What is the efficacy of intramuscular (IM) penicillin for the treatment of streptococcal pharyngitis (strep throat)?

From the Guidelines

Intramuscular (IM) penicillin G benzathine is a recommended treatment option for strep throat (Group A Streptococcal pharyngitis) when oral therapy is not feasible or compliance is a concern, with a recommended dose of 1.2 million units for adults and 600,000 units for children weighing less than 27 kg, as supported by the Infectious Diseases Society of America guidelines 1.

Key Points

• The dose of IM penicillin G benzathine is weight-based, with 600,000 units for children weighing less than 27 kg and 1.2 million units for adults and children weighing 27 kg or more.
• This one-time injection provides adequate antibiotic levels for 3-4 weeks, which is sufficient to eradicate the infection.
• Common side effects include pain at the injection site, allergic reactions, and gastrointestinal disturbances.
• Before administration, patients should be screened for penicillin allergy.
• IM penicillin is particularly useful for patients who cannot swallow pills, have poor medication adherence, or need guaranteed treatment completion.

Mechanism of Action

• IM penicillin works by interfering with bacterial cell wall synthesis, causing bacterial cell death.

Clinical Considerations

• While oral antibiotics like penicillin V or amoxicillin are typically first-line treatments for strep throat, this injectable option ensures complete treatment and helps prevent complications such as rheumatic fever or post-streptococcal glomerulonephritis.
• The Infectious Diseases Society of America guidelines recommend IM penicillin G benzathine as a treatment option for strep throat, with a strong, high recommendation strength and quality 1.

Supporting Evidence

• The guidelines are based on a review of the literature, including studies on the efficacy and safety of IM penicillin G benzathine for the treatment of strep throat 1.
• The guidelines also consider the importance of preventing complications such as rheumatic fever and post-streptococcal glomerulonephritis, and the role of IM penicillin G benzathine in achieving this goal 1.

From the Research

Efficacy of Intramuscular Penicillin for Strep Throat

• The efficacy of intramuscular (IM) penicillin for the treatment of streptococcal pharyngitis has been studied in several clinical trials 2, 3, 4, 5, 6.
• A study published in JAMA in 1976 found that a single injection of 900,000 units of penicillin G benzathine and 300,000 units of penicillin G procaine was effective in treating streptococcal pharyngitis in children, with a high cure rate and minimal side effects 2.
• Another study published in The Pediatric infectious disease journal in 2000 noted that intramuscular benzathine penicillin is an inexpensive and effective treatment option for streptococcal pharyngitis, especially in cases where compliance is a concern 3.
• A randomized controlled trial published in Clinical pediatrics in 2011 compared the efficacy of oral amoxicillin with intramuscular benzathine penicillin G in treating streptococcal pharyngitis in children, and found that both treatments were effective, but that compliance was a major issue with oral amoxicillin 4.
• A study published in Annals of emergency medicine in 1995 discussed the cost-effective diagnosis and treatment of group A streptococcal tonsillopharyngitis, and noted that a single IM injection of benzathine penicillin is effective and obviates compliance issues 5.
• However, a study published in Pediatrics in 2001 found that the microbiological efficacy of intramuscular benzathine penicillin G and oral penicillin V in eradicating group A streptococci from children with acute pharyngitis was lower than expected, with a significant number of treatment failures 6.

Treatment Outcomes

• The studies suggest that intramuscular penicillin can be an effective treatment option for streptococcal pharyngitis, especially in cases where compliance is a concern 2, 3, 4, 5.
• However, the efficacy of intramuscular penicillin may be lower than expected in some cases, with a significant number of treatment failures 6.
• The choice of treatment should be based on individual patient needs and circumstances, taking into account factors such as compliance, cost, and potential side effects 3, 4, 5.