Intravenous trimethoprim–sulfamethoxazole desensitization as a therapeutic strategy for late-onset Pneumocystis jirovecii pneumonia in a kidney transplant recipient: a case report

BACKGROUND: Pneumocystis jirovecii pneumonia is a potentially fatal opportunistic infection in kidney transplant recipients under intensified immunosuppression. Although most cases occur within the first post-transplant year, late-onset infections may develop after rituximab therapy or discontinuation of prophylaxis. Trimethoprim-sulfamethoxazole is the preferred agent for prevention and treatment, but allergy or intolerance limits its use. Desensitization protocols may allow reintroduction of this drug in selected patients. CASE PRESENTATION: A 37-year-old white female kidney transplant recipient presented with progressive dyspnea and deteriorating renal function 9 years after receiving a living donor kidney transplant from her brother. She had Alport-syndrome-related nephrotic syndrome and chronic kidney disease and had been treated for chronic antibody-mediated rejection with pulse corticosteroids, intravenous immunoglobulin, and rituximab. Pneumocystis jirovecii pneumonia prophylaxis was omitted because of a prior trimethoprim-sulfamethoxazole allergy. On admission, serum creatinine was 4.97 mg/dL, C-reactive protein was 56 mg/L, and chest computed tomography revealed diffuse ground-glass opacities. Other infectious causes were excluded. A presumptive diagnosis of Pneumocystis jirovecii pneumonia was made, and intravenous trimethoprim-sulfamethoxazole was given using a graded desensitization protocol, starting with a 1:1000 dilution and gradually increasing every 30-60 minutes. No hypersensitivity reactions occurred. Clinical improvement was observed within 1 week, and follow-up imaging showed near-complete resolution of pulmonary infiltrates. CONCLUSION: This case shows that late-onset Pneumocystis jirovecii pneumonia may develop years after transplantation, particularly after rituximab therapy and without prophylaxis. Intravenous trimethoprim-sulfamethoxazole desensitization can be a safe and effective therapeutic option for transplant recipients with a trimethoprim-sulfamethoxazole allergy, enabling use of the optimal antimicrobial agent.