Extrarenal effect of cyclosporine A on potassium homeostasis in renal transplant recipients.

Cyclosporine A (CyA) is known to cause hyperkalemia by impairing renal potassium excretion. However, the observation of transient and severe hyperkalemia occurring within 3 to 5 hours of CyA ingestion in several organ transplant patients led us to postulate that it might also cause a potassium efflux from the intracellular to the extracellular fluid space. We tested this hypothesis by studying 22 nondiabetic, renal transplant patients with stable renal function (serum creatine < 2.25 mg/dL) who were treated with CyA (CyA group; n = 14) or imuran and prednisone (STD group; n = 8). Eight CyA and four STD patients also were treated with a beta-blocker (BB). While at rest, fasting plasma potassium levels were sampled hourly in all patients from 8:00 am to 1:00 pm. All medications (including CyA and BBs) were given after the 8:00 am blood sampling. Venous pH, osmolality, insulin, aldosterone, epinephrine, norepinephrine, and CyA levels also were determined at 8:00 am, 11:00 am, and 1:00 pm. Urine was collected from 11:00 pm to 8:00 am prior to the study (period I) and from 8:00 am to 1:00 pm during the study (period II) for measurement of potassium excretion (standardized to a 5-hour period). A significant increase in serial plasma potassium levels was noted in the CyA + BB group only (P = 0.0006 by repeated measures analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)