**Core Concept**
WHO recommends a standardized treatment regimen for leprosy, classified into two categories: paucibacillary and multibacillary, based on the bacterial load and severity of the disease. Multibacillary leprosy is characterized by a high bacterial load and a more severe clinical presentation.

**Why the Correct Answer is Right**
Multibacillary leprosy requires a longer duration of treatment to effectively eliminate the bacteria and prevent relapse. The WHO-recommended treatment regimen for multibacillary leprosy involves a combination of rifampicin, clofazimine, and dapsone for 12 months. This prolonged treatment duration helps to reduce the bacterial load and minimize the risk of resistance development.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the treatment duration for paucibacillary leprosy is typically shorter, usually 6 months.
* **Option B:** This option is incorrect because the treatment regimen for multibacillary leprosy does not involve a single antibiotic, but rather a combination of rifampicin, clofazimine, and dapsone.
* **Option C:** This option is incorrect because the treatment duration for multibacillary leprosy is longer than 6 months, typically 12 months.

**Clinical Pearl / High-Yield Fact**
It is essential to accurately diagnose and classify leprosy to determine the appropriate treatment duration and regimen. A delay in treatment can lead to progression of the disease and increased risk of complications.

**Correct Answer:** C. 12 months