Iothalamate

Iothalamate is an iodinated, water-soluble contrast medium used to enhance radiographic visualization during diagnostic imaging. It is an ionic, high-osmolar contrast agent employed in procedures such as intravenous urography, CT angiography, and conventional angiography, as well as fluoroscopic studies of the urinary tract. Prepared in salt forms, most commonly iothalamate meglumine or iothalamate sodium, it is administered by intravenous or intra-arterial injection, depending on the exam. Historically, it was also used intrathecally for myelography, but this practice has declined due to safety concerns and the availability of safer alternatives.

Iothalamate is eliminated primarily by the kidneys, with clearance proportional to renal function. Its ionic, high osmolar properties can cause adverse effects including a warm flushing sensation, nausea, vomiting, or a metallic taste. More serious risks include hypersensitivity reactions and contrast-induced nephropathy, particularly in patients with pre-existing renal impairment, dehydration, diabetes, or high-dose exposure. It is contraindicated in individuals with known iodinated contrast allergy or severe renal failure. Careful patient selection, pre-procedure hydration, and avoidance of nephrotoxic medications reduce risk. Premedication may be used for patients with prior mild hypersensitivity; facilities should monitor during and after administration.

Because of toxicity concerns and the development of lower-osmolar and iso-osmolar contrast agents, the use of iothalamate has declined in modern practice in favor of newer agents; however, it remains listed in some older practice guidelines and is still used in certain regions or cases where alternatives are not available.