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1 From the Departments of Radiology (U.N., B.E., P.L., T.A.) and Radiation Physics (M.N.), University of Lund, Malmö University Hospital, Malmö, Sweden; and Nycomed Innovation, Medeon, Malmö, Sweden (K.G.). Received August 29, 2001; accepted September 5. Address correspondence to U.N., Röntgenavdelningen, Lasarettet, SE-231 85 Trelleborg, Sweden (e-mail: ulf.nyman@skane.se). 2 9*: Vascular system, location unspecified.
Index terms: Angiography, contrast media, 9*.1211 • Contrast media, complications • Contrast media, effects • Contrast media, toxicity • Iodine and iodine compounds • Gadolinium • Uremia
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INTRODUCTION |
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However, we oppose their statement that with gadolinium-based contrast media in doses of less than 0.3–0.4 mmol/kg, there is "a decreased incidence of contrast medium–induced nephropathy, as compared with similar volumes of iodinated contrast material" (1). Simply reporting the volume without stating the concentration of iodinated medium used makes any comparison with gadolinium-based media meaningless. Iodinated contrast media are, in fact, commercially available in concentrations varying from 140 to 400 mg of iodine per milliliter (mg I/mL), a difference with a factor of almost three.
The sole purpose of injecting contrast medium in angiography is to visualize blood vessels. Therefore, the main question is what are the nephrotoxic effects of various contrast media that provide the same diagnostic information? Thus, any comparison regarding nephrotoxic effects between contrast media during angiography should be made at equal-attenuating concentrations and doses. No such comparative data have been presented by Spinosa et al or others, who advocate the use of gadolinium-based media in patients with azotemia. We also have not been able to find reports of any prospective randomized studies in which the nephrotoxicity of equal-attenuating doses of iodinated and gadolinium-based contrast media were compared.
According to the article by Spinosa et al (1), the attenuation of a 0.5 mol/L gadolinium chelate is equivalent to that of 75–150 mg I/mL at 96 kV in experiments with a 20-cm water phantom. However, no attenuation measurements were presented, and their figure 1b presents only a visual comparison. In addition, the mode of radiologic technique, digital angiography or computed tomography (CT), and the x-ray tube filtration are not defined. The appearance of the phantom indicates to us that they may have used CT. If that is the case, because CT x-ray tubes generally have more filtration than those of angiographic equipment, beam hardening results in increased image contrast for gadolinium-enhanced images relative to that of iodine-enhanced images. The attenuation for a 0.5 mol/L gadolinium chelate then may very well be in the range of that for 75–150 mg I/mL. We have recently repeated our experiments in which we exposed 20-mL syringes filled with contrast medium in a 20-cm water phantom and used a different digital angiographic unit with 6.3-mm aluminum filtration. We again found that the attenuation for a 0.5 mol/L gadolinium chelate corresponded to that for 60–80 mg I/mL in the 70–90 kV range. We also point out that if the voltage had been kept low (eg, close to 70 kV) in the experiment performed by Spinosa et al, the iodine concentration that was equally attenuating with 0.5 mol/L gadolinium chelate would definitely have been much closer to 75 than 150 mg I/mL.
If, however, we accept our divergent opinions on what represents an equal-attenuating concentration, a 0.5 mol/L solution of gadolinium-based contrast medium may give the same diagnostic information as an iodinated medium at a concentration of 60–150 mg I/mL when imaging in the 72–96-kV range. A maximum safe dose of 50 mL of 0.5 mol/L gadolinium chelate in a 70-kg person (0.3–0.4 mmol/kg), as advocated by Spinosa et al, would then still correspond to iodine doses as low as 3.0 (50 x 60 mg) to 7.5 (50 x 150 mg) g of iodine. These doses are equivalent to only 10–25 mL of a "full-strength" iodinated medium with a concentration of 300 mg I/mL. Also note that the maximum dose approved by the U.S. Food and Drug Administration for intravenous use of gadolinium varies and is only 0.1 mmol/kg for 0.5 mol/L gadopentetate dimeglumine, or 14 mL in a 70-kg person. This dose corresponds in attenuation to a total iodine dose of 0.84–2.10 g (14 x 60–150 mg), or about 3–7 mL of medium with a concentration of 300 mg I/mL.
Spinosa et al do not refer to another important aspect of contrast medium–induced nephrotoxicity in angiography: namely, the osmolality of the contrast medium solutions. Apart from the low iodine dose needed to obtain the same angiographic diagnostic information as with gadolinium-based media, nonionic mono- and dimeric iodinated contrast media can be obtained as solutions isotonic to plasma at all concentrations between 60 and 150 mg I/mL. The 0.5 mol/L gadolinium chelate solutions of today are all hypertonic, with an osmolality two to seven times that of human plasma. Nor do Spinosa et al stress the large difference in osmolality between various gadolinium-based media when selecting among those for angiography in patients with azotemia.
Spinosa et al also state in their conclusion that "[t]he overall safety profile of gadolinium-based contrast media is excellent." We point out that nonionic monomeric iodinated media in the 60–150 mg I/mL range have lower general toxicity than do 0.5 mol/L gadolinium-based media, according to results of median lethal dose studies in mice. If the equal-attenuating concentration of iodinated media is about 60–70 mg I/mL, then median lethal dose results in mice indicate that the toxicity of gadolinium chelates is six to 25 times higher than that of iodinated media. If the equal-attenuating concentration of iodinated media is about 120–150 mg I/mL, then the toxicity of gadolinium chelates is three to 12 times that of iodinated media.
In summary, we believe the review by Spinosa et al does not present sufficient evidence that the hypertonic gadolinium-based contrast media of today are safer with regard to nephrotoxicity than those low concentrations and doses of isotonic nonionic mono- or dimeric iodinated contrast media that are needed to yield the same angiographic diagnostic information. Our arguments indicate that iodinated contrast media may in fact represent a lower toxic load on the body than equal-attenuating doses of gadolinium-based media.
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