From the Guidelines
For strep A pharyngitis that is resistant to ampicillin but the patient is currently on amoxicillin, I recommend switching to an alternative antibiotic, such as penicillin G benzathine as a single intramuscular injection of 1.2 million units, as it is a strong and high-quality recommendation for individuals without penicillin allergy 1. The best options for treatment include:
- Penicillin G benzathine as a single intramuscular injection of 1.2 million units
- Oral cephalosporins such as cefdinir, cefpodoxime, or cefuroxime, however, the provided evidence does not specify the exact dosing for these medications for this specific condition, but they are recommended for individuals without penicillin allergy
- For patients with penicillin allergy, macrolides like azithromycin or clindamycin are appropriate alternatives, with dosing as follows:
- Azithromycin: 12 mg/kg once daily (max = 500 mg) for 5 days 1
- Clindamycin: 7 mg/kg/dose 3 times daily (max = 300 mg/dose) for 10 days 1 This change is necessary because resistance to ampicillin indicates potential resistance to amoxicillin as well, since both are beta-lactam antibiotics with similar mechanisms of action and resistance patterns. Group A Streptococcus develops resistance through altered penicillin-binding proteins or beta-lactamase production, which affects both medications equally. Complete the full course of the new antibiotic to ensure eradication of the infection and prevent complications like rheumatic fever or post-streptococcal glomerulonephritis. It is essential to note that the provided evidence does not explicitly address the resistance of strep A pharyngitis to ampicillin, but it does provide recommendations for the treatment of strep A pharyngitis in general, which can be applied to this scenario. The most recent and highest quality study 1 provides strong and high-quality recommendations for the treatment of strep A pharyngitis, which should be prioritized in this scenario.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Treatment of Strep A Pharyngitis
If a patient is on amoxicillin but resistant to ampicillin, the following options can be considered:
- Cephalosporins: There is low-certainty evidence that cephalosporins may be more effective than penicillin for symptom resolution and clinical relapse in adults 2, 3, 4.
- Macrolides: There is no difference in symptom resolution between macrolides and penicillin 2, 3, 4.
- Carbacephem: There is low-certainty evidence that carbacephem may be more effective than penicillin for symptom resolution in adults and children 2, 3, 4.
- Clindamycin: One trial compared clindamycin with ampicillin, but the results are not conclusive 2.
- Azithromycin: One unpublished trial in children found a better cure rate for azithromycin in a single dose compared to amoxicillin for 10 days, but there was no difference between the groups in ITT analysis or at long-term follow-up 3, 4.
Considerations
- The choice of antibiotic should be based on the patient's age, allergy history, and local resistance patterns.
- Penicillin can still be regarded as a first choice treatment for both adults and children, considering its low cost and absence of resistance 2, 3, 4.
- The use of antibiotics should be guided by clinical guidelines and diagnostic methods to minimize unnecessary use and prevent complications 5.