Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which drug is known to cause a rash in patients with mononucleosis?

1. Amoxicillin

2. Azithromycin

3. Ciprofloxacin

4. Metronidazole

The correct answer is: Amoxicillin

Amoxicillin is known to cause a rash in patients with mononucleosis, particularly those infected with Epstein-Barr virus (EBV). The reason this occurs is that a significant percentage of patients with mononucleosis who are treated with amoxicillin develop a characteristic diffuse rash. This adverse effect is often attributed to the complex immune response triggered by the viral infection when the drug is administered, rather than a direct allergic reaction to amoxicillin itself. This association underscores the importance of avoiding amoxicillin for treating patients diagnosed with mononucleosis unless absolutely necessary. Instead, healthcare providers may choose other antibiotics, particularly if a bacterial co-infection is suspected, to minimize the risk of rash and other complications. The other medications listed, such as azithromycin, ciprofloxacin, and metronidazole, do not have the same established link to rash development in the context of mononucleosis, making amoxicillin the primary concern in this scenario.