Impact of thrice-weekly cotrimoxazole prophylaxis on creatinine and potassium plasma levels in kidney transplant recipients

Introduction: Cotrimoxazole (CTX) 800/160 mg daily or thrice-weekly is recommended as prophylaxis of Pneumocystis jiroveciipneumonia in kidney transplant recipients. Cotrimoxazole 800/160 daily elevates plasma creatinine and potassium levels but whether the thrice-weekly regimen does so is unknown. Methods: Medical records of 225 kidney transplant recipients at Cliniques Universitaires Saint-Luc were analyzed retrospectively. All received thrice-weekly CTX 800/160 for 6 months after transplantation. Monthly laboratory results, co-medications, and tacrolimus trough levels were compared. Standard statistical tests were used. Results: One month after CTX stop, creatinine level decreased by 0.11 mg/dl (8%, p = 0.029). This contrasts with its stability in previous and subsequent months. No co-medication change accounted for this decrease. The decrease averaged 0.17 mg/dl (p &lt; 0.01) in the highest initial creatinine tertile. The higher the initial creatinine level, the greater the decrease after CTX stop (p &lt; 0.001), and urea levels remained stable after CTX stop. Potassium levels decreased by 0.09 mmol/L (p = 0.021) one month after CTX stop, and decreased by 0.23 mmol/L (p &lt; 0.01) in the highest initial potassium level tertile. Conclusions: Our study pinpoints the impact of CTX 800/160 thrice-weekly on creatinine and potassium levels in kidney transplant recipients. This should be considered when interpreting the evolution of plasma creatinine over time, especially in patients with graft dysfunction. Thus, creatinine levels of cohorts with 6 months versus lifelong CTX require different interpretations. Graphical abstract: <fig id="Figa" position="anchor"> <graphic position="anchor" specific-use="HTML" mime-subtype="PNG" href="MediaObjects/40620_2023_1773_Figa_HTML.png" id="MO1"></graphic> </fig>