A 29-year-old woman has had a fever and sore throat for the past 3 days. On physical examination, her temperature is 38degC. The pharynx is erythematous, with yellowish tonsillar exudate. She is treated with ampicillin and recovers fully in 7 days. Two weeks later, she develops fever and a rash and notices a slight decrease in urinary output. Her temperature is 37.7degC, and there is a diffuse erythematous rash on the trunk and extremities. Urinalysis shows a pH of 6; specific gravity, 1.022; 1+ proteinuria; 1+ hematuria; and no glucose or ketones. Microscopic examination of the urine shows RBCs and WBCs, including eosinophils, but no casts or crystals. What is the most likely cause of her disease?
A 29-year-old woman has had a fever and sore throat for the past 3 days. On physical examination, her temperature is 38degC. The pharynx is erythematous, with yellowish tonsillar exudate. She is treated with ampicillin and recovers fully in 7 days. Two weeks later, she develops fever and a rash and notices a slight decrease in urinary output. Her temperature is 37.7degC, and there is a diffuse erythematous rash on the trunk and extremities. Urinalysis shows a pH of 6; specific gravity, 1.022; 1+ proteinuria; 1+ hematuria; and no glucose or ketones. Microscopic examination of the urine shows RBCs and WBCs, including eosinophils, but no casts or crystals. What is the most likely cause of her disease?
💡 Explanation
## **Core Concept**
The patient's presentation suggests an allergic reaction occurring two weeks after the initiation of ampicillin for a presumed bacterial pharyngitis. The development of fever, rash, and renal abnormalities (proteinuria, hematuria, and presence of eosinophils in the urine) points towards an immune-mediated condition.
## **Why the Correct Answer is Right**
The clinical scenario described is highly suggestive of **ampicillin-induced hypersensitivity reaction**, specifically **interstitial nephritis**. This condition is characterized by inflammation of the renal interstitium and tubules, often triggered by medications such as antibiotics (e.g., ampicillin, methicillin), NSAIDs, and others. The presence of eosinophils in the urine (eosinophiluria) is a key diagnostic clue. The patient's symptoms of fever, rash, and renal involvement (slight decrease in urinary output, proteinuria, hematuria) are consistent with this diagnosis.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Without specific details on the option, we cannot directly address its incorrectness, but given the context, it's unlikely to relate directly to drug-induced interstitial nephritis.
- **Option B:** Similarly, without specifics, we can't directly refute, but the clinical picture provided doesn't align with typical presentations of conditions not related to drug hypersensitivity reactions.
- **Option C:** This option is not provided, but typically, conditions not related to hypersensitivity reactions or direct nephrotoxicity wouldn't present with this constellation of symptoms.
- **Option D:** Assuming this is not the correct answer, any condition not directly related to an allergic or hypersensitivity reaction to ampicillin would not fit the clinical scenario.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **drug-induced interstitial nephritis** often presents with the classic triad of **fever, rash, and renal dysfunction**. The presence of **eosinophiluria** is a significant diagnostic clue. This condition is a well-known complication of certain medications, including penicillins like ampicillin.
## **Correct Answer:** D. Acute interstitial nephritis.
✓ Correct Answer: D. Hypersensitivity reaction to ampicillin
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