Late adverse reactions to nonionic contrast media.

A prospective study of late adverse reactions to nonionic contrast media was conducted in 2,382 patients who underwent computed tomography (CT). Late reactions were defined as those that occurred more than 30 minutes but within 2 days after completion of CT. The overall rate of late reactions was 8.0% (165 of 2,052 patients), which was greater than the rate of immediate reactions (3.8% [90 of 2,382 patients]). Headache and rash were the most frequent manifestations. Three patients experienced severe vomiting, heavy drowsiness, or oliguria and required medical attention. Late reactions occurred more frequently in female patients, younger adults, and patients with histories of allergic reactions. This investigation shows that although late adverse reactions to nonionic contrast agents are not life threatening, these reactions are not uncommon. It is important that radiologists recognize these late reactions. Patients and referring physicians should be informed that late reactions can occur and may require medical attention.