*Purpose: Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice for Pneumocystis jirovecii pneumonia (PJP) prophylaxis in kidney transplant recipients (KTRs), however, it can be complicated by hyperkalemia. Study aims were to assess the number of KTRs who discontinued TMP-SMX as an intervention for hyperkalemia within 6 months (mos) post-op vs those who did not, and to describe risk factors for hyperkalemia in both groups.

*Methods: This IRB approved single-center retrospective case-control analysis included KTRs who were: ≥ 18 yrs, HIV negative, transplanted at our center Jan 2019-Jan 2020, initiated on tacrolimus (TAC) immunosuppression and TMP-SMX PJP prophylaxis at transplant, and had ≥ 6 mos follow-up. Hyperkalemia (defined as ≥ 2 consecutive serum potassium levels ≥ 5 mEq/L) was assessed at defined time-points: 1 week (wk), 2 wks and monthly for 6 mos post-op.

*Results: This interim analysis included 100 of 200 KTRs. Overall, the majority of KTRs were male (60%), Caucasian (55%) and were deceased donor KTRs (58%). Glomerulonephritis was the primary cause of kidney failure in 27% of KTRs. TMP-SMX was discontinued in 23 KTR and held in 2 KTR (25% overall) within 6 mos post-op. Hyperkalemia was the reason for holding/discontinuing TMP-SMX in 8% of KTRs. The overall hyperkalemia incidence was 38%. Evaluated time-point where hyperkalemia was most commonly first experienced was 2 wks post-op (40% of KTRs). When comparing earlier vs later evaluated time-points, hyperkalemia occurred more frequently early on [(87%) KTRs with hyperkalemia first identified at 1 wk-2 mos vs 3-6 mos (13%), p =0.001]. A significant risk factor for hyperkalemia was pre-existing diabetes mellitus (DM) with an additional numeric trend for post-transplant DM (Table 1). There were no differences in delayed graft function (DGF) or low eGFR at wk 2 between groups (Table 1), or at other timepoints (data not shown). One yr graft loss occurred in 5 KTRs (5%) with death being the cause in 1 KTR.

*Conclusions: 1) TMP-SMX, considered first-line PJP prophylaxis, was held/discontinued in a quarter of KTRs overall, with hyperkalemia being the reason in < 10% of KTRs. 2) Hyperkalemia occurred in almost 40% of KTRs, and most commonly occurred in the first 2 wks post-op. 3) A significant risk factor for hyperkalemia was pre-existing DM with a numeric trend for post-transplant DM. Data collection is ongoing, and will include data on use of potassium lowering therapies.

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