What is the Epanutin (Phenytoin) Test?

The Epanutin (phenytoin) test measures the concentration of phenytoin in the bloodstream. Phenytoin is an antiepileptic medication commonly used to control seizures and prevent abnormal electrical activity in the brain.

Because phenytoin has a narrow therapeutic range, small changes in dose can lead to sub-therapeutic levels or toxicity. Blood level monitoring is therefore essential to ensure the medication is effective while remaining safe.

This test is routinely used in patients receiving long-term phenytoin therapy or when dosing adjustments are required.

Why do I need a test for Epanutin (Phenytoin)?

You may need this test to confirm that your phenytoin level is within the therapeutic range. Levels that are too low may result in poor seizure control, while high levels can cause serious neurological and systemic side effects.

Monitoring is especially important after dose changes, when starting or stopping other medications, or if symptoms of toxicity or breakthrough seizures occur.

Symptoms and scenarios where testing is recommended:

• Epilepsy or seizure disorders
• Breakthrough seizures
• Suspected medication toxicity
• Dose adjustments or treatment changes
• Long-term antiepileptic therapy
• Drug interaction monitoring
• Liver dysfunction affecting drug metabolism
• Unexplained neurological symptoms

Benefits of the Epanutin (Phenytoin) Test

• Ensures effective seizure control
  Confirms therapeutic drug levels.
• Prevents medication toxicity
  Identifies dangerously high concentrations.
• Supports personalised dosing
  Accounts for individual metabolism differences.
• Monitors long-term antiepileptic therapy
  Essential for ongoing treatment safety.
• Detects drug interactions early
  Phenytoin levels are affected by many medications.
• Supports neurological symptom investigation
  Helps explain dizziness, confusion or coordination issues.
• Guides clinical treatment decisions
  Assists neurologists in dose optimisation.
• Established standard of care in epilepsy management
  Widely used and clinically validated.

Step-by-Step: How Testing Works

Choose your preferred testing method

You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.

Option 1 – In-Clinic Blood Draw

1. Select your nearest UK clinic and book an appointment.
2. A clinician or phlebotomist collects a venous blood sample.
3. The sample is analysed for Epanutin (phenytoin) concentration.
4. Results are delivered securely online.

Option 2 – Home or Hotel Phlebotomy (+£60)

1. Book a UK-wide home or hotel visit at a convenient time.
2. A trained phlebotomist collects your blood sample on-site.
3. The sample is transported to the laboratory.
4. Results are uploaded digitally without the need to travel.

Your Results Explained

Low Levels

Low phenytoin levels may result in inadequate seizure control.
This may require dose adjustment or assessment of compliance.
Typical UK therapeutic range: ~40–80 µmol/L (laboratory dependent).

Normal Levels

Levels within the therapeutic range suggest effective and safe dosing.
This supports stable seizure management.

High Levels

Elevated phenytoin levels increase the risk of toxicity.
Symptoms may include dizziness, unsteady gait, confusion, nausea and visual disturbances, and require prompt clinical review.