Download Antiepileptic Medication: Phenytoin (Dilantin)

Antiepileptic Medication:
Phenytoin (Dilantin)
▬ Loss of calcium in bones (chronic
therapy)
▬ Gum overgrowth (10-40%)
▬ Decreased red and white blood cells
▬ Lymph node enlargement
General Information
Phenytoin was approved in 1938 for treatment of
partial or generalized seizures. It is frequently given
to treat status epilepticus.
How does it work?
Phenytoin helps to prevent seizures by blocking
sodium channels and sometimes calcium channels.
This slows down the release of excitatory
neurotransmitters.
•
Available forms
This drug is also offered as a generic medication. It
can be given intravenously with certain precautions.
It is available in the following doses.
•
Drug basics
It is absorbed through the intestinal wall. Taking it
with food can change how well it is absorbed. About
70 to 90% of the drug will bind to proteins in the
bloodstream. This part of the drug is inactive.
After you take your dose, it takes about 4 to 12 hours
for the drug to have a maximum effect. You might
be more aware of dose related side effects at this time
if you have them. It takes about 7 to 42 hours for
half of the drug to be removed from your body. It is
metabolized by enzymes in the liver and excreted in
the urine. Once these enzymes are full, the amount
of free phenytoin increases very quickly. This can
lead to dose dependent side effects.
Phenytoin has been used in pregnancy and is a
category D risk. It has an increased risk of facial
clefts, diaphragmatic hernias, congenital heart
abnormalities, and hip dysplasias. Babies born to
mothers taking phenytoin typically have wide-spaced
eyes, shorter fingers and deformed fingernails, and
developmental delay.
Side Effects
There are 3 different types of side effects.
• Drug specific:
▬ Painful rash on chest, back, lips, both
arms and legs (like a sun burn)
▬ Irreversible numbness and loss of reflexes
in legs (chronic therapy)
▬ Poor balance from cerebellar atrophy
(chronic therapy)
Dose-related (phenytoin intoxication):
▬ Difficulty walking
▬ Drowsiness and confusion
▬ Tiredness
▬ Slurred speech
Initiation: You may notice some dose-related
side effects during the first couple of weeks of
treatment.
You need to report any signs of drug specific
reactions to the doctor immediately. You may be
asked to stop the medication.
•
•
•
•
Many Interactions
Phenytoin lowers many drug levels:
anticonvulsants, Coumadin, steroids,
theophylline, folate, furosemide,
cyclosporine, STATINS, oral contraceptives,
digoxin, methadone, and tricyclic
antidepressants.
Medications that increase phenytoin levels:
amoidorone, antifungal medications,
paroxitine, sertraline, propranolol, diazepam.
Medications that lower phenytoin levels:
antacids, theophylline, certain nutritional
formulas (Isocal), aspirin, dexamethasone,
methotrexate, and some antibiotics.
Dose may need to be reduced in kidney
failure.
Lab Monitoring
Frequent phenytoin levels are often necessary during
treatment. The free level is more important than the
total level. This is the amount of drug actively
working to stop seizures. Test results are usually
back the same day they are drawn.
Final Note
If you are having difficulty with you medication, please
notify your doctor. You dose may be able to be adjusted.
References
Created by Diana Murray RN, CNS, MS, CNRN
Providence Brain
Institute, Portland,
Oregon
Shorvon, S. (2005). Handbook of epilepsy treatment, 2nd ed. Malden, MA:
Blackwell publishing: