Changes in serum magnesium during excretory urography. A comparison of ionic and nonionic contrast media.

It is known that ionic contrast media (CM) bind magnesium and that patients with asthma often benefit from magnesium injections. Similarly, asthmatics have a higher incidence of CM reactions. This work tests the hypothesis that ionic CM alter serum magnesium more than nonionic CM. Ten patients were divided into two groups; one group received iothalamate and the other received iohexol. The total magnesium level changed significantly from baseline in the iothalamate-treated group (P less than .01). Iothalamate produced a significant decrease in protein-bound magnesium (P less than .01) with a significant increase in filterable magnesium (P less than .01). Iohexol did not produce significant changes for any of the magnesium fractions. The patient with the most clinically significant adverse reaction (though minor) had the lowest baseline magnesium level. Further studies with larger groups including patients with asthma are needed.