Health Sciences Authority (HSA) would like to bring to the attention of healthcare professionals, rare overseas cases of hypothyroidism following iodinated contrast media (ICM) exposure, particularly in full term and preterm infants. If left untreated, this might result in severe delays in growth and development, including mental development. As such, thyroid function evaluation and monitoring for infants exposed to ICM is recommended, with initiation of treatment for abnormal thyroid function, if needed.
ICM products are generally used to enhance visualisation of vascular structures and organs during radiographic procedures such as angiography and computed tomography. As ICM products contain iodine, they may interfere with thyroid hormone production, which may in turn affect proper growth and development (including mental development) in infants and proper metabolic activity in children and adults.
Hypothyroidism following ICM administration might be attributed to the Wolff-Chaikoff effect, an autoregulatory mechanism whereby a large amount of ingested iodine acutely inhibits thyroid hormone synthesis within the follicular cells. In most individuals, the decreased production of thyroid hormones is transient and resumes after adaptation to the Wolff-Chaikoff effect (known as an “escape” phenomenon). However, certain susceptible populations, such as infants (especially those born preterm), the elderly and those with pre-existing thyroid disease, might be at an increased risk of failure to escape from the Wolff-Chaikoff effect, leading to development of iodine-induced thyroid dysfunction.
There are 21 ICM products registered locally since 1991, comprising nine active ingredients namely, iopamidol, iohexol, ioversol, iopromide, iomeprol, meglumine ioxitalamate, iodixanol, iobitridol, and ethyl esters of iodised fatty acids of poppy-seed oil.
To date, HSA has not received any local adverse drug reaction reports of thyroid dysfunction associated with the use of ICM. The Singapore package inserts for ICM products will be updated on the warnings regarding ICM-induced thyroid function changes. Healthcare professionals are advised to evaluate and monitor thyroid function in infants exposed to ICM.
Please refer to the following website in HSA for details:
http://www.hsa.gov.sg/content/hsa/../iodinated-contrastmediaandriskofhypothyroidismparticularlyininfa.html
In Hong Kong, there are 27 registered pharmaceutical products which belong to ICM products, including iopamidol (2 products), iohexol (2 products), ioversol (4 products), iopromide (2 products), iomeprol (4 products), meglumine ioxitalamate (3 products), iodixanol (2 products), iobitridol (6 products), iodised oil (1 product) and mixture of meglumine ioxaglate and sodium ioxaglate (1 product), and all products are prescription-only medicines. So far, the Department of Health (DH) has received 2 cases of adverse drug reaction related to iopromide, and 4 cases related to iobitridol, but these cases are not related to hypothyroidism. DH has not received any case of adverse drug reaction related to other ICM.
Related news was previously issued by the United States Food and Drug Administration (FDA) and Health Canada, and was posted on the Drug Office website on 18 Nov 2015 and 25 Apr 2017. Letters to inform local healthcare professionals of the risk of hypothyroidism were issued by DH on 18 Nov 2015. In Apr 2016, the Registration Committee of the Pharmacy and Poisons Board discussed the matter and had decided that warnings on the risk of hypothyroidism should be included in ICM products. DH will remain vigilant on safety update of the drugs issued by other overseas drug regulatory authorities.
Ends/Wednesday, Sep 19, 2018
Issued at HKT 16:00
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