Some nephrologists make alterations in routine peritoneal and
hemodialysis schedules after diagnostic studies that use radiographic
contrast agents. A study to determine the pharmacokinetics of one
contrast agent,
iothalamate, is reported. The plasma (total body) clearance of
iothalamate was measured in seven patients who had endstage renal disease (
ESRD) and who received maintenance
hemodialysis. During an interdialytic period, plasma clearance of
iothalamate varied from 0.7 to 5.2 mL/min (3.1 +/- 1.8 mL/min, mean +/- SD) with an elimination rate constant (beta) of 0.0164 +/- 0.01 hr-1, a terminal half-life of 61 +/- 42 hours, and an estimated distribution volume of 11 +/- 3.9 L.
Hemodialysis clearance of
iothalamate was 104 +/- 54 mL/min. With the assumption that
iothalamate is mainly distributed in the extracellular fluid (ECF) compartment, the theoretical fluid shift from the intracellular fluid (ICF) compartment to the ECF compartment was 323 mL after administration of the largest dose (2.1 mL/kg or 1.6 mmol/kg of
body weight) of 60%
meglumine iothalamate solution. The average maximum serum osmolarity change was less than expected, suggesting some type of internal buffering of
meglumine iothalamate. In the first few hours after radiocontrast administration in four patients, the average change in serum osmolarity was 5 mmol/L; the average change in serum
sodium concentration during this same time was a decrease of 0.5 mmol/L. The minor increase in ECF volume induced by hyperosmolar
contrast agents does not require immediate dialysis in most patients. When needed, however, for contrast-related adverse effects,
hemodialysis is efficient in rapidly removing
iothalamate.