Contrast media and glomerular filtration: dose dependence of clearance for three agents.

Determination of plasma clearance of contrast agents has been advocated as a means to assess glomerular filtration rate. To evaluate the feasibility of different agents for this purpose, we have compared, in healthy volunteers, the dose dependence of plasma clearance for three contrast media (iohexol, a nonionic agent, and iothalamate and metrizoate, which are ionic substances), with special emphasis on the lower dose range (2-20 mL corresponding to 0.9-12.9 g, depending on dose and agent). Iohexol and iothalamate were cleared at constant rates, irrespective of given dose, whereas metrizoate clearance increased significantly at lower doses. In general, the clearances or iothalamate and metrizoate were, respectively, moderately and markedly higher than that of iohexol. The clearance of different doses of metrizoate (2 mL versus a radiographic dose of 40 mL or more) was also compared with the clearance of [51Cr]EDTA in two groups of patients with reduced renal function. When compared with [51Cr]EDTA in patients with renal dysfunction, metrizoate was cleared significantly faster after a 2-mL dose, whereas clearances were identical when the metrizoate dose was 40 mL or more. These findings indicate that tubular secretion plays an active role in the elimination of metrizoate. The pharmacokinetic properties of iohexol, in combination with its low toxicity, make it a suitable agent for determination of glomerular filtration rate in clinical practice.

Excretion of iohexol and metrizoate in human breast milk.

Six lactating women undergoing contrast media examination had milk and blood taken to determine the rate and extent of excretion of iohexol (Omnipaque) (four mothers) and metrizoate (Isopaque) (two mothers). Blood samples were taken up to 45 minutes and milk samples up to 48 hours after the contrast medium injection. The excretion was low, reaching a maximum at 3 to 6 hours and showing a slow decay curve (t1/2 = 15 to 108 hours). One mother, who was weaning her baby, showed a different excretion pattern. The amount excreted during 24 hours was about 0.5 per cent of the weight adjusted maternal dose for both iohexol and metrizoate. It is not likely, that such a low dose of poorly absorbed drug would cause any adverse effects in the infant, unless it is hypersensitive to the drug already. The authors consider breast feeding to be acceptable for mothers receiving iohexol or metrizoate.