Phenytoin Adverse Effects & Nursing Considerations

Welcome to another post. In this post, we’ll look at the side effects, dosage, uses, and guidelines of phenytoin. As a student and nurse, gaining knowledge about this drug as part of your medical education will be beneficial.

Phenytoin (Rx)

  • Brand and Other Names: Dilantin, Dilantin 125, and more.
  • Classes: Anticonvulsants, Hydantoins; Antidysrhythmics, Ib

Phenytoin, also known as Dilantin, is an antiseizure medication that is highly effective in preventing tonic-clonic and focal seizures. Although it is ineffective in treating absence seizures, it remains a popular medication choice for those with epilepsy.

Fosphenytoin, the intravenous form of the medication, is explicitly utilized for status epilepticus that has not improved with benzodiazepines, as well as certain heart arrhythmias and neuropathic pain. If you or someone you know suffers from seizures, it is essential to consult with a medical professional to discuss the best treatment options available.


The intravenous form of the medication typically takes effect 30 minutes and can be effective for up to 24 hours. Blood tests may be conducted to determine the correct dosage. Alternatively, it can also be taken orally. Blood concentrations can be measured to determine the optimal dose.

Medical uses

  • Tonic-clonic seizures: Used in the prophylactic management of tonic-clonic seizures with complex symptomatology when a 5–10 day course is necessary to produce anticonvulsant effects.
  • Focal seizures: Employed to prevent the emergence of focal seizures with complex symptomatology (including psychomotor and temporal lobe seizures) and autonomic symptoms.
  • Absence seizures: Not recommended for pure absence seizures due to its potential to increase seizure frequency; however, it can be used with other anticonvulsants for combined absence and tonic-clonic seizures.
  • Seizures during surgery: A 2018 meta-analysis indicated that early antiepileptic treatment with either phenytoin or phenobarbital reduced seizure risk in the first-week post neurosurgery for brain tumors.
  • Status epilepticus: Considered as a second-line option, after unsuccessful treatment with a benzodiazepine, due to its slow onset of action.

Regular Dose Range

  • For an adult- Regarding antiseizure effects in adults, standard treatment involves administering both a loading dose and a maintenance dose of phenytoin. The IV loading dose is typically 15-20mg/kg NTE 25-50mg/min, while the maintenance dosage for daily administration is 5-6mg/kg divided into 1-3 doses. This method quickly raises the patient’s drug levels to a therapeutic level.
  • Pediatric patients’ recommended- Daily dose is 4-8mg/kg divided into three doses. The IV loading dose in children is 10-15mg/kg, not to exceed 50mg/min.

Phenytoin is an excellent illustration of a dosage calculation problem requiring weight-based dosing with some added complexity in divided doses. Let us evaluate your dosage expertise by solving a quick sample question.

QuestionThe MD has ordered a loading dose of phenytoin PO for a patient who weighs 64 kg. How much of the drug should be administered?
The loading dose should be 960mg (15mg/kg X 64 kg). You may think, how does it? Please, read our dosage calculation post.

Adverse Effects Of Phenytoin

Phenytoin is known to have various side effects, ranging from mild and temporary to more severe and long-term.

Common adverse reactions include:

  • Drowsiness
  • Nausea/Vomiting
  • Diarrhea/Constipation
  • Blurred vision/Double vision
  • Ataxia
  • Slurred speech
  • Rashes/Hives
  • Headache
  • Dizziness/Lightheadedness
  • Weight gain

Less common adverse reactions include:

  • Leukopenia (decreased white blood cells)
  • Agranulocytosis (decreased white blood cells)
  • Gingival hyperplasia (enlargement of the gums)
  • Hirsutism (excessive body/facial hair growth)
  • Chronic thrombocytopenia (low platelet count)
  • Toxic epidermal necrolysis (severe skin reaction)
  • Stevens-Johnson syndrome (severe skin reaction)
  • Liver toxicity/Hepatitis
  • Nystagmus (involuntary eye movement)
  • Peripheral neuritis (nerve inflammation)
  • Hypocalcemia (low calcium levels)
  • Drug fever

It is important to note that these side effects can vary in severity and do not always indicate a severe medical condition. If you experience any of the above reactions, seek immediate medical attention.

Phenytoin Nursing Considerations

When administering phenytoin, nurses must consider the patient’s medical history, potential drug interactions, and any allergies. This medication should be used cautiously in those with a history of liver disease, renal impairment,, or cardiac conduction abnormalities. It is also essential to closely monitor patients for signs of toxicity.

In addition, it is essential to note that phenytoin should not be taken with alcohol or any other CNS depressants, as this can increase the potential for side effects and overdose.

Phenytoin Use Guidelines:

  • Take medication exactly as prescribed by your physician.
  • Do not change the amount of drug or the frequency of administration without consulting your doctor.
  • Do not discontinue the medication without consulting your physician, as this can lead to withdrawal symptoms.
  • Do not take more than prescribed; seek immediate medical attention if you experience an overdose.
  • Maintain regular blood tests to ensure that it has its intended therapeutic effect and not causing any additional side effects.
  • Inform your physician if you are pregnant, planning a pregnancy, or breastfeeding, as this medication has been known to cause congenital disabilities.
  • Be aware of potential interactions with other drugs; inform your healthcare provider about all medications, vitamins, and herbal supplements you are taking before starting phenytoin.
  • Do not drink alcohol while taking this medication.
  • Contact your doctor immediately if you experience any symptoms: confusion, slurred speech, dizziness, blurred vision or double vision, rash or hives, or extreme fatigue.
  • Notify your physician if you have had a significant change in weight since beginning phenytoin therapy, as dosage adjustments may be necessary.

Final Words

Phenytoin can be an effective anticonvulsant for certain types of seizures when taken as prescribed and monitored closely by a physician. However, it is essential to understand the potential side effects and take appropriate precautions when administering it to patients. Understanding the importance of proper dosing and patient education can help ensure the treatment is safe and effective.

If you have any questions about phenytoin, don’t hesitate to contact your healthcare provider.



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