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Radiographic Contrast Agents and Contrast Reactions


Mehmet Kocak

, MD, Rush University Medical Center

Last full review/revision Apr 2021| Content last modified Apr 2021
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Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based.

Iodinated contrast agents may be

  • Ionic

  • Nonionic

Ionic contrast agents, which are salts, are hyperosmolar to blood. These agents should not be used for myelography or in injections that may enter the spinal canal (because neurotoxicity is a risk) or the bronchial tree (because pulmonary edema is a risk).

Nonionic contrast agents are low-osmolar (but still hyperosmolar relative to blood) or iso-osmolar (with the same osmolarity as blood). Newer nonionic contrast agents are now routinely used at nearly all institutions because they have fewer adverse effects.

The most serious contrast reactions are

  • Allergic-type reactions

  • Contrast nephropathy (renal damage after intravascular injection of a contrast agent)

Allergic-type contrast reactions

Reactions vary in severity:

  • Mild (eg, cough, itching, nasal congestion)

  • Moderate (eg, dyspnea, wheezing, slight changes in pulse or blood pressure)

  • Severe (eg, respiratory distress, arrhythmias such as bradycardia, seizures, shock, cardiopulmonary arrest)

  • A previous reaction to injected contrast agents

  • Asthma

  • Allergies

Treatment begins by stopping contrast infusion.

For mild or moderate reactions, diphenhydramine 25 to 50 mg IV is usually effective.

For severe reactions, treatment depends on the type of reaction and may include oxygen, epinephrine, IV fluids, and possibly atropine (for bradycardia).

In patients at high risk of contrast reactions, imaging tests that do not require iodinated contrast should be used. If contrast is necessary, a nonionic agent should be used, and patients should be premedicated with prednisone (50 mg orally 13 hours, 7 hours, and 1 hour before injection of contrast) and diphenhydramine (50 mg orally or IM 1 hour before the injection). If patients require imaging immediately, they can be given diphenhydramine 50 mg orally or IM 1 hour before injection of contrast and hydrocortisone 200 mg IV every 4 hours until imaging is completed.

Contrast nephropathy

In contrast-induced nephropathy Contrast Nephropathy Contrast nephropathy is worsening of renal function after IV administration of radiocontrast and is usually temporary. Diagnosis is based on a progressive rise in serum creatinine 24 to 48 hours... read more , serum creatinine typically begins to increase within 24 hours after administration of IV contrast; it peaks between days 3 and 5 and returns to baseline within 7 to 10 days.

Common risk factors include the following:

  • A reduced dose of contrast

  • Use of an iso-osmolar agent

  • Hydration

Many hydration regimens exist; one example is IV administration of 0.9% normal saline at 1 mL/kg for 24 hours beginning a few hours before the procedure.

Acetylcysteine may be given as premedication for patients at risk of developing nephrotoxicity, but its efficacy is uncertain. Oral antihyperglycemic drugs, such as metformin, should be withheld for 48 hours after IV contrast administration to avoid drug accumulation if contrast-induced nephrotoxicity occurs.

Because many protocols dealing with contrast agents and reactions are specific and continually updated, it is important to discuss such details with the imaging department.

Pearls & Pitfalls

  • Withhold oral antihyperglycemic drugs, such as metformin, for 48 hours after IV contrast administration to avoid drug accumulation if contrast-induced nephrotoxicity occurs.

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