DISCUSSION: 
Our patient has undergone a renal transplant for stage 5 chronic kidney disease and was already on hemodialysis for the past 1 year. The preoperative, intraoperative course was fair with no significant concerns. The early postoperative course of the patient was satisfactory. As a part of prophylaxis to Pneumocystis jiroveci and Cytomegalovirus in solid organ transplant, we have started Cotrimoxazole (TMP-SMX) and Valganciclovir respectively from postoperative day-5. On day-10, the serum Potassium was 6.0 mEq/L and increased to 6.2 mEq/L by day 11. The serum creatinine was 2.86 mg/dl on day-0 and 2.11 mg/dl on day-1 which returned to the normal range by day-3. On day-10 and 11, levels of serum creatinine were 0.54 mg/dl and 0.66 mg/dl respectively which were in the normal range, signifying normal renal function. Though the serum urea levels of the patient were consistently higher than the normal range (6-24 mg/dl), the BUN/Cr ratio was consistently higher than 20. We attributed it to inadequate hydration as the creatinine was normal. We gave intravenous fluids judiciously as he is a known patient of ischemic heart disease. He is not on any other drugs that could cause hyperkalemia except Cotrimoxazole (TMP-SMX). Trimethoprim inhibits sodium transport in the apical membrane of the distal nephron, reducing the transepithelial voltage causing decreased potassium secretion, similar to amiloride.2 A study conducted by Rana M Al AdAwi et al about the incidence of cotrimoxazole-induced hyperkalemia in tertiary care showed 28% regardless of interacting drugs and 33% without interacting drugs. 3 Though hyperkalemia by TMP-SMX is common in patients with renal insufficiency, it can even occur in patients with normal renal function4 and with standard dose5. Similarly, More AS et al presented a case of TMP-SMX induced hyperkalemia in renal transplant6. Serum potassium levels are monitored regularly in patients receiving TMP-SMX in the long term, especially in at-risk patients because the serum levels may rise even higher than 6.5 mEq/L6. Following the observation of hyperkalemia in this patient, Cotrimoxazole has been withheld from day 11 as well as the Potassium chloride syrup that he has been receiving since day 6. The effect of potassium chloride syrup on hyperkalemia in this patient was ruled out since he is receiving a standard dose from 4 days prior to the observation with a normal range of daily serum potassium levels. The study of R Alagappan et al showed a statistically significant increase in serum potassium levels in patients after 5 days of treatment with TMP-SMX.7 The patient was treated with intravenous fluids and potassium binders in the hospital from day 11-13 in addition to withholding TMP-SMX and potassium chloride syrup. In addition to routine discharge medications, he was discharged with potassium binders twice daily until the next follow-up. The follow-up serum potassium levels showed 4.2 mEq/L.