What antibiotic can be given to a patient with a penicillin (PCN) allergy for strep throat?

Treatment of Strep Throat in Penicillin-Allergic Patients

For patients with non-immediate (non-anaphylactic) penicillin allergy, prescribe a first-generation cephalosporin such as cephalexin 500 mg orally twice daily for 10 days; for patients with immediate/anaphylactic penicillin allergy, prescribe clindamycin 300 mg orally three times daily for 10 days. 1

Treatment Algorithm Based on Allergy Type

Step 1: Determine the Type of Penicillin Allergy

The critical first step is distinguishing between immediate and non-immediate reactions:

• Immediate/anaphylactic reactions include anaphylaxis, angioedema, respiratory distress, hives, or urticaria occurring within 1 hour of penicillin administration 1
• Non-immediate reactions include delayed rashes, mild gastrointestinal symptoms, or other non-life-threatening reactions occurring after 1 hour 1

This distinction is crucial because up to 10% of patients with immediate hypersensitivity to penicillin have cross-reactivity with first-generation cephalosporins, making all beta-lactams unsafe in this group 1, 2

Step 2: Select the Appropriate Antibiotic

For Non-Immediate Penicillin Allergy (Preferred Option)

• First-generation cephalosporins are the preferred first-line alternatives with strong, high-quality evidence supporting their efficacy 1, 2
• Cephalexin 500 mg orally twice daily for 10 days (adults) or 20 mg/kg per dose twice daily for 10 days (children, maximum 500 mg/dose) 1, 3
• Cefadroxil 1 gram once daily for 10 days (adults) or 30 mg/kg once daily for 10 days (children, maximum 1 gram) is an alternative once-daily option 1
• The cross-reactivity risk with first-generation cephalosporins is only 0.1% in patients with non-severe, delayed penicillin reactions 1

For Immediate/Anaphylactic Penicillin Allergy

Clindamycin is the preferred choice for patients who must avoid all beta-lactams:

• Clindamycin 300 mg orally three times daily for 10 days (adults) or 7 mg/kg per dose three times daily for 10 days (children, maximum 300 mg/dose) 1, 4
• Clindamycin has strong, moderate-quality evidence and demonstrates high efficacy in eradicating streptococci, even in chronic carriers 1
• Clindamycin resistance is only approximately 1% among Group A Streptococcus in the United States, making it highly reliable 1
• The FDA label confirms clindamycin is indicated for serious infections due to susceptible streptococci and should be reserved for penicillin-allergic patients 4

Macrolides are acceptable alternatives but less preferred:

• Azithromycin 500 mg once daily for 5 days (adults) or 12 mg/kg once daily for 5 days (children, maximum 500 mg) 1, 3
• Clarithromycin 250 mg twice daily for 10 days (adults) or 7.5 mg/kg per dose twice daily for 10 days (children, maximum 250 mg/dose) 1
• Erythromycin 250-500 mg every 6 hours for 10 days (adults) or 20-40 mg/kg/day divided 2-3 times daily for 10 days (children, maximum 1 gram/day) 1, 5
• The FDA label confirms erythromycin is indicated for streptococcal infections in penicillin-allergic patients 5

Critical Treatment Duration Requirements

• All antibiotics except azithromycin require a full 10-day course to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 1, 2, 3
• Azithromycin is the only exception, requiring only 5 days due to its prolonged tissue half-life 1, 3
• Shortening the course by even a few days results in appreciable increases in treatment failure rates and rheumatic fever risk 1

Important Resistance Considerations

• Macrolide resistance among Group A Streptococcus is approximately 5-8% in the United States and varies geographically, with some areas experiencing much higher rates 1
• Clindamycin resistance remains very low at approximately 1%, making it more reliable than macrolides when beta-lactams cannot be used 1
• Be aware of local macrolide resistance patterns before prescribing azithromycin, clarithromycin, or erythromycin 1, 2

Common Pitfalls to Avoid

• Do not use cephalosporins in patients with immediate/anaphylactic penicillin reactions due to the 10% cross-reactivity risk 1, 2
• Do not assume all penicillin-allergic patients cannot receive cephalosporins - only those with immediate/anaphylactic reactions should avoid them 1
• Do not prescribe shorter courses than recommended (except azithromycin's 5-day regimen), as this increases treatment failure and rheumatic fever risk 1
• Do not use azithromycin or other macrolides as first-line when cephalosporins can be safely used in non-immediate allergy 1, 3
• Do not prescribe broad-spectrum cephalosporins (cefaclor, cefuroxime, cefixime, cefdinir, cefpodoxime) when narrow-spectrum first-generation agents are appropriate, as they are more expensive and more likely to select for antibiotic-resistant flora 1

Why Clindamycin Over Macrolides for Immediate Allergy

While both are acceptable, clindamycin is preferred over macrolides for several reasons:

• Lower resistance rate (1% vs. 5-8% for macrolides) 1
• Higher efficacy in chronic carriers and treatment failures 1
• More reliable bacterial eradication compared to macrolides 1
• Macrolides have higher rates of gastrointestinal side effects, particularly erythromycin 6, 7

Special Considerations

• For patients with recurrent streptococcal pharyngitis, clindamycin may be particularly effective due to its ability to eradicate the organism in chronic carriers 1
• Chronic carriers generally do not require treatment, as they are unlikely to spread infection or develop complications 1
• Acetaminophen or NSAIDs can be used for moderate to severe symptoms or high fever, while aspirin should be avoided in children due to risk of Reye syndrome 1
• Corticosteroids are not recommended as adjunctive therapy 1