Is Streptococcus pyogenes susceptible to amoxicillin (Amoxil)?

From the Guidelines

Streptococcus pyogenes remains universally susceptible to penicillins, and amoxicillin is an effective treatment option for infections caused by this bacterium. According to the guideline for the management of acute sore throat 1, penicillin has been the treatment of choice for group A b-haemolytic streptococcal pharyngitis for five decades, and amoxicillin is often used in younger children due to its taste and availability. The guideline states that group A b-haemolytic streptococci have not developed resistance to any of the penicillins or shown an increase in penicillin minimal inhibitory concentrations over at least five decades.

Key Points to Consider

• Amoxicillin is considered an effective first-line treatment for strep throat and other infections caused by Streptococcus pyogenes.
• The typical adult dosage is 500 mg orally three times daily or 875 mg twice daily for 10 days.
• For children, the dosage is typically 45-90 mg/kg/day divided into two or three doses.
• It's essential to complete the full course of antibiotics even if symptoms improve before completion to ensure complete eradication of the bacteria and prevent complications.
• Amoxicillin works by inhibiting bacterial cell wall synthesis, which is effective against S. pyogenes because this organism remains universally susceptible to penicillins.

Alternative Treatment Options

• For patients with penicillin allergy, alternatives include cephalexin, azithromycin, or clindamycin.
• Taking amoxicillin with food can help reduce gastrointestinal side effects, though it can be taken without food as well.
• The practice guidelines for the diagnosis and management of skin and soft-tissue infections 1 also support the use of penicillin and amoxicillin as effective treatment options for infections caused by Streptococcus pyogenes.

From the FDA Drug Label

Amoxicillin for oral suspension is indicated in the treatment of infections due to susceptible (ONLY β-lactamase–negative) isolates of Streptococcusspecies. (α-and β-hemolytic isolates only), It is recommended that there be at least 10 days’ treatment for any infection caused by Streptococcus pyogenesto prevent the occurrence of acute rheumatic fever.

Strep pyogenes is a type of Streptococcus species. The drug label indicates that amoxicillin is effective against β-lactamase–negative isolates of Streptococcus species, which includes Streptococcus pyogenes.

• The recommended treatment duration for Streptococcus pyogenes infections is at least 10 days to prevent acute rheumatic fever 2.
• Amoxicillin can be used to treat infections caused by Streptococcus pyogenes, but only if the isolate is β-lactamase–negative.

From the Research

Strep Pyogenes Response to Amoxicillin

• Strep pyogenes, also known as Group A beta-hemolytic streptococcal pharyngitis, is a common infection that can be treated with antibiotics 3.
• Amoxicillin is considered a first-line antibiotic for the treatment of strep pyogenes, along with penicillin 3, 4.
• The recommended course of amoxicillin for strep pyogenes is 10 days 3, 4.
• Studies have shown that amoxicillin is effective in eradicating strep pyogenes from the throat and preventing complications such as rheumatic fever 5, 4.
• However, there is some evidence to suggest that amoxicillin may not be as effective as other antibiotics, such as cephalosporins, in certain cases 6.
• A study comparing azithromycin to amoxicillin in children found that azithromycin was associated with lower bacteriologic eradication rates, but similar clinical efficacy 7.

Comparison to Other Antibiotics

• Penicillin is also a commonly used antibiotic for the treatment of strep pyogenes, and is considered equally effective to amoxicillin 3, 4.
• Cephalosporins are another option for patients with penicillin allergy, and may be more effective than penicillin in certain cases 6.
• Macrolides, such as azithromycin, are also used to treat strep pyogenes, but may have lower eradication rates compared to penicillin and amoxicillin 6, 7.
• Carbacephem may be more effective than penicillin for symptom resolution in adults and children, but more research is needed to confirm this 6.