## **Core Concept**
The question pertains to the use of levonorgestrel as emergency contraception to prevent pregnancy after unprotected intercourse. Levonorgestrel is a synthetic progestogen that can be used to prevent ovulation or implantation of a fertilized egg when taken as emergency contraception.

## **Why the Correct Answer is Right**
The standard regimen for levonorgestrel emergency contraception when used in a two-dose regimen is 0.75 mg taken twice, with the second dose taken 12 hours after the first dose. This specific dosing regimen is designed to maximize the efficacy of levonorgestrel in preventing pregnancy. The mechanism involves inhibiting or delaying ovulation, thereby preventing fertilization, or possibly interfering with implantation if fertilization has occurred.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests taking the next tablet immediately, which does not align with the recommended 12-hour interval between doses.
- **Option B:** This option suggests a 24-hour interval, which is longer than the recommended interval for the two-dose regimen of levonorgestrel.
- **Option D:** This option suggests a 6-hour interval, which is shorter than the recommended interval.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the effectiveness of levonorgestrel as emergency contraception is highly dependent on the timing of administration, with efficacy decreasing over time after unprotected intercourse. The sooner it is taken after intercourse, the better its effectiveness. For maximum efficacy, the first dose of 0.75 mg of levonorgestrel should be taken as soon as possible after unprotected intercourse, and the second dose 12 hours later.

## **Correct Answer:** B. 12 hours later.