**8.6. β- blockers**

β- blockers do not affect the synthesis or secretion of thyroid hormones. Many of the symptoms & signs of thyrotoxicosis are due to hypersensitivity of the sympathetic nervous system to thyroid hormones. Thus use of β- blockers in thyrotoxicosis, improve the signs and symptoms mediated by the sympathetic nervous system. Tachycardia, palpitation, tremor, anxiety, excess sweating, lid retraction improves with β- blockers. Propranolol has additional advantage over other β- blockers. It inhibits the peripheral conversion of T4 to T3. β- blockers reduce cardiac output without altering oxygen consumption, can have adverse effect in liver, where the arteriovenous oxygen difference is already elevated in the hyperthyroid state. Propranolol is most commonly used agent but other β- blockers can also be used. It is used in a dose of 20-60 mg every 6-8 hours. Short acting agents like esmolol is used for intravenous purpose. Long acting agents like atenolol or metoprolol are used for prolonged treatment. β- blockers should be rapidly tapered and discontinued once stable euthyroidism it achieved.
