Final answer:
For patients with pharyngitis/tonsillitis who are allergic to penicillin, first-line treatments include macrolides such as erythromycin or azithromycin, and sometimes cephalosporins, although cross-reactivity must be considered in severe penicillin allergies.
Step-by-step explanation:
The first-line treatment for pharyngitis/tonsillitis in a patient with a penicillin allergy generally includes alternative antibiotics such as macrolides or cephalosporins. Given that penicillin and its derivatives, like amoxicillin, are the common treatment for bacterial infections but are not an option for patients with allergies, alternatives must be used. For example, macrolides like erythromycin or azithromycin can be prescribed.
Moreover, if the allergy is not severe, a cephalosporin may be considered since it is structurally different from penicillins and might be tolerated by some patients with penicillin allergies. However, care must be taken, especially with cephalosporins, due to potential cross-reactivity in patients with a history of severe penicillin allergy.