Product selection criteria for intravascular ionic contrast media.
The chemistry, clinical use, pharmacokinetics, adverse reactions, dosages, and formulary recommendations for intravascular ionic contrast media routinely used in radiologic procedures are reviewed. The meglumine, sodium, or combined meglumine-sodium salts of triiodinated benzoic acid derivatives, diatrizoic and iothalamic acid, are commonly used as intravascular ionic contrast media for radiographic visualization of blood vessels and the urinary tract. Meglumine salts of iodoxamate and iodipamide are used for intravenous cholangiography. The iodine in the contrast medium is responsible for the absorption of x-rays and the resulting opacification of the organ system or other area under investigation. Adverse reactions to intravascular ionic contrast media broadly include hypersensitivity and chemotoxic reactions. The incidence of major life-threatening hypersensitivity reactions, such as severe hypotension, cardiac arrhythmias or arrest, pulmonary or laryngeal edema, and convulsions, is estimated at 0.01-0.1% of the population receiving these agents. Dose- and concentration-dependent chemotoxic reactions result from the direct effects of the contrast medium on the blood vessels or organs being perfused. The meglumine salts of diatrizoic acid and iothalamic acid are less toxic in the cerebral circulation than sodium salts; hence, diatrizoate meglumine or iothalamate meglumine are recommended for cerebral angiography. In coronary angiographic examinations, combined meglumine and sodium (6.6 parts meglumine to 1 part sodium) formulations of diatrizoate are recommended because they consist predominantly of the meglumine salt with minimal but adequate amounts of sodium to prevent ventricular fibrillation. Predominantly meglumine salts of diatrizoic and iothalamic acid are also used for peripheral angiography, computerized tomography, and digital subtraction angiography. The dosages of ionic contrast media vary considerably depending on the nature of the radiological examination, the respective technique employed, and the age and condition of the patient. The cost differences between diatrizoate and iothalamate media are typically minimal. Formulary recommendations regarding the appropriate chemical nature of these media are based on the reported adverse reactions with these agents.