What is the role of Penicillin (PCN) in the treatment of streptococcal pharyngitis?

From the Guidelines

Penicillin remains the first-line treatment for strep pharyngitis (Group A Streptococcal pharyngitis). For adults, the recommended regimen is penicillin V potassium 500 mg orally twice daily for 10 days 1. Alternatively, amoxicillin 1000 mg once daily for 10 days or 500 mg twice daily for 10 days is equally effective and may offer better compliance due to its taste. For patients with penicillin allergy, alternatives include cephalexin 500 mg twice daily for 10 days (if non-anaphylactic allergy) or macrolides such as azithromycin 500 mg on day 1, then 250 mg daily for 4 more days (for severe penicillin allergy) 1. Some key points to consider when treating strep pharyngitis include:

• The full 10-day course of antibiotics should be completed even if symptoms resolve earlier to ensure bacterial eradication and prevent complications like rheumatic fever and post-streptococcal glomerulonephritis 1.
• Penicillin is preferred because it has a narrow spectrum of activity which reduces the risk of antimicrobial resistance, has proven efficacy in preventing rheumatic fever, and Group A Streptococcus has remained universally susceptible to penicillin with no documented resistance 1.
• The choice of antibiotic should be based on the patient's allergy history, the severity of the infection, and the potential for resistance 1.
• It is essential to differentiate between viral and bacterial pharyngitis to avoid unnecessary antibiotic use and reduce the risk of antimicrobial resistance 1.

From the Research

PCN for Strep Pharyngitis

• Penicillin (PCN) is the treatment of choice for streptococcal pharyngitis due to its cost, narrow spectrum of activity, and effectiveness 2.
• The recommended course of PCN is 10 days of oral therapy or one injection of intramuscular benzathine penicillin 2.
• Amoxicillin is equally effective and more palatable than PCN, and can be used as an alternative 2.
• Erythromycin and first-generation cephalosporins are options for patients with penicillin allergy 2, 3.

Effectiveness of PCN

• PCN has been shown to accelerate symptom relief, particularly fever and pain, by a day or two 4.
• However, there is no convincing evidence that PCN relieves symptoms in children 4.
• PCN has been shown to reduce the risk of acute rheumatic fever by about 75% 4.

Resistance and Adverse Effects

• There is significant resistance to azithromycin and clarithromycin in some parts of the United States 5.
• The adverse effects associated with PCN are mild, but there is a risk of rare but serious adverse effects, such as anaphylaxis 4.
• PCN can affect the bacterial ecology, encouraging resistance among some bacterial species other than group A streptococci 4.

Treatment Guidelines

• Guidelines recommend using clinical decision rules to assess the risk of group A beta-hemolytic streptococcal infection, followed by rapid antigen testing if a diagnosis is unclear, before prescribing antibiotics 5.
• Penicillin and amoxicillin are first-line antibiotics, with a recommended course of 10 days; first-generation cephalosporins are recommended for patients with nonanaphylactic allergies to penicillin 5.