## **Core Concept**
Methotrexate is a folate antagonist used in the medical management of ectopic pregnancy. It works by inhibiting dihydrofolate reductase, an enzyme critical for DNA synthesis and cell division, thereby terminating the rapidly dividing trophoblastic cells of the ectopic pregnancy. The effectiveness of methotrexate in treating ectopic pregnancy depends on proper dosing and administration.

## **Why the Correct Answer is Right**
The correct answer involves the intramuscular (IM) route of administration for methotrexate in the treatment of ectopic pregnancy. The standard dose is **50 mg/m²** body surface area, administered intramuscularly. This dosing regimen is critical for achieving therapeutic levels of methotrexate that can effectively terminate the ectopic pregnancy while minimizing side effects. The use of body surface area for dosing helps to standardize the treatment across patients of different sizes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Incorrect because it specifies an oral route, which is not the standard for methotrexate administration in ectopic pregnancy treatment due to concerns about bioavailability and gastrointestinal side effects.
- **Option B:** Incorrect as it suggests a different dose or route that is not standard for ectopic pregnancy treatment.
- **Option D:** Incorrect because it either suggests an incorrect dose or an inappropriate route of administration compared to the standard practice.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that methotrexate for ectopic pregnancy is given **intramuscularly** at a dose of **50 mg/m²**. Monitoring of beta-hCG levels is crucial after treatment to assess the success of the therapy. A significant decrease in beta-hCG levels indicates a successful treatment outcome.

## **Correct Answer:** . 50 mg/m² intramuscularly.