Iohexol

Iohexol is a nonionic, water-soluble iodinated contrast agent used to enhance the visibility of vascular and tissue structures during radiographic examinations. It is a low-osmolar contrast agent designed to reduce the osmotic burden on patients compared with older ionic agents, helping to lower the risk of certain adverse reactions. Iohexol is supplied in several concentrations and administered by injection either intravenously or intra-arterially, depending on the diagnostic procedure.

Medical uses include computed tomography (CT) and various forms of angiography, urography, and myelography. The choice of concentration, route of administration, and dosing depends on the clinical indication, patient factors such as weight and organ function, and the imaging technique being used. The agent is distributed in the extracellular space and is excreted primarily by the kidneys.

Pharmacokinetics and metabolism: Iohexol is not significantly metabolized and is largely excreted unchanged in the urine. In individuals with normal renal function, the plasma half-life is typically about two hours; in renal impairment, clearance is reduced and the half-life is prolonged. Hydration and baseline kidney function influence clearance and risk of renal-related adverse effects.

Safety and precautions: Potential adverse effects include hypersensitivity or anaphylactoid reactions, nausea, vomiting, dizziness, flushing, and local injection-site reactions. Serious events, including contrast-induced nephropathy, are more likely in patients with preexisting renal impairment, diabetes, dehydration, or advanced age. Extravasation at the injection site can cause tissue injury. Caution is advised in patients with a history of iodide allergy. In pregnancy, use is weighed against potential benefits. When metformin is used, clinicians often withhold it around the time of contrast administration and for a period afterward if renal function is reduced.

See also: iodinated contrast media, contrast-induced nephropathy.