Administration of radiographic contrast media in high-risk patients.

Patients with a prior history of an anaphylactoid reaction (AR) to radiographic contrast media (RCM) have an increased risk of an AR during subsequent RCM studies. Based on previous studies in high-risk patients using prednisone or diphenhydramine to reduce the incidence of AR, high-risk patients were treated with a combined prednisone and diphenhydramine protocol in an effort to develop an effective, practical approach to this problem. All patients with convincing histories of AR to RCM with an essential need for a repeat RCM study received 50 mg of prednisone orally every 6 hours for 3 doses ending 1 hour before the RCM study, and 50 mg of diphenhydramine intramuscularly 1 hour prior to the procedure. Resuscitation equipment was readily available. One hundred forty-seven repeat procedures using RCM were carried out in 142 high-risk patients. No serious AR occurred. Two patients had generalized urticaria that resolved in 1 hour. The overall reaction rate in these pretreated high-risk patients was 6.8%, suggesting that this prednisone-diphenhydramine program may be the preferred prophylactic regimen when repeat RCM studies are necessary.