Is cefdinir (Cephalosporin) safe to prescribe to someone with an allergy to amoxicillin (Penicillin)?

Cefdinir Safety in Patients with Amoxicillin Allergy

Cefdinir can be safely prescribed to most patients with an amoxicillin allergy, but the safety depends on the type and timing of the previous allergic reaction to amoxicillin. 1, 2

Risk Assessment Based on Reaction Type

Immediate-Type Reactions (IgE-mediated)

• Patients with immediate-type allergic reactions to amoxicillin can safely receive cefdinir as it has dissimilar side chains to amoxicillin 1
• Cross-reactivity between penicillins and cephalosporins with dissimilar side chains is minimal, with overall cross-reactivity rates around 1% 3
• If the immediate-type reaction to amoxicillin occurred >5 years ago, the risk is even lower as IgE-mediated penicillin allergy wanes over time 4

Delayed-Type Reactions

• Patients with non-severe, delayed-type allergic reactions to amoxicillin can safely receive cephalosporins with dissimilar side chains like cefdinir, regardless of when the reaction occurred 1
• If the delayed-type reaction occurred >1 year ago, the risk of cross-reactivity is further reduced 1

Side Chain Considerations

• Cross-reactivity between penicillins and cephalosporins is primarily determined by similarity in R1 side chains 5, 3
• Cefdinir has dissimilar side chains to amoxicillin, making it a safer choice compared to cephalosporins with similar side chains (like cephalexin, cefaclor, or cefamandole) 1, 5
• Third-generation cephalosporins like cefdinir carry a negligible risk of cross-allergy in penicillin-allergic patients 3

FDA Labeling and Precautions

• The FDA label for cefdinir advises caution when prescribing to penicillin-sensitive patients, noting that cross-hypersensitivity among β-lactam antibiotics may occur in up to 10% of patients with penicillin allergy 2
• However, this 10% figure is now considered outdated, with more recent studies showing much lower rates of cross-reactivity, especially for cephalosporins with dissimilar side chains 6, 4
• Before prescribing cefdinir, a careful inquiry about previous hypersensitivity reactions to cephalosporins, penicillins, or other drugs should be made 2

Monitoring and Management

• If cefdinir is prescribed to a patient with amoxicillin allergy, monitor for potential allergic reactions, especially during the first dose 2
• If an allergic reaction occurs, discontinue cefdinir immediately 2
• Serious acute hypersensitivity reactions may require emergency treatment with epinephrine, oxygen, IV fluids, antihistamines, corticosteroids, and airway management 2

Common Pitfalls and Caveats

• Avoiding appropriate cephalosporin therapy due to reported penicillin allergy can lead to use of broader-spectrum antibiotics, increasing risks of antimicrobial resistance and C. difficile infection 4
• Many reported penicillin allergies are not true allergies - fewer than 5% of patients with reported penicillin allergy have clinically significant hypersensitivity 4
• The historical warning against using cephalosporins in penicillin-allergic patients has been largely refuted by modern evidence 6
• The risk of avoiding appropriate cephalosporin therapy often outweighs the minimal risk of cross-reactivity 6, 4

In conclusion, cefdinir can be safely prescribed to patients with amoxicillin allergy in most cases, particularly when the allergic reaction was non-severe or occurred more than a year ago. The risk of cross-reactivity is minimal due to the dissimilar side chains between cefdinir and amoxicillin.