Carbamazepine
A sodium channel-blocking antiepileptic for focal and tonic-clonic seizures, trigeminal neuralgia and bipolar disorder.
Drug card
- How it works
- Blocking neuronal sodium channels to stop rapid, repetitive firing
- Used for
- Focal and generalized tonic-clonic seizures
- Trigeminal neuralgia
- Bipolar disorder when lithium has not worked
- Known for
- SJS and TEN, mainly in HLA-B*15:02 carriers
- Agranulocytosis
- Low sodium (hyponatremia)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does carbamazepine work?
Carbamazepine, a tricyclic compound related to the tricyclic antidepressants, blocks sodium channels in a use- and voltage-dependent way and stops repetitive firing. CYP3A4 turns it into an active 10,11-epoxide. It induces its own metabolism (autoinduction), so its half-life shortens over the first weeks.
Like other sodium channel-blocking antiepileptics: These drugs block voltage-gated sodium channels in neurons in a use- and voltage-dependent way: the faster a neuron fires, the more channels they block. Ordinary signaling carries on, but the sustained high-frequency bursts that spread a seizure are cut short. Phenytoin and carbamazepine are also strong inducers of liver enzymes, so they speed the breakdown of many other drugs.
Uses
What is carbamazepine used for?
- Focal and generalized tonic-clonic seizures
- Trigeminal neuralgia
- Bipolar disorder when lithium has not worked
Side effects
Side effects of carbamazepine
- SJS and TEN, mainly in HLA-B*15:02 carriersKnown forSerious
- AgranulocytosisKnown forSerious
- Low sodium (hyponatremia)Known forSerious
- Dizziness
- Drowsiness and tiredness
- Unsteadiness and poor coordination (ataxia)
- Double vision
- Nausea and vomiting
- Aplastic anemiaSerious
- Liver injurySerious
- Birth defects such as spina bifidaSerious
- Heart blockSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Test for HLA-B*15:02 before starting in people of South or Southeast Asian ancestry: carriers have a much higher risk of SJS/TEN.
- Get a full blood count before starting; stop it if significant bone marrow depression develops.
- As an enzyme inducer it can make hormonal contraceptives fail and lowers levels of DOACs and many other drugs.
- It does not control absence or myoclonic seizures and can worsen atypical absences; avoid with MAOIs.
Good to know: HLA-B*15:02 is carried by over 15% of people in Thailand, Malaysia and Hong Kong and by about 2 to 4% of South Asians, including Indians.
Remember it
A way to remember it
Sodium channel blockers let single shots through but jam the machine gun.
Their block grows with each firing, so ordinary signals pass while the rapid, repetitive bursts of a seizure are stopped.
Written for biofideX
Its class
Sodium channel-blocking antiepileptics
Other sodium channel-blocking antiepileptics with a card:
Easily mixed up with local anesthetics, valproate and succinimides.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Carbamazepine tablets: label (DailyMed)
- Carbamazepine 200 mg prolonged-release tablets: SmPC (emc)
- Carbamazepine (NCI Thesaurus)
- Carbamazepine (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Epilepsy and nerve pain
Carbamazepine is one of 8 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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