Carbamazepine

Summary

Carbamazepine is a drug that works by blocking sodium channels in neurons to reduce excessive neuronal firing. Over time, it may cause autoinduction, meaning it stimulates its own metabolism in the liver.
Clinically, carbamazepine is used as an antiepileptic to treat various types of seizures. It is also used as a mood stabilizer to treat bipolar disorder. Carbamazepine can also be used to treat neuropathic pain and trigeminal neuralgia.

The therapeutic range for carbamazepine is between 4 to 12 mcg/mL.

Potential side effects of carbamazepine include Stevens-Johnson syndrome, rash, drowsiness, dizziness, ataxia, aplastic anemia, thrombocytopenia, and agranulocytosis.

Carbamazepine has lots of drug interactions because it induces liver enzymes. Notably, it can decrease the effectiveness of oral contraceptives. Patients taking carbamazepine should also avoid grapefruit juice

Key Points

• Carbamazepine
  • Mechanism
    • Sodium channel blocker
      • Carbamazepine inactivates sodium channels, which slows the entrance of sodium into the neuron, thus slowing down the rate at which the neuron can fire
    • Metabolized by the liver
      • May cause autoinduction
        • A process where a drug stimulates the production of enzymes in the liver that enhance its own metabolism.
        • Typically results in a decrease in the plasma concentration of the drug over time, which can reduce the drug's efficacy unless the dosage is adjusted.
        • To maintain therapeutic effectiveness, it may be necessary to increase the dose of carbamazepine over time.
  • Therapeutic Level
    • 4-12 mcg/mL
      • Below this level, the drug level isn’t high enough to be effective
      • Above this level, the patient is at higher risk for toxicity symptoms
  • Clinical Use
    • Seizures
      • Often called an antiepileptic or anticonvulsant
      • Effective in treating partial seizures and tonic-clonic seizures
      • NOT effective in treating absence, myoclonic, or akinetic seizures and has even been shown to potentially increase the frequency of these seizure types
    • Mood stabilizer
      • Bipolar disorder
        • Used to acutely treat manic episodes
        • Used off-label as a maintenance therapy
    • Neuropathic pain
      • Trigeminal neuralgia
        • A chronic pain condition affecting the trigeminal nerve, characterized by severe pain along the lower face and jaw
        • Carbamazepine has been proven to be effective in treating the pain associated with trigeminal neuralgia
  • Side Effects
    • Blood dyscrasias
      • Thrombocytopenia
        • Low platelets
        • Monitor for signs of bruising and/or bleeding
      • Aplastic Anemia
        • Low red blood cells
      • Agranulocytosis
        • Low white blood cells
        • May include leukopenia and neutropenia
        • Monitor for signs of infection (sore throat, fever, fatigue, etc.)
      • Monitor CBC
      • Carbemazepine is contraindicated with bleeding disorders and bone marrow suppression
    • CNS effects
      • Ataxia
        • Loss of coordination
      • Dizziness
      • Drowsiness
    • Stevens-Johnson Syndrome (SJS)
      • A medical emergency
      • A hypersensitivity skin reaction characterized by severe blisters and rashes on the skin and mucous membranes, flu-like symptoms, and eye problems
  • Interactions
    • Lots of drug interactions
      • Carbamazepine is a CYP enzyme inducer, meaning it accelerates the metabolism activity of enzymes in the liver. Any other medications that are also metabolized in the liver will have an accelerated breakdown and reduced effectiveness, including
        • Warfarin
        • Steroids
        • Theophylline
    • Decreases effectiveness of oral contraceptives
      • Consider other forms of birth control to prevent pregnancy
    • Avoid grapefruit juice
      • Grapefruit juice interferes with how carbamazepine is metabolized in the body
      • A buildup of carbamazepine in the blood can lead to toxicity