result in clinical changes: Two cases.

Seizure · 2026

PMID: 41764811

An update on the pharmacokinetic and pharmacodynamic interactions between antidepressants and antiseizure medications.

Expert Opin Drug Metab Toxicol · 2026

PMID: 41873592

1-Ethenyl-2-(methyl-sulfan-yl)-4,4-diphenyl-4,5-di-hydro-1-imidazol-5-one (Thio-phenytoin analogue): synthesis, structure and Hirshfeld surface analysis.

Acta Crystallogr E Crystallogr Commun · 2026

PMID: 41953337

Extracellular Vesicles as Xenobiotic-Metabolizing Enzyme Carriers: A New Paradigm for Brain Drug Metabolism.

Drug Metab Rev · 2026

PMID: 42060154

Different Effects of the Anticonvulsant Drugs Phenytoin and Phenobarbital on Forskolin-Induced BeWo Syncytialization.

Pharmazie · 2026

PMID: 42057681

Influence of hepatic steatosis on antiseizure drug metabolism: in vitro evidence from differentiated HepaRG cells.

Toxicol Lett · 2026

PMID: 41965184

Research data from MEDLINE/PubMed · 17 articles

Technical Information (LOINC Codes)

Standardized laboratory codes for this biomarker

3968-5Primary

Phenytoin [Mass/volume] in Serum or Plasma

ug/mL

17444-1

Phenytoin [Mass/volume] in Urine

ug/mL

35632-9

Phenytoin [Mass/volume] in Serum or Plasma by Screen method

ug/mL

3967-7

Phenytoin [Presence] in Serum or Plasma

14877-5

Phenytoin [Moles/volume] in Serum or Plasma

umol/L

4225-9

Phenytoin [Mass] of Dose

mg

12310-9

Phenytoin [Presence] in Urine

29224-3

Phenytoin [Mass/volume] in Body fluid

mg/L

14073-1

Phenytoin [Mass/volume] in Saliva (oral fluid)

ug/mL

43831-7

Phenytoin [Presence] in Specimen

Available Lab Tests

Order tests that measure this biomarker

phenytoin