Phenytoin Side Effects

Phenytoin can cause both common and serious side effects, some requiring immediate medical attention.^[1]

Common side effects may include:

• Drowsiness or sleepiness
• Confusion
• Slurred speech
• Uncontrollable or abnormal eye movements (nystagmus)
• Problems with balance, coordination, or muscle movement (ataxia)
• Dizziness

These effects are usually dose-related and may improve with adjustments or over time.^[1][2][4][6]

Serious side effects can occur and need prompt medical attention:

• Severe skin reactions, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), which may begin with flu-like symptoms followed by a red or purple rash that spreads and blisters.^{[1][2][3][4][5]}
• Allergic reactions such as hives, swelling of the face, throat, tongue, or difficulty breathing, which can indicate anaphylaxis.^[1][3]
• Bruising or unusual bleeding, which could signal a blood disorder.^[1][3][5]
• Mood or behavior changes, new or worsening depression, anxiety, or suicidal thoughts.^[1][2][4]
• Liver problems, including loss of appetite, abdominal pain, dark urine, pale stools, or yellowing of the skin or eyes.^[1][2][5]
• Fever, swollen glands, muscle aches, or unusual tiredness – signs of multi-organ hypersensitivity or immune reactions.^[1][2][3][5]
• Slow or irregular heartbeat, chest pain, dizziness, or fainting sensations.^[1][5]

If you experience any signs of serious side effects, seek emergency medical help immediately. Not all side effects are listed here; contact your healthcare provider with any new or concerning symptoms.^[1][2]

References

• [1] Phenytoin: Uses, Dosage, Side Effects, Warnings – Drugs.com
• [2] Phenytoin – Uses and Side Effects – Epilepsy Medication | CURE Epilepsy
• [3] Side effects of phenytoin – NHS
• [4] Phenytoin (Dilantin, Phenytek): Uses, Side Effects – WebMD
• [5] Phenytoin (oral route) – Mayo Clinic
• [6] 9 Common and Rare Phenytoin Side Effects – GoodRx