Hypothyroidism refers to the common pathological disorder of thyroid hormone deficiency. The successful therapy for hypothyroidism is levothyroxine (LT4) administration, which is the same as thyroxine but produced synthetically. Serum thyrotropin (TSH) normalization with LT4 replacement therapy in hypothyroidism is generally needed to restore a euthyroid state. The daily dose of thyroxine therapy depends on various factors, such as body weight, age, and severity. It also differs from hypothyroidism during pregnancy to congenital hypothyroidism. The presence of various comorbidities may exist such as myxoedema coma, coronary artery disease, obesity, anemia and COVID-19 which necessitate individualized treatment. LT4 intolerance manifested with sympathetic hyperactivity may appear during the first hours after the LT4 administration. It requires starting with very low doses of LT4 that should be increased gradually, and reaching normal TSH may take several months. The sympathetic hyperactivity may be attributable to the presence of uncorrected iron-deficiency anemia that worsens by the use of thyroid hormone.
Part of the book: Hypothyroidism