Which of the following is a sign of carbamazepine toxicity?

• A. Generalized seizures
• B. Rash
• C. Dizziness
• D. Arrhythmia

Answer: (D)

Carbamazepine toxicity can disrupt the heart’s electrical activity because the drug blocks voltage-gated sodium channels in cardiac tissue, just as it does in the brain. When levels are toxic, this interference slows conduction and can lead to abnormal heart rhythms, i.e., arrhythmias. This makes arrhythmia a key sign of significant toxicity. Dizziness is a common side effect and can occur at therapeutic or mild toxic levels, so it isn’t as specifically indicative of dangerous toxicity. Rash can occur as a hypersensitivity reaction but isn’t a direct marker of toxic levels. Generalized seizures reflect CNS effects but don’t specifically point to cardiac toxicity, so arrhythmias are the most telling sign in this context.