MCQ: Carbamazepine

Q1) Which of the following statements is true about carbamazepine:-

A) It is indicated in complex partial seizures.

B) It is an enzyme inhibitors

C) It can cause megaloblastic anaemia

D) It is the drug of choice for status epilepticus.

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So, the answer to the above question is an option 

A) It is indicated in complex partial seizures.

Let's get started with Carbamazepine:-

It is an antiepileptic drug that acts by lengthening the inactivated state of the Na+ channel. 

Uses:-

1) DOC for Partial seizure/trigeminal neuralgia.

2) Bipolar disorder.

3) Acute mania

4) GTCS.

Let's rule out other options:-

Option B) It's an enzyme inducer. It is a substrate as well as inducer for CYP3A4 and CYP2C9. Oxcarbazepine is a less powerful CYP enzyme inducer.

Option C) Carbamazepine causes agranulocytosis or aplastic anaemia and not megaloblastic anaemia.

Other side effects include:

1) Hyponatremia: Delayed and more common in the elderly. Risk is higher in Oxcarbazepine.

2) Hypersensitivity

4) Hepatoxicity 

3) Steven Johnson syndrome (Associated with HLA-B 1502 gene)

4) Ataxia 

4) Blurred vision/ Diplopia 

For the last two side effects, we need TDM for adjusting the dose. Remember, Ataxia and Blurred vision is not a Idiosyncratic reactions.

Let's do questions related to Carbamazepine!

Q1) What adverse effect is risked to ongoing valproate therapy?

-Hepatotoxicity.

Q2) A cancer patient is on anticancer drugs (vincristine etc) and develops multiple episodes of seizures, refractory to diazepam and lidocaine. Blood tests show elevated ADH and euvolemic hyponatremia. Which drug can be used to treat this patient?

- You can't use Carbamazepine because it causes increase sensitivity of renal tubules to ADH levels. 

In this case, we use Phenytoin which causes a decrease in ADH secretion and corrects hyponatremia.

~Ojas