Final answer:
For patients with a penicillin allergy, Azithromycin, a macrolide antibiotic, is an advisable alternative because it is not related to penicillins and is considered safe for such individuals.
Step-by-step explanation:
If there is a penicillin allergy, you should avoid any drug that is part of the penicillin class, as allergic reactions can be severe. Amoxicillin, which is option 1, is a type of penicillin derivative and therefore not suitable for someone with a penicillin allergy. Option 2, Cephalexin, is a beta-lactam antibiotic related to the penicillins and may not be suitable for people with a severe penicillin allergy due to possible cross-reactivity. However, option 3, Azithromycin, is a type of macrolide antibiotic which is usually considered safe for patients with penicillin allergies. It works by blocking protein synthesis in microorganisms, effectively destroying infectious agents without the risk associated with penicillin. Therefore, in the context of a penicillin allergy, Azithromycin would be the advisable choice.