Test Detail
Overview
Interpreting Results
FAQ's

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Written by
Dr. Betina Chandolia
BDS, MDS - Oral Pathology and Microbiology
Reviewed by
Dr. Ashish Ranjan
MBBS, MD (Pharmacology)
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Phenytoin

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Phenytoin
You need to provide
Blood
This test is for
Male, Female
Test Preparation
  1. No special preparation required

Overview


What is Phenytoin?

Phenytoin is a drug used in the treatment of seizures as in epilepsy, complex partial seizures, and seizures that occur during or after a neurosurgical procedure. The Phenytoin Test is performed to measure the levels of phenytoin in blood.


Why is Phenytoin done?

The Phenytoin Test is performed:

·         To establish the therapeutic dosage for phenytoin in the blood

·         To monitor phenytoin levels at regular intervals to maintain therapeutic concentration after starting treatment

·         To check for phenytoin toxicity, if toxicity symptoms appear

What does Phenytoin Measure?

The Phenytoin Test measures the levels of phenytoin in blood.

Phenytoin is a drug used mainly for the treatment of epileptic seizures. It is also used to treat convulsions and seizures caused due to neurosurgery. It may be prescribed along with other anticonvulsant medications like phenobarbital. Phenytoin, taken orally is absorbed in the intestinal tract and goes into the blood. In blood, most of it gets bound to plasma proteins like albumin and only a small portion remains free. Only the free phenytoin remains metabolically active and the phenytoin-protein complex remains inactive. Phenytoin blocks the excessive electrical conductivity between the neurons in the brain during seizures.

Phenytoin levels are affected by a number of factors including liver function, other drugs, levels of plasma proteins that form complex with it, and the age of the patient. Since phenytoin levels need to be maintained within a very narrow therapeutic range in blood, they are monitored regularly during treatment.

Interpreting Phenytoin results


Interpretations

Therapeutic Range:

Total phenytoin:

10 to 20 µg/ml (Children and adults)

8 to 15 µg/ml (Newborns)

Free phenytoin: 1 to 2 µg/ml

The therapeutic range of phenytoin may vary from person to person and depends on a number of other factors. Hence, the therapeutic range is established for the patient at the beginning of treatment.

Lower than the therapeutic range phenytoin concentration makes the drug ineffective in treatment.

Higher than the therapeutic range phenytoin concentration induces symptoms associated with phenytoin toxicity.

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Phenytoin


Frequently Asked Questions about Phenytoin

Q. How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood from a blood vessel in your arm. The healthcare provider will tie an elastic band around your arm to make the blood vessels swell with blood. This makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You will feel a tiny pinprick during the procedure. Blood sample once collected will then be sent to the laboratory.
Q. Is there any risk associated with this test?
There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.
Q. Is there any preparation required before the test?
Inform the doctor about the medications you may be taking. No other specific preparations are usually required before this test.
Q. What is epilepsy?
Epilepsy refers to a group of medical conditions which are characterized by long-term risk of recurrent episodes of seizures ranging from a few seconds of unconsciousness to long periods of involuntary jerking and twitching. Epilepsy hinders the electrical impulse transmission and nerve activity regulation in the brain. Epilepsy may be caused due to genetic factors or brain injury due to stroke, trauma, etc. Seizures may be focal or partial with only one hemisphere of the brain affected, or generalized with both brain hemispheres affected. Epileptic seizures may occur as an isolated episode, occasional seizures, or frequently recurring episodes.
Q. What are the symptoms of Phenytoin toxicity?
Symptoms of Phenytoin toxicity include: · Swelling of gums · Swelling of lymph nodes · Fatigue · Nausea and vomiting · Hirsutism (male pattern body hair in females) · Fever · Insomnia · Confusion and irritability · Difficulty speaking or swallowing · Rashes · Involuntary eye movement (Nystagmus) · Abnormal heartbeat · Hypotension
Q. What are some common triggers of epileptic seizures?
Epileptic seizures can be triggered by a number of different stimuli. Common triggers include: · Bright flashing lights or patterns · Sleep deprivation · Stress · Particular time of day · Fever · Alcohol · Medical and non-medical drugs · Hormonal changes as in menstrual cycle · Malnutrition · Low blood sugar levels · Some types of food · Caffeine
Q. What factors can affect the Phenytoin test results?
The Phenytoin levels in blood can be affected by a number of factors including: · Age of the patient (phenytoin is metabolized faster in children than in adults) · Liver disease · Blood protein concentrations · Other anticonvulsant drugs · Other drugs like aspirin, estrogen etc. · Alcohol
Q. When are free phenytoin levels checked?
Most of the phenytoin in blood is complexed with blood proteins and remains inactive, and only a small portion remains free and metabolically active. The blood Phenytoin test measures the total phenytoin levels in blood since the bound and free phenytoin maintain a balance under normal circumstances. Free phenytoin levels may increase in blood with respect to total phenytoin in cases of: · Liver diseases · Kidney failure · Hypoalbuminemia (low blood albumin levels) · Certain medications like aspirin, naproxen, ibuprofen, etc.
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