Contrast-induced nephropathy is a serious complication of intravascular x-ray contrast agents. The osmolality of the contrast medium is an important fact in contrast-induced nephropathy and should ideally be iso-osmolar to blood. Today, nonionic contrast agents are state of the art for vascular use, the ionic contrast agents caused more adverse reactions.
Signs of contrast-induced nephropathy after the application of vascular contrast agents are a serum creatinine increase of 0.5 mg/dL (In the United States, creatinine is typically reported in mg/dL, while in Canada and Europe µmol/L may be used. 1 mg/dL of creatinine is 88.4 µmol/L) or an increase of serum creatinine greater than 25%.

A higher risk of contrast-induced nephropathy is associated with:
The use of a nonionic contrast agent, iso-osmolar to blood and a low dose reduces the risk for contrast-induced nephropathy.

Adverse reactions on contrast agents are rare, but like all other pharmaceuticals, contrast media are not completely without side effects.
Adverse effects to contrast media include allergic symptoms, anaphylactoid reactions, chemotoxic reactions, idiosyncratic reactions, contrast-induced nephropathy, iodide-induced hyperthyroidism and local tissue damage. An adverse reaction can be related to dose, the toxicity, and the physio-chemical properties of the contrast agent, for example osmolality, viscosity, and hydrophilicity.
Side effects such as a metallic taste in the mouth, generalized warmth or flushing, nausea and vomiting, increase with rapid flow and large volume of the injected agent. Although venous tolerance is usually good, there have been reports of sensation like burning, stinging or numbness and of venospasm.

Characterization of adverse reactions include:

(LOCM) Low-osmolar contrast media have a wide range of indications due to their lower side effects. The type of contrast media is an important risk factor for an adverse reaction.
LOCM have not completely replaced contrast media with higher osmolality due to their higher cost. Guidelines of professional organizations give recommendations for the selective use of low-osmolar contrast media for certain high-risk patients.
There are ionic and nonionic iodinated contrast materials with low osmolality available:
An adverse reaction occurs in low-risk patients who receive conventional ionic contrast agents more often than in high-risk patients who receive nonionic LOCM.

See also Contrast Enhancement, Biliary Contrast Agents, Safety of Contrast Agents and Contrast-Induced Nephropathy.

Radiographic contrast media (RCM) contributes important information to the diagnostic process. Actual contrast agents are safe drugs. Adverse reactions are rare, the incidence and severity of side effects decrease with the use of nonionic and low-osmolar contrast media. Adverse reactions are diverse, ranging from mild physiological disturbances to very rare life-threatening anaphylactic or anaphylactoid reactions. Users of contrast agents must be aware of the risk factors and be prepared to promptly manage adverse effects.
Side effects that may occur with intravascular administration of contrast agents are also possible after administration by other paths. Increased risk to an adverse reaction includes patients with a history of a previous reaction to a contrast medium, a known sensitivity to iodine, or a known clinical hypersensitivity (bronchial asthma, hay fever, and food allergies).

See also Contrast-Induced Nephropathy, Iodide-Induced Hyperthyroidism and Idiosyncratic Reactions.