Which medication is contraindicated for administration to a patient who is allergic to penicillin (Pen VK)?

The correct choice is amoxicillin/clavulanate, as it is a type of penicillin and is contraindicated for patients who have a known allergy to penicillin.

Penicillin and its derivatives, including amoxicillin, operate similarly through the inhibition of bacterial cell wall synthesis. An allergy to penicillin typically means that the patient's immune system reacts negatively to the penicillin structure, leading to potential severe allergic reactions such as anaphylaxis or rashes. Since amoxicillin/clavulanate contains amoxicillin, it shares the same core structure that may trigger an allergic response in susceptible individuals.

The other options—cefalexin, doxycycline, and clindamycin—are not structurally related to penicillin and can often be safely prescribed to patients with a penicillin allergy, although clinical judgment is always required. Cefalexin, a cephalosporin, can sometimes cause cross-reactivity in those with penicillin allergies, but the risk is lower when compared to direct penicillin derivatives like amoxicillin. Doxycycline is a tetracycline antibiotic, and clindamycin is a lincosamide, both of which have different mechanisms of action and are generally deemed safe for individuals with pen