Trimethoprim-sulfamethoxazole (TMP-SMX), which is structurally similar to amiloride, causes hyperkalemia by blocking the apical membrane sodium channel in the principal cell (similar to amiloride and triamterene). Significantly, hyperkalemia occurs with high-dose TMP-SMX in patients with AIDS and with standard-dose TMP-SMX in patients with mild renal impairment. Adrenal insufficiency is more classically associated with hyperkalemia, hyponatremia, and hypotension. The level of hyperkalemia in this patient is excessive for the modest change in serum creatinine, which is elevated from the effect of trimethoprim to competitively inhibit proximal tubular creatinine secretion.
- Trimethoprim-sulfamethoxazole therapy.
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