Radiocontrast agent

Radiocontrast agents used in X-ray examinations can be grouped in positive (iodinated agents, barium sulfate), and negative agents (air, carbon dioxide, methylcellulose). Thorotrast may have been administered to millions of patients prior to being disused. Nonsoluble substances In the past, some non water-soluble contrast agents were used. One such substance was iofendylate (trade names: Pantopaque, Myodil) which was an iodinated oil-based substance that was commonly used in myelography. Due to it being oil-based, it was recommended that the physician remove it from the patient at the end of the procedure. This was a painful and difficult step and because complete removal could not always be achieved, iofendylate's persistence in the body might sometimes lead to arachnoiditis, a potentially painful and debilitating lifelong disorder of the spine. Iofendylate's use ceased when water-soluble agents (such as metrizamide) became available in the late 1970s. Also, with the advent of MRI, myelography became much less-commonly performed. ==Adverse effects==

Modern iodinated contrast agents – especially non-ionic compounds – are generally well tolerated. The adverse effects of radiocontrast can be subdivided into type A reactions (e.g. thyrotoxicosis), and type B reactions (hypersensitivity reactions: allergy and non-allergy reactions [formerly called anaphylactoid reactions]). The documentation of adverse drug reactions to contrast media should be documented precisely so that the patient receives adequate prophylaxis if contrast medium is administered again. Contrast induced nephropathy Iodinated contrast may be toxic to the kidneys, especially when given via the arteries prior to studies such as catheter coronary angiography. Non-ionic contrast agents, which are almost exclusively used in computed tomography studies, have not been shown to cause CIN when given intravenously at doses needed for CT studies. Thyroid dysfunction Iodinated radiocontrast can induce overactivity (hyperthyroidism) and underactivity (hypothyroidism) of the thyroid gland. The risk of either condition developing after a single examination is 2–3 times that of those who have not undergone a scan with iodinated contrast. Thyroid underactivity is mediated by two phenomena called the Plummer and Wolff–Chaikoff effect, where iodine suppresses the production of thyroid hormones; this is usually temporary but there is an association with longer-term thyroid underactivity. Some other people show the opposite effect, called Jod-Basedow phenomenon, where the iodine induces overproduction of thyroid hormone; this may be the result of underlying thyroid disease (such as nodules or Graves' disease) or previous iodine deficiency. Children exposed to iodinated contrast during pregnancy may develop hypothyroidism after birth and monitoring of the thyroid function is recommended. ==See also==