**Core Concept**
The management of streptococcal pharyngitis involves the use of antibiotics to eliminate the causative bacteria, Streptococcus pyogenes, and prevent complications such as rheumatic fever. The chosen antibiotic should be effective against S. pyogenes and have a favorable safety profile.

**Why the Correct Answer is Right**
The antibiotic of choice for streptococcal pharyngitis is penicillin, specifically penicillin V or amoxicillin. These penicillins are effective against S. pyogenes due to their ability to inhibit cell wall synthesis by binding to penicillin-binding proteins (PBPs). This action results in the formation of a weakened bacterial cell wall, ultimately leading to bacterial lysis and death. Penicillin V and amoxicillin are also well-tolerated and have a long history of safe use in children and adults.

**Why Each Wrong Option is Incorrect**
**Option A:** Erythromycin is a macrolide antibiotic that may be used as an alternative in patients allergic to penicillin, but it is not the first-line treatment for streptococcal pharyngitis.
**Option B:** Cephalosporins, such as cephalexin, are effective against a broad range of bacteria, but they are not the preferred choice for streptococcal pharyngitis due to potential resistance and lower efficacy compared to penicillins.
**Option D:** Azithromycin is a macrolide antibiotic that is effective against S. pyogenes, but it is not the preferred choice for streptococcal pharyngitis due to concerns about resistance and potential side effects.

**Clinical Pearl / High-Yield Fact**
It is essential to complete the full 10-day course of antibiotic therapy to ensure eradication of S. pyogenes and prevent complications. Additionally, patients with streptococcal pharyngitis should be tested for carrier status to prevent transmission to others.

**Correct Answer: A. Penicillin V**