Trimethoprim-sulfamethoxazole （TMP-SMX） is the first-line treatment for the prevention of pneumocystis pneumonia （PCP）; however, discontinuations due to side effects are common. Although package inserts and guidelines describe the appropriate dosage, the dosage for patients with immunologic renal diseases remains unclear.

The aim of this study was to survey the tolerability of low-dose TMP-SMX for the prevention of PCP in patients with immunological kidney disease. We included patients prescribed TMP-SMX for the prevention of PCP in immunological kidney disease between April 2016 and March 2024. Patients were divided into two groups according to the dose of TMP-SMX: a control dose group （four tablets/week） and low-dose group （two tablets/week）. We investigated the cumulative incidence of PCP and the cumulative discontinuation rate of TMP-SMX.

The study included 75 patients （10 in the control dose group and 65 in the low-dose group）. During the observation period, neither group experienced PCP, and the cumulative discontinuation rate of TMP-SMX, adjusted for competing risks, at 180 days was 30.0% （95% confidence interval 0.071-0.578） in the control group and 15.37% （95% confidence interval 0.075-0.259） in the low-dose group. The adjusted hazard ratio for the low-dose group compared with the control group was 0.397 （95% confidence interval 0.110-1.438, p = 0.160）.

The low-dose group had fewer discontinuations of TMP-SMX than the control dose group; however, the difference was not significant. The findings from this retrospective study suggest that low-dose TMP-SMX for preventing PCP in patients with immunologic kidney disease may offer better tolerability and a safer profile.

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Patients with chronic kidney disease who have impaired kidney calcium excretion are susceptible to calcium overload -induced hypercalcemia. However, hypercalcemias resulting from fosfomycin calcium hydrate (FOM-Ca) remain unknown. Therefore, this report presents a case of hypercalcemia suggested by FOM-Ca in a patient with chronic kidney disease a living -donor kidney allograft recipient. The patient, a woman in her 40s, underwent a living donor kidney transplant from her mother when she was 25 years old. Her Scr level was approximately 1.70 mg/dL. The patient was admitted to the hospital due to infectious enteritis and initiated on FOM-Ca 2 g/day. Although she recovered from the enteritis, her serum calcium and Scr levels increased from 10.6 mg/dL and 1.69 mg/dL at admission to 12.1 mg/dL and 1.93 mg/dL on the fifth day of hospitalization, respectively. Given the impaired baseline renal function of the patient, we initially investigated the possibility of exogenous calcium or vitamin D overload as the differential diagnosis of hypercalcemia. Drug-induced hypercalcemia caused by FOM-Ca was speculated; therefore, FOM-Ca administration was discontinued. Serum calcium and Scr levels improved to 10.7 mg/dL and 1.66 mg/dL, respectively, on the 10th day of hospitalization. When administering FOM-Ca to patients with chronic kidney disease and impaired calcium–parathyroid hormone balance, monitoring serum calcium concentration is essential. This is crucial owing to the potential risk of developing hypercalcemia from calcium loading.

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