A 47-year-old man with known HIV infection is admitted for shortness of breath and non-productive cough. He has not been adherent with his medications and has not received medical attention for two years. His other medical problems include hepatitis C, lower extremity neuropathy, and tonic-clonic seizures. His last seizure episode was 7 years ago. He receives 2 L of intravenous normal saline in the emergency department and is started on trimethoprim-sulfamethoxazole and prednisone for presumed pneumocystis pneumonia.
Forty-eight hours later, his serum creatinine increased from 1.3 to 1.6 mg/dL.
His temperature is 37.8 C (100 F), blood pressure is 102/70 mm Hg supine and 105/68 mm Hg standing, and pulse is 112/min. He has crackles in both posterior lung bases. His liver is palpated 2 cm below the costal margin. There is no peripheral edema.
Urinalysis results are shown below:

Which of the following is the most likely cause of his elevated creatinine?

Question

A 47-year-old man with known HIV infection is admitted for shortness of breath and non-productive cough.  He has not been adherent with his medications and has not received medical attention for two years.  His other medical problems include hepatitis C, lower extremity neuropathy, and tonic-clonic seizures.  His last seizure episode was 7 years ago.  He receives 2 L of intravenous normal saline in the emergency department and is started on trimethoprim-sulfamethoxazole and prednisone for presumed pneumocystis pneumonia.
Forty-eight hours later, his serum creatinine increased from 1.3 to 1.6 mg/dL.
His temperature is 37.8 C (100 F), blood pressure is 102/70 mm Hg supine and 105/68 mm Hg standing, and pulse is 112/min.  He has crackles in both posterior lung bases.  His liver is palpated 2 cm below the costal margin.  There is no peripheral edema.
Urinalysis results are shown below:

Which of the following is the most likely cause of his elevated creatinine?

Quizplus · Accepted Answer

Creatinine is an organic cation, and approximately 15% of urinary creatinine comes from tubular secretion. Other organic cations and anions, such as trimethoprim and cimetidine, can compete with creatinine for tubular secretion. By decreasing creatinine secretion, both trimethoprim and cimetidine can result in increased serum creatinine without decreasing the glomerular filtration rate (GFR). This increase is usually minor, in the range of 0.1-0.2 mg/dL, but can be up to 0.4-0.5 mg/dL. Other factors that can increase the serum creatinine without decreasing GFR include chemical interference by ketone bodies, cefoxitin, and flucytosine. (Choice A) AIDS nephropathy is typically associated with significant proteinuria, which is not seen in this patient. (Choice B) Interstitial nephritis is usually associated with more white cells and granular casts on urinalysis. Drug-induced early interstitial nephritis may also present with a rash, fever, eosinophilia, and eosinophiluria. (Choice C) Volume depletion with pre-renal injury causes enhanced renal tubular sodium conservation and a spot urinary sodium < 20 mEq/dL. This patient does not have orthostatic blood pressure changes and has a spot urinary sodium of 40 mEq/dL. (Choice D) Sulfamethoxazole crystalluria usually takes longer to develop, occurs in the setting of more acidic urine, and is often associated with the appearance of sulfa crystals in the urine. Educational objective: By decreasing creatinine secretion, both trimethoprim and cimetidine can result in an increased serum creatinine without decreasing the glomerular filtration rate. __________ References: Renal effects of trimethoprim in cyclosporine- and azathioprine-treated kidney allograft patients. (http://www.ncbi.nlm.nih.gov/pubmed/2677807) Trimethoprim-sulfamethoxazole revisited. (http://www.ncbi.nlm.nih.gov/pubmed/12588198)

A 47-Year-Old Man with Known HIV Infection Is Admitted for Shortness