## **Core Concept**
The question tests knowledge on the treatment of pharyngitis caused by Group A beta-hemolytic streptococcus (GABHS), a common cause of bacterial sore throat. The management involves antibiotics to prevent complications and reduce symptom duration. **Penicillin** and **Amoxicillin** are commonly recommended for GABHS infections.

## **Why the Correct Answer is Right**
The correct answer, **Penicillin**, is the drug of choice for treating GABHS pharyngitis. This is because GABHS remains susceptible to penicillin in most regions, and it effectively reduces the duration and severity of symptoms, as well as the risk of complications like rheumatic fever and peritonsillar abscess. **Penicillin V** is often prescribed for its oral bioavailability.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although not specified, common alternatives like **Erythromycin** or **Azithromycin** (macrolides) are used in patients allergic to penicillin, not as the first line.
- **Option B:** This option is incorrect as **Amoxicillin** is also effective but typically reserved for patients who cannot take penicillin or have specific indications like co-infection with *H. pylori* or in combination with a beta-lactamase inhibitor for broader coverage.
- **Option D:** This option is incorrect as **Cefalexin** (a cephalosporin) might be used in some cases of skin infections or where GABHS is suspected but not confirmed, but it's not the first choice for GABHS pharyngitis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that a **10-day course** of antibiotics is recommended for GABHS pharyngitis to ensure eradication of the bacteria and prevent rheumatic fever. This duration is crucial for preventing complications.

## **Correct Answer:** . Penicillin