Epanutin (Phenytoin)
Private Epanutin (Phenytoin) blood test in London for £85, measuring one therapeutic drug marker with results in around 1 business day.
Turnaround time
1 business day
Biomarkers count
1
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Overview of the Epanutin (Phenytoin)
The Epanutin (Phenytoin) blood test measures the concentration of phenytoin circulating in the blood.
Phenytoin is an anti-seizure medicine used in the management of selected forms of epilepsy and seizures.
Epanutin is one brand name for phenytoin.
The test contains 1 biomarker: Epanutin (Phenytoin).
Phenytoin has a relatively narrow therapeutic range and unusual non-linear pharmacokinetics.
This means that once the enzymes responsible for metabolism begin to become saturated, relatively small dose changes can sometimes produce disproportionately large changes in blood concentration.
Therapeutic drug monitoring can therefore be useful where seizure control changes, toxicity is suspected, adherence is uncertain or interacting medication has been started or stopped.
Phenytoin is highly bound to albumin.
Conditions that reduce protein binding, including low albumin, pregnancy, significant kidney dysfunction and some drug interactions, can alter the relationship between the measured total phenytoin concentration and the pharmacologically active free concentration.
For routine monitoring, a trough specimen collected immediately before the next scheduled dose is generally preferred.
Results should be interpreted alongside dose, sample timing, albumin, kidney and liver function, seizure control and clinical symptoms.
What Does the Epanutin (Phenytoin) Test Check?
This test measures 1 biomarker.
Epanutin (Phenytoin)
Measures total phenytoin concentration in blood to support assessment of therapeutic exposure, possible toxicity, treatment adherence and drug interactions.
Who May Benefit From the Epanutin (Phenytoin) Test?
This test may be useful for people already taking phenytoin where therapeutic drug monitoring is clinically appropriate.
People with changing seizure control - A phenytoin level may help determine whether drug exposure is contributing to breakthrough seizures.
People with possible phenytoin toxicity - Blood measurement can support assessment where neurological adverse effects develop.
People following a dose change - Repeat testing can help assess the resulting concentration once an appropriate interval has passed.
People starting or stopping an interacting medicine - Numerous drugs can alter phenytoin metabolism or protein binding.
People with suspected medication non-adherence - An unexpectedly low concentration may provide additional information.
People with significant liver disease - Hepatic metabolism is important for phenytoin clearance.
People with low albumin or kidney dysfunction - Total phenytoin may require more careful interpretation where protein binding is altered.
Pregnant patients taking phenytoin - Pregnancy can alter drug disposition and requires specialist medication monitoring.
Specialist-requested anti-epileptic drug monitoring - Testing can be arranged where a neurologist or prescribing clinician has requested a phenytoin level.
How to Prepare
Do not skip, increase, reduce or stop phenytoin solely to alter the blood-test result unless specifically instructed by your prescriber.
Abrupt discontinuation can increase seizure risk.
Symptoms and Reasons to Consider the Epanutin (Phenytoin) Test
Possible phenytoin toxicity often produces neurological symptoms.
Unsteadiness or poor coordination - Ataxia is a recognised feature of excessive phenytoin exposure.
Nystagmus or abnormal eye movements - Higher concentrations can affect ocular motor control.
Double or blurred vision - Visual disturbance can occur with toxicity.
Marked drowsiness - Excessive exposure can impair alertness.
Slurred speech - Neurological toxicity can affect speech.
Confusion - More significant toxicity can affect cognition and consciousness.
Breakthrough seizures - Reduced exposure, missed doses or other factors may result in inadequate seizure control.
Symptoms after a recent dose adjustment - New neurological effects may prompt reassessment of the concentration.
Symptoms should not be interpreted solely from the phenytoin level because individual sensitivity varies.
A concentration within the usual therapeutic interval does not guarantee absence of side effects, and some people may remain clinically controlled at concentrations outside a standard range.
Severe confusion, collapse, repeated seizures, significantly reduced consciousness or rapidly worsening neurological symptoms require urgent medical assessment.
How to Book Your Epanutin (Phenytoin) Test
Booking your Epanutin (Phenytoin) test with London Blood Tests is straightforward.
Choose the Epanutin (Phenytoin)
Select the test online and review the therapeutic drug-monitoring information.
Select your sample collection option
Choose an in-clinic blood draw (+£35) or a home or hotel phlebotomy visit (+£60).
Attend your appointment
A trained professional collects the blood sample at the clinically appropriate time relative to your dose.
Laboratory analysis
Your sample is analysed for total phenytoin concentration.
Receive your results securely
Your authorised laboratory result is delivered securely by email for review with your prescribing clinician.
When Will I Receive My Results?
The expected turnaround time for the Epanutin (Phenytoin) test is approximately 1 business day after your sample arrives at the laboratory.
Additional analysis may occasionally extend reporting.
Understanding Your Results
A commonly used therapeutic interval for total phenytoin is approximately 10–20 mg/L, equivalent to around 40–80 micromol/L, although laboratory ranges and individual therapeutic targets can vary.
Lower concentrations may indicate inadequate exposure, missed doses, rapid metabolism or drug interactions.
Higher concentrations increase the likelihood of dose-related neurological toxicity.
However, total phenytoin can be misleading when albumin is low or protein binding is altered.
In these situations, an adjusted calculation or direct free-phenytoin measurement may sometimes be more informative.
Because phenytoin metabolism is non-linear, treatment changes require particular care.
Do not change the dose solely from a laboratory number. Results should be reviewed with the clinician responsible for prescribing your anti-seizure medication.
Why Book With London Blood Tests?
Private phenytoin monitoring in London - Access targeted anti-epileptic therapeutic drug monitoring.
Useful for dose assessment - Provides information about circulating phenytoin exposure.
Relevant to toxicity investigation - Blood measurement can support assessment where neurological adverse effects occur.
Relevant to changing seizure control - Testing can provide additional information where treatment effectiveness changes.
Fast laboratory turnaround - Results are expected approximately 1 business day after laboratory receipt.
Clinic and home visit options - Professional phlebotomy can be arranged according to dose timing.
Secure results by email - Receive your authorised report securely.
Clear pricing before booking - The Epanutin (Phenytoin) test costs £85.
Private Epanutin (Phenytoin) Blood Test in London
London Blood Tests provides the Epanutin (Phenytoin) blood test in London for people requiring therapeutic monitoring while taking phenytoin.
The test costs £85 and measures one biomarker: Epanutin (Phenytoin).
For routine monitoring, consistent trough sampling immediately before the next scheduled dose usually provides the most comparable results.
Treatment decisions should remain with the clinician responsible for prescribing phenytoin.