Final answer:
The 18-year-old female likely has infectious mononucleosis, which commonly causes a rash and a worsening of symptoms upon administration of the antibiotic Ampicillin, suggesting a hypersensitivity reaction.
Step-by-step explanation:
An 18 year old white female presenting with a febrile illness, sore throat, and lymphadenopathy was prescribed Ampicillin. After taking the medication, she developed a rash and her condition worsened. This could suggest a hypersensitivity reaction to the antibiotic, which is common with ampicillin especially if the underlying cause of the symptoms is infectious mononucleosis. Patients with mononucleosis who are treated with ampicillin often develop a rash. In such a scenario, the antibiotic should be stopped and the patient should be evaluated again to confirm the diagnosis and manage accordingly.