Neural tube defects are associated with which drugs?
**Core Concept**
Neural tube defects (NTDs) are congenital anomalies of the brain and spine that occur during embryonic development. They are associated with genetic and environmental factors, including exposure to certain medications during early pregnancy.
**Why the Correct Answer is Right**
Folic acid supplementation is widely recommended to pregnant women to prevent NTDs. However, some medications can interfere with folate metabolism or increase the risk of NTDs. Valproate, a medication used to treat epilepsy and bipolar disorder, is a known teratogen that increases the risk of NTDs. It inhibits dihydrofolate reductase (DHFR), an enzyme involved in folate metabolism, leading to a decrease in folate levels and an increased risk of NTDs.
**Why Each Wrong Option is Incorrect**
**Option A:** Isotretinoin (Accutane) is a retinoid used to treat acne. While it is a teratogen, it is not specifically associated with an increased risk of NTDs.
**Option B:** Phenytoin is an antiepileptic medication, but it is not as strongly associated with NTDs as valproate. However, it can have other teratogenic effects.
**Option C:** Methotrexate is a chemotherapeutic agent and immunosuppressant that can cause fetal abnormalities, but its association with NTDs is not as strong as valproate.
**Clinical Pearl / High-Yield Fact**
Valproate is a category X medication, meaning it should not be used in pregnancy due to a high risk of fetal harm. Pregnant women taking valproate should be closely monitored, and alternative medications should be considered if possible.
**Correct Answer: C. Valproate**