Which of the following medications is suggested if a patient is allergic to penicillin?

The suggested medication for a patient allergic to penicillin is cephalexin. Despite cephalexin belonging to the cephalosporin class, which is chemically related to penicillin, it is sometimes tolerated by patients with penicillin allergies. The cross-reactivity between penicillins and cephalosporins is believed to be lower than it once was thought to be, particularly with later generations of cephalosporins.

Cephalexin works by disrupting the synthesis of the bacterial cell wall, similar to penicillin, and is effective against a broad spectrum of bacteria. However, caution is still advised, and history of allergy must always be thoroughly assessed before prescribing it.

Other options are less suitable for patients with a penicillin allergy. Amoxicillin, being a derivative of penicillin, is not recommended for individuals with penicillin allergies. Carbapenems, while sometimes considered as alternatives, can also present a risk of cross-reactivity for certain patients. Metronidazole, though effective for anaerobic infections, does not serve as a substitute for penicillin-related infections as it operates through a different mechanism and is specific for certain types of bacteria.