TMP-SMX and creatinine

Q: Trimethoprim-sulfamethoxazole (TMP-SMX) (bactrim) increases the serum creatinine by which method? (select one)

A) increasing the muscle breakdown (high CPK)

B) decreasing the tubular secretion of creatinine

Answer: B

(TMP-SMX) decreases the tubular secretion of creatinine, which reflexly can make clinicians believe that the patient is in renal failure. This rise in serum creatinine is not a true renal failure. 

In contrast, hyperkalemia associated with TMP-SMX is real and can be fatal. This has been found particularly true in patients with HIV (high dosage use), on angiotensin-converting enzyme (ACE) inhibitors, or on angiotensin receptor blockers (ARB). 

Other side effects can be renal tubular acidosis, hepatitis, hypoglycemia, hyponatremia, and hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency. It should be given with caution in patients with folate deficiency.

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References;

1. Masters PA, O'Bryan TA, Zurlo J, et al. Trimethoprim-sulfamethoxazole revisited. Arch Intern Med 2003; 163:402.

2. Ho JM, Juurlink DN. Considerations when prescribing trimethoprim-sulfamethoxazole. CMAJ. 2011 Nov 8;183(16):1851-8. doi: 10.1503/cmaj.111152. Epub 2011 Oct 11. PMID: 21989472; PMCID: PMC3216436.