Postmarketing surveillance studies of gadolinium contrast agents worldwide have all demonstrated an extremely low incidence of adverse drug reactions. The precise number of reactions varies among papers and particular contrast formulations, but nearly all can be characterized as very mild, with aggregate incidence <2.5%. Examples of such minor reactions include nausea, vomiting, headache, a metallic taste, injection site discomfort, warmth, paresthesias, and dizziness. Such rates are not too much higher than those occurring during placebo injection of saline and are about one-third as common as reaction rates recorded with nonionic iodine-based contrast media.
Immediate hypersensitivity reactions occur in approximately 1 in 1000 cases, usually within 1 hour of contrast administration. These are more likely in patients with allergies, asthma, and prior reaction to gadolinium contrast. The most common of these reactions are mild pruritus (itching) and urticaria (hives). Prior reaction to gadolinium contrast confers an 8-fold higher risk for a future reaction, often more severe than the first.
Moderately severe hypersensitivity reactions (including bronchospasm, laryngospasm, facial edema, tachycardia, arrhythmias, or widespread urticaria) occur in about 1 in 5000 cases. Seizures induced directly by MR contrast agents in epileptic patients have been reported, but are too rare to represent a contraindication for the use of these drugs in evaluating patients with seizures.
Worldwide, a number of severe anaphylactoid reactions to gadolinium-based MR contrast agents, including death, have been reported. The incidence of such severe reactions is about 1 in 400,000.
“All things are poison and nothing is without poison, only the dose permits something not to be poisonous.” – Paracelsus
The above discussion describes general adverse physiologic and allergic-like events and does include special situations (including use in pregnancy, infancy, and renal insufficiency). These important topics each have devoted Q&A's.
In conclusion, although the gadolinum-based MR contrast agents are extremely safe, they are not infinitely so. One should always remember that administration of any drug carries with it the risk of a life-threatening reaction as we as the difference between liner and cyclic chemical structures in gadolinium shall be considered.