# A young woman on stable carbamazepine therapy for epilepsy reports a new unplanned pregnancy. Which counseling regarding her contraceptive history is most accurate?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=391744&lang=en  
> language: en  
> subject: Medical Emergencies  
> category: PA

## Question

A young woman on stable carbamazepine therapy for epilepsy reports a new unplanned pregnancy. Which counseling regarding her contraceptive history is most accurate?

## Option

1. "Pregnancy is a known cure for epilepsy; you can stop carbamazepine now."
2. "Carbamazepine induces CYP3A4, accelerating COC metabolism; non-hormonal or higher-dose contraception is needed during therapy." **✔ Correct answer**
3. "Combined OC effectiveness is unaffected by anticonvulsants."
4. "The COC failed because you missed doses; nothing else could have prevented this."

**Correct answer: 2**

## Explanation

Correct (2): Carbamazepine is a potent CYP3A4 inducer and autoinducer — it accelerates metabolism of estrogen-containing contraceptives, reducing efficacy. Women on enzyme-inducing anticonvulsants need higher-estrogen COCs, copper IUD, depot medroxyprogesterone, or barrier methods. (1) Blames the patient incorrectly. (3) Pregnancy does not cure epilepsy. (4) Effectiveness is significantly reduced.

## In-depth explanation

Memory Tip Enzyme-inducing anticonvulsants (phenytoin, carbamazepine, phenobarbital, topiramate >200 mg) reduce hormonal contraceptive effectiveness. Safe: copper IUD, depot MPA, levonorgestrel IUD.

## Clinical scenario

Scenario 24-year-old female on carbamazepine 200 mg PO BID × 18 months for partial seizures. Concurrent combined oral contraceptive (COC). Now 8 weeks pregnant despite COC adherence.

## Key concepts

- **CYP3A4 induction** — Increased activity of CYP3A4 enzyme accelerating metabolism of co-administered drugs; carbamazepine is a strong inducer.
- **Autoinduction** — Carbamazepine's induction of its own metabolism over 2-4 weeks; levels may drop and require dose increase.
- **Drug-contraceptive interaction** — Reduced effectiveness of hormonal contraceptives when enzyme-inducing drugs are co-administered.

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