Medicine & USMLE

Phenytoin

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Neuro Drugs
  1. Levodopa, Carbidopa
  2. Levetiracetam
  3. Valproic Acid
  4. Anticholinergic Syndrome
  5. Cholinergic Crisis
  6. Benztropine / Trihexyphenidyl
  7. Lidocaine
  8. Pyridostigmine, Neostigmine, Edrophonium
  9. Naltrexone
  10. Pregabalin
  11. Scopolamine
  12. Phenytoin
  13. Ethosuximide
  14. Succinylcholine
  15. Opioids
  16. Memantine
  17. Halothane / Flurane
  18. Donepezil
  19. Propofol
  20. Ergotamine
  21. Triptans
  22. Selegiline / Rasagiline
  23. Entacapone / Tolcapone
  24. Gabapentin
  25. Lamotrigine
  26. Carbamazepine
  27. Ramelteon

Summary

Phenytoin is an anticonvulsant drug used to treat seizures. Phenytoin has a narrow therapeutic range of 10-20 mcg/mL. High doses of phenytoin above this cutoff can lead to symptoms of acute toxicity.  These symptoms include ataxia, slurred speech, and nystagmus. The provider should be notified immediately if these symptoms are seen. Another expected side effect of phenytoin is gingival hyperplasia, so encourage your patients to practice good oral hygiene and visit the dentist regularly.

Key Points

  • Phenytoin (Dilantin)
    • Mechanism
      • Anticonvulsants/antiseizure
        • Inhibits sodium influx and reduces repetitive neuron firing to limit seizures
    • Clinical Use
      • Seizures
        • Effective in treating tonic-clonic and partial seizures, but not absence seizures
      • Arrhythmias
        • Has been shown to be effective in treating ventricular tachycardia
    • Side Effects and Adverse Reactions
      • Acute toxicity/overdose
        • Narrow therapeutic range of 10-20 mcg/mL
          • Below this range, seizures may not be controlled. Above this range is considered phenytoin toxicity
        • Ataxia, nystagmus, slurred speech, decreased LOC
        • If these symptoms are noticed, the dose should be held and the provider contacted
      • Gingival hyperplasia
        • An expected side effect that can often be limited with good oral hygiene and regular dentist appointments
        • This is NOT a reason to stop the drug
      • Drug-drug interactions
        • Be careful when taking concurrently with anticoagulants, antipsychotics, sulfonamides, barbiturates, sucralfate, rifampin, antacids, warfarin, and antineoplastic medications
        • Note that drug interactions may be the reason for drug overdose/toxicity
      • Injection site reactions
        • Phenytoin is a vesicant, meaning that if it leaks from the vein into the surrounding tissue it can cause a burning sensation and tissue/skin damage
      • Blood Dyscrasias
        • Thrombocytopenia (low platelets)
        • Leukopenia (low white blood cells)
        • Monitor CBC levels