Absence of Iodine/Iodide in Cough/Expectorant Medications: A True Disclaimer or not?

Sir,

Iodine is an essential micronutrient required by all individuals for health and well-being. Iodine serves a crucial role in thyroid physiology by being both a key component of thyroid hormones and by regulating thyroid gland function. The thyroid gland concentrates iodine by an adenosine triphosphate-dependent carrier-mediated mechanism against an electrochemical gradient, and this process is regulated by thyroid-stimulating hormone (TSH). TSH stimulates while excess iodine inhibits all the consequent steps in thyroid hormone biosynthesis, from oxidation and organification of iodide to the secretion of thyroxine and tri-iodothyronine into the circulation.[1]

Radioactive iodine (I¹³¹) is selectively taken up by thyroid, incorporated into iodoamino acids, and deposited in the follicular colloid. The thyroid follicles then gradually and slowly release I¹³¹. I ¹³¹emits destructive beta particles from within the follicles causing damage to only thyroid parenchymal cells with minimal influence on surrounding tissue.[1] I ¹³¹is mainly used in the ablation of residual thyroid/metastasis following total thyroidectomy in patients with well-differentiated thyroid cancer. It is also indicated in the treatment of hyperthyroidism in older patients and in those with heart disease, persistent or recurrent Graves' disease after subtotal thyroidectomy, and failure of remission following prolonged treatment with anti-thyroid drugs and in patients with toxic nodular goiter.[12]

During therapy with I¹³¹, patients are recommended to avoid/discontinue the use of iodide-containing preparations, iodine supplements, and other medications that could potentially affect the ability of thyroid tissue to accumulate I ¹³¹for a sufficient time before commencing therapy.[23]

Among the medications containing iodide, are cough/expectorants which are always recommended to be avoided during I ¹³¹therapies. The real question now arises if cough and expectorant medications truly contain iodide. With extensive search in relation to this regard, it was discovered that few of the older cough/expectorant preparations contained iodide/iodine in substantially large quantities, but preparations of the recent times claim not to contain iodine except for one preparation.

Table 1 summarizes a few important constituents of cough/expectorant combinations prevalent during the late 19^th centuries containing iodide. The table also shows some commonly used cough/expectorant combinations during the recent 20^th century exhibiting a striking feature of lacking any iodide component in them with one exception.[34]

Table 1 Cough expectorant/mucolytic combinations and their compositions

This preliminary initiative of insight into the iodine/iodide content among the various cough and expectorant medications currently available in contrast to the older preparations may prove valuable to consider precautionary measures during I ¹³¹therapy to avoid potentially significant drug interactions, where presently, all cough/expectorant medications are contraindicated with an assumption of high iodide content in them.