Effects of Patiromer on Pharmacokinetics of Immunosuppresive Drugs in Renal Transplant Recipients

Patiromer lowers potassium effectively in patients with hyperkalemia and chronic kidney disease. Patients with a kidney transplant usually have reduced renal function and may also develop hyperkalemia. However, potential interactions between immunosuppressive medications and patiromer have not been evaluated. These interactions could involve change in AUC of immunosuppressive drugs, such as calcineurin inhibitors or mycophenolate, or increased risk of hypomagnesemia, since both tacrolimus and patiromer have this potential side effect. We wish to evaluate potential interactions to ensure safe use of this drug in the transplant population.

Patients with a kidney transplant may develop hyperkalemia. This could be due to different mechanisms. In some patients it could be due to reduced kidney function. In others, it could be secondary to renal tubular acidosis type 4 caused by necessary medications used after transplantation. The most important medicines contributing to hyperkalemia after kidney transplantation are calcineurin inhibitors which are a compulsory part of the immunosuppressive regimen, ACE inhibitors or ARBs in patients with hypertension, and trimethoprim-sulfa, which is used as infection prophylaxis in all patients during the first 6 months after transplantation. In the weeks after renal transplantation around 5-10% of transplant patients at our institution at some point develop hyperkalemia above the limit where some type of management of hyperkalemia would be indicated. As the drugs mentioned above can rarely or not at all be withdrawn after transplantation, most doctors will either observe the hyperkalemia untreated or try to lower the potassium level. In outpatients with s-potassium of 5 - 6.5, urgent management is usually not necessary. However, some kind of intervention is still indicated, to make sure that the potassium will decrease during the next days. Patiromer could be an interesting alternative in those kidney transplanted patients that are in this category. We are not aware of any published studies describing the use of patiromer in the transplant population. We intend to investigate if there is any pharmacokinetic interaction between patiromer and immunosuppressive drugs affecting the blood concentration of the latter.