Phenytoin
Commercial names and formulations:
Brand names: Dilantin, Phenytek
Formulations: Capsule, Dilantin Infatab chewable tablet, Dilantin oral suspension, Cerebryx (fosphenytoin) for intravenous or intramuscular use
Years on the market:
In the US since 1953
How to store it?
Store at room temperature and protect from moisture.
What does the body do to the medication?
Can I take it with food?
Yes
How long does it take to get to the blood after I take it?
2-3 hours on average in a healthy person, but greatly dependent on age and other medical conditions
How long does it take to start having a steady effect?
7-10 days on average in healthy person, but greatly dependent on age and other medical conditions
Can this medication be started at a high dose or it has to be started gradually?
Gradually in non-emergency settings, but it can be given quickly by mouth or vein in emergency situations
How long does it stay in the body?
Up to 1 day
How is it eliminated?
Liver
What does the medication do to the body?
Type of epilepsy that helps:
Partial Epilepsy
FDA approved for:
Partial seizures, with and without secondary generalization, and primarily generalized tonic-clonic seizures
Common side effects:
• Skin: mild or severe rash, redness, itching, burning
• Bones: osteoporosis (painless softening of the bones) over the long term
• Blood: low platelet count, decrease in white blood cells, decrease in red blood cells, anemia
• Liver: liver damage
• Kidneys: none
• Stomach and intestines: nausea, vomiting, constipation
• Heart: none typically by mouth. With intravenous use, low blood pressure and irregular heart rhythms are a potential risk
• Brain: nystagmus (uncontrolled eye movements), difficulty with coordination, slurred speech, confusion, dizziness, difficulty sleeping, twitching, tremor, headaches
• Mood: nervousness
• Others: coarsening of the facial features, enlargement of the lips, overgrowth of the gums, lymphoma
Serious side effects:
Severe allergic skin rash, severe liver damage, severe blood cell problems, lymphoma
Risk of suicidal thoughts or behavior
What happens if I get too much of it (intoxication)?
Symptoms include uncontrolled eye movements, difficulty with coordination and difficulty speaking. Other signs are tremor, lethargy, nausea, vomiting, and possibly coma and death.
What happens if I stop it suddenly (withdrawal)?
Abrupt withdrawal of phenytoin in patients with epilepsy may cause status epilepticus.
Who should not take this medication?
You should not take phenytoin is you know you are allergic to any of the ingredients, or if you have a generalized epilepsy, because it may worsen some seizure types such as absence and myoclonic seizures. Patients with a history of liver disease or past allergic reactions to medicines should also use this medication with caution. Patients with acute intermittent porphyria should not use this medication
What is the average dose and how many times a day should be given?
Children: 4-10 mg/kg/day (may be divided two or three times a day). Close monitoring of blood levels is especially recommended in premature and term infants.
Adults: 300 mg once a day, but for some patients, twice a day is needed. Depends also on if the immediate- or extended release formulations are used.
Does the body get used to the medication?
Yes
Medications to be careful with:
Other AEDs that may increase the blood level of Phenytoin:
Phenobarbital, Primidone, Carbamazepine, Diazepam, Valproic Acid, Topiramate, Felbamate, Oxcarbazepine, Zonisamide
Other AEDs that may decrease the blood level of Phenytoin:
Phenobarbital, Primidone, Carbamazepine, Diazepam, Valproic Acid, Vigabatrin
Other drug interactions:
Phenytoin will lower levels of felbamate, carbamazepine, lamotrigine, topiramate, tiagabine, zonisamide, lorazepam, and diazepam, and valproic acid.
Phenytoin levels are raised by isoniazid, cimetidine, chloramphenicol, dicumarol, sulfonamides. Phenytoin lowers warfarin and corticosteroids. Some antacids will impair absorption.
Blood work required?
CBC and CPM?
Phenytoin serum level determinations may be necessary for optimal dosage adjustments.
How often?
Varies greatly by age and presence of other medical issues. Usually monthly, then every three to six months
Are medication levels in blood useful?
Yes
Normal range
10-20 mcg/mL
Women’s health
Affects contraceptives?
Yes, will lower the effectiveness of oral conceptives
Affect fertility?
Yes, there have been reports linking phenytoin to infertility
Are safe in pregnancy?
There is a small, but real, increased risk of malformations such as cleft lip and palate and cardiac abnormalities. Should be used only under the guidance of a physician
Category
Pregnancy Category D
Can breastfeed?
Phenobarbital is passed through breast milk so it may or may not be safe to breast feed while taking Phenobarbital. The multiple benefits of breastfeeding need to be weighed against the probable small, but unknown, risks of the baby getting some limited amount of the medication. The baby needs to be watched closely for excessive sleepiness and poor feeding.
Affect bones (osteoporosis)?
Yes
Men’s health
Affects sexual performance?
Small risk of impotence
Affects fertility?
Associated with decreased sperm counts
Use other than epilepsy:
Used rarely for trigeminal neuralgia