Drugs that suppress TSH or cause central hypothyroidism

Drugs that suppress TSH or cause central hypothyroidism

Abstract. Many different drugs affect thyroid function. Most of these drugs act at the level of the thyroid in patients with normal thyroid function, or at the level of thyroid hormone absorption or metabolism in patients requiring exogenous levothyroxine. A small subset of medications including glucocorticoids, dopamine agonists, somatostatin analogs and rexinoids affect thyroid function through suppression of TSH in the thyrotrope or hypothalamus. Fortunately, most of these medications do not cause clinically evident central hypothyroidism. A newer class of nuclear hormone receptors agonists, called rexinoids, cause clinically significant central hypothyroidism in most patients and dopamine agonists may exacerbate ‘hypothyroidism’ in patients with nonthyroidal illness. In this review, we explore mechanisms governing TSH suppression of these drugs and the clinical relevance of these effects.

Keywords: TSH, Central hypothyroidism, Medications, Thyroid function, Glucocorticoids, Dopamine, Somatostatin, Rexinoids

Summary. Many drugs and medications can affect thyroid function, but only a small subset (glucocorticoids, dopamine agonists, somatostatin analogs and rexinoids) suppress TSH at the level of the hypothalamus or pituitary. Fortunately, the widely used glucocorticoids and the somatostatin analogs do not induce clinically evident central hypothyroidism even after prolonged high dose use. Dopamine agonists do not cause clinically significant central hypothyroidism, but may have an additive effect of TSH suppression in patients with nonthyroidal illness, which may lead to a state of iatrogenic central hypothyroidism in this patient population. Rexinoids, clearly induce clinically significant central hypothyroidism in most patients, who require levothyroxine replacement and monitoring of serum free T4 levels. As this newer class of drugs may be used in more patients (advanced cancer, metabolic disorders, dermatologic disorders), clinicians need to be aware of this unique and treatable side-effect.

Table 1 Drugs known to affect thyroid function in patients with an intact hypothalamic-pituitary-thyroid axis
Table 2 Drugs that affect thyroid function in patients taking levothyroxine
Table 3 Drugs that suppress TSH and proposed mechanisms of action

• Footnotes.
• Most drugs that suppress serum TSH (glucocorticoids, dopamine agonists, somatostatin analogs) do not cause clinically significant hypothyroidism
• Metformin may affect thyroid function tests and TSH levels in patients on exogenous levothyroxine. Monitoring of TSH and free T4 levels is advised for patients taking both metformin and levothyroxine.
• Rexinoids, which are used in certain cancers, suppress serum TSH in most patients and cause clinically significant central hypothyroidism. Careful monitoring of TSH and free T4 levels is important.

Kilde/les mer: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2784889/