Hyperthyroidism beta-blockers

As the symptoms of hyperthyroidism mimic in many aspects those of sympathic stimulation propranolol, and probably also other non-selective beta blockers (see Chapter 20), give rapid relieve in thyrotoxicosis while having no effect on the underlying disease. 

Beta blockers without intrinsic sympathomimetic activity (eg, metoprolol, propranolol, atenolol) are effective therapeutic adjuncts in the management of thyrotoxicosis since many of these symptoms mimic those associated with sympathetic stimulation. Propranolol has been the 3 blocker most widely studied and used in the therapy of thyrotoxicosis. Beta blockers cause clinical improvement of hyperthyroid symptoms but do not typically alter thyroid hormone levels. Propranolol at doses greater than 160 mg/d may also reduce T3 levels approximately 20% by inhibiting the peripheral conversion of T4 to T3. 

A 48-year-old woman developed palpitation and insomnia. The clinical history, physical examination, and laboratory tests supported hyperthyroidism. Since July 1994 she had been combating constipation by improper use of an iodine-containing antiseptic cream for external use only. She had inserted povidone-iodine into her rectum by means of a cannula. The iodine-containing cream was withdrawn and she was given a beta-blocker. The palpitation resolved within 2 weeks and her plasma thyroid hormone concentrations normalized within 1 month. 

Keck FS, Loos U, Duntas L, Pfeiffer EF. Hyperthyreosis factitia acuta—Geringe klinische Symptome bei drei Fallen unter beta-Blocker-Behandlung. [Acute factitious hyperthyroidism—moderate clinical symptoms in 3 cases under beta-blocker treatment.] Klin Wochenschr 1986 64(7) 319-26. 

Although iodide is effective in treating hyperthyroidism for short periods, the effects of this drug begin to diminish after about 2 weeks of administration.35 Consequently, iodide is used in limited situations, such as temporary control of hyperthyroidism prior to thyroidectomy. In addition, iodide may cause a severe hypersensitive reaction in susceptible individuals. Therefore, the use of iodide has been replaced somewhat by other agents such as antithyroid drugs and beta blockers. 

Patients with severe hyperthyroidism can have an occult cardiomyopathy that makes them extremely sensitive to beta-blockers. The long duration of action of sotalol in this case necessitated prolonged inotropic and vasopressor support. A shorter-acting beta-blocker, such as esmo-lol, could theoretically be safer in such cases. 

Adrenaline is contraindicated in cases of diabetes, hyperthyroidism, serious heart arrhythmias and coronary insufficiency or in combination with beta-blockers or monoamine oxidase (MAO) inhibitors. Lidocaine with adrenaline has a very rapid onset of action. Its duration of action is longer than that of lidocaine without adrenaline. However, inadvertent injection of a lidocaine-adrenaline solution into the vessels located near the nerve trunks increases the heart rate (immediate sinus tachycardia at over 130 beats per minute, spontaneously reversible in around 15 minutes) and increases ventricular excitability (risk of fibrillation). It can trigger angina attacks that may lead to a heart attack. It is therefore preferable not to use adrenaline before a full-face phenol peel. 

Answer E. Increased sympathetic activity is a major problem in hyperthyroidism and is best managed by use of beta blockers, which can offset cardiac stimulatory effects. Propranolol has an ancillary action in thyrotoxicosis in that it prevents conversion of T4 to T3 via its inhibition of 5 deiodinase. Amiodarone causes difficult-to-predict adverse effects on thyroid function and would not be appropriate in a patient with hyperthyroidism. Bretylium is an IV agent reserved for ventricular arrhythmias. Digoxin is not ideal because of its complex actions on the heart, which include both inhibition and stimulation. 

Nonselective beta-blocker prototype local anesthetic action but no partial agonist effect. Used in HTN, angina, arrhythmias, migraine, hyperthyroidism, tremor. Tox asthma, AV block, CHF. 

Both alpha- and beta-adrenoceptors are blocked by labetalol Glucagon can be useful in reversing cardiac depression caused by a beta blocker They mask the signs of developing hyperthyroidism Treatment of glaucoma commonly involves the topical use of propranolol... 

Until the patient becomes biochemically euthyroid or hypothyroid, which usually takes 6-12 weeks after treatment, symptoms of hyperthyroidism can be controlled using beta-blockers (Becker and Hurly, 1971 Refetoff et ai, 1977 Ross et ai, 1983). The use of SSKI or Lugols solution started 1 week after the administration of radioactive iodine will also attenuate biochemical hyperthyroidism and not adversely affect the outcome of radioiodine therapy (Ross et ai, 1983). In some patients, transient biochemical hypothyroidism can develop by 8 weeks, and hyperthyroidism will recur (Aizawa et ai, 1997). In 5-20% of patients (varying with dose), hyperthyroidism will persist a second dose of radioiodine is recommended for these patients (Levy et ai, 1988). Additional doses of radioactive iodine are not usually given until 6 months after initial therapy. 

Beta-adrenoceptor antagonists are used in the treatment of hyperthyroidism to alleviate symptoms but are not considered to influence thyroid hormone production nor the effect of the hormone on cell function. A study of the effect of beta-blockers on lymphocyte metabolism was done with the purpose to clarify their mechanism of action in hyperthyroidism [68]. When hyperthyroid subjects were treated with beta-blockers, lymphocyte heat production was found to be within normal limits, thus showing that beta-blockers prevent the expected increased of cell metabolism under stimulation of thyroid hormone. These results seem to indicate that increased thermogenesis in hyperthyroidism is mediated via adrenergic receptors, rather than via nuclear thyroid hormone receptors. 

It should also be noted that beta-blockers (e.g. pro-panolol) are indicated in hyperthyroidism for relief of some of the symptoms such as increased heart rate, tremor, etc. 

Beta-adrenoceptor blockers represent a very important group of drugs used in the treatment of several cardiovascular diseases and hyperthyroidism. Sometimes their use is limited by the occurrence of side effects, such as fatigue in the lower extremities, general tiredness the pathogenesis of these symptoms is unclear. 

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