Excretion of contrast media by the immature rabbit. Comparison of Renografin and Iopamidol.

The excretion of iodinated contrast media was studied in 13 immature rabbits after the intravenous injection of 2 ml/kg (approximately 600 mg I/kg) of radio-labelled Renografin-60, a high osmolality agent (1510 mOsm/kg), or Iopamidol-300, a new agent with a much lower osmolality (616 mOsm/kg). Renografin, but not Iopamidol, induced an immediate but transient 40% fall in blood pressure, a marked diuresis that was 3.4 times greater at its maximum than for Iopamidol, and a much lower urinary iodine concentration at the time of maximum diuresis (Renografin: 90.3 +/- 9.2 microgram/ml; Iopamidol: 213 +/- 32.9 microgram/ml). No difference between the two contrast media was found for plasma iodine concentration, renal clearance from the plasma, urinary iodine excretion rate or volume of distribution. In five additional rabbit pups, formal clearance studies made using a constant IV infusion of the agents and timed collections of urine and plasma showed that Iopamidol and Renografin were cleared at the same rate by the kidneys (P greater than 0.9).