Phenytoin is a drug to  control seizures in people with epilepsy. This medication is also used to treat trigeminal neuralgia, as well as prevent and treat seizures that occur during or after neurosurgical procedures.

Phenytoin or phenytoin belongs to the class of anticonvulsants. This drug works by reducing excessive electrical activity in the brain so that seizures can subside. Phenytoin is available as capsules, slow-release capsules, and injections that must be used with a doctor's prescription.

Phenytoin trademarks:  Curelepz, Decatona, Dilantin, Dextoin, Ikaphen, Kutoin, Kutoin 100, Phenytoin Sodium, Phenitin, Phenytoin Sodium , Sanbetoin 

What is Phenytoin

class Prescription drug
Category Anticonvulsant
Benefit Preventing and treating seizures in epilepsy , and treating trigeminal neuralgia
Used by Adults and children
Phenytoin for pregnant and lactating women Category D: There is evidence that the ingredients pose a risk to the human fetus, but the benefits may outweigh the risks, for example in dealing with a life-threatening situation. Phenytoin can be absorbed into breast milk. If you are breastfeeding, do not use this medicine without consulting your doctor first.
Drug form Capsules, slow-release capsules and injectables

Warning Before Using Phenytoin

Phenytoin should not be used carelessly. Before using phenytoin, you need to pay attention to the following points:

  • Do not use phenytoin if you have an allergy to phenytoin or have had serious side effects from this drug. Tell your doctor any allergies you have.
  • Tell your doctor if you have or currently have heart disease, low blood pressure , liver disease, vitamin D deficiency , osteoporosis, osteomalacia , porphyria, hypothyroidism , kidney disease, hypoalbuminemia , lupus, diabetes, or megaloblastic anemia .
  • Tell your doctor if you have been or are experiencing depression or have suicidal ideation.
  • Tell your doctor if you have or have had a heart rhythm disorder , such as sinus bradycardia, 2nd or 3rd degree AV block, or Stokes-Adams syndrome, before using injectable phenytoin.
  • Do not immediately drive a vehicle or operate heavy machinery while taking phenytoin, because these drugs can cause drowsiness or dizziness.
  • Do not drink alcoholic beverages while taking phenytoin, because alcohol can decrease the effectiveness or cause serious side effects of phenytoin.
  • Tell your doctor about your drinking habits, especially if you are having a hard time reducing or stopping the habit.
  • Tell your doctor if you are pregnant, may become pregnant, planning a pregnancy, or are breastfeeding.
  • Tell your doctor if you are taking birth control pills to prevent pregnancy, because phenytoin can reduce the effectiveness of birth control pills. Consult your doctor about proper birth control while using phenytoin.
  • Tell your doctor if you are taking other medications, including supplements and herbal products, to avoid drug interactions.
  • Tell your doctor that you are taking phenytoin if you plan to have surgery or certain medical procedures during your treatment, including dental surgery.
  • See your doctor immediately if you experience an allergic drug reaction , more serious side effects, or an overdose, after using phenytoin.

Dosage and Rules for Using Phenytoin

The dose of phenytoin given by doctors can be different, depending on the age and condition of the patient. Below is a breakdown of phenytoin dosage by drug form:

Capsule shape

Purpose: Epilepsy and seizures related to neurosurgery

  • Adult: 3–4 mg/kg or 150–300 mg daily, given as a single dose or in divided doses. Maintenance dose: 200–500 mg daily.
  • Children: initial dose of 5 mg/kg per day divided into 2 doses. The maintenance dose is 4–8 mg/kg per day, given in divided doses. The maximum dose is 300 mg per day

Condition: Trigeminal neuralgia

  • Adults: 300–500 daily in 1–2 divided doses.

Slow release capsule form

Condition: Seizures

  • Adult: initial dose of 100 mg, 3 times daily. Maintenance dose 100 mg 3–4 times daily. If needed, the dose may be increased to 200 mg, 3 times daily.

Intravenous (through a vein/IV) injection form

Condition: Status epilepticus or persistent seizures

  • Adult: 10–15 mg/kg given by slow injection or at a rate of not more than 50 mg per minute. Maintenance dose 100 mg every 6–8 hours, which may be given by mouth or by injection.
  • Children: 15–20 mg/kgBW given by IV infusion at a rate of 1–3 mg/kgBW per minute.

How to Use Phenytoin Properly

Injectable phenytoin should only be given by a doctor or medical officer under the supervision of a doctor.

Follow the doctor's recommendations and read the information printed on the package if you are given phenytoin in oral form. Do not add or reduce your dose without consulting your doctor first.

Take phenytoin regularly at the same time each day. Phenytoin capsules should be taken with food. Meanwhile, phenytoin capsules slow release can be consumed before or after meals.

Swallow the phenytoin slow-release capsules whole with plain water, without splitting, chewing, or crushing the capsules first.

If you forget to take phenytoin, take this medicine immediately if it is not close to the schedule for taking the next drug. If it is close, ignore the missed dose and do not double the dose at the next consumption schedule.

Do not stop taking phenytoin suddenly even if you have no complaints or have not had a seizure for a long time. Abruptly stopping can increase the number of seizures.

Please note, long-term use of phenytoin in patients with chronic epilepsy can increase the risk of decreased bone density. This is because phenytoin has the risk of reducing vitamin D from the body, causing low levels of calcium and phosphate in the blood and bones.

While undergoing treatment with phenytoin, you may be asked to have regular blood tests to anticipate side effects and to monitor the effectiveness of the treatment. Make sure to carry out the control according to the schedule given by the doctor.

Store phenytoin at room temperature. Do not store the drug in a place exposed to direct sunlight, heat or humidity. Keep this drug out of reach of children.

Phenytoin Interactions with Other Drugs

There are several drug interactions that can occur when phenytoin is used with other drugs, such as:

  • Decreased effectiveness and increased risk of developing HIV viral immunity when used with non-nucleoside reverse transcriptase inhibitors (NNRTI) antiviral drugs , such as nevirapine
  • Increased levels and effects of phenytoin when used with salicylic acid, other anticonvulsant drugs, antifungal drugs, benzodiazepine drugs , disulfiram, antiarrhythmic drugs , methylphenidate, capecitabine, cimetidine, tacrolimus, omeprazole, or SSRI antidepressant drugs
  • Increased risk of side effects from phenytoin when used with certain antibiotics, such as chloramphenicol , isoniazid, co-trimoxazole , clarithromycin, and sulfonamides
  • Decreased levels or effectiveness of phenytoin when used with sucralfate , folic acid, ciprofloxacin , rifampicin, ritonavir, theophylline , or anticancer drugs, such as bleomycin, carboplatin, cisplatin , or doxorubicin
  • Decreased effectiveness of doxycycline, voriconazole , theophylline, muscle relaxants , methadone, tolbutamide, phenobarbital, digoxin, atorvastatin , antiviral drugs, such as indinavir or lopinavir
  • Increased risk of liver damage when used with methotrexate
  • Increased risk of bleeding and increased phenytoin levels when used with warfarin

Phenytoin Side Effects and Dangers

There are several side effects that can occur when using phenytoin, including:

  • Headache, dizziness, or vertigo
  • Nauseous
  • Vomit
  • Constipation
  • Drowsiness
  • Hard to sleep
  • nervousness
  • Swollen and bleeding gums

Call your doctor if the side effects above don't improve or get worse. Immediately see a doctor if an allergic drug reaction or serious side effects occur, such as:

  • Swelling, pain, or skin discoloration at the injection site
  • Slow heart rate and feeling as if you are going to pass out
  • Difficulty speaking or slurred speech
  • Confusion or hallucinations
  • Mood swings
  • Muscle twitches
  • Movement, balance, or coordination of the body is disturbed
  • Blurred vision
  • Abnormal eye movements
  • Tingling in hands or feet
  • Facial changes, such as swollen lips or the appearance of a butterfly-shaped rash around the nose or cheeks (a symptom of lupus )
  • Hair grows excessively
  • It's easy to feel thirsty
  • The frequency of urination increases
  • Easily tired
  • Bone or joint pain

Go to the emergency room immediately if you experience a drug allergic reaction or more serious side effects, such as:

  • Stevens-Johnson Syndrome reaction on the skin, in the form of red spots or blisters that can peel and spread throughout the body
  • Uncontrolled muscle movements
  • Liver disorders, characterized by persistent nausea or vomiting, jaundice , dark urine, or clay-colored stools
  • Bruises that keep getting bigger or bleeding that doesn't stop
  • Swollen lymph nodes
  • It's hard to breathe
  • Erections that last a long time in men, can even cause pain ( priapismus )
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