Hyper/Hypothyroidism Treatment

Treatment of Hypothyroidism

• Levothyroxine (L-thyroxine) is the standard replacement therapy for hypothyroidism and has all the actions of endogenous thyroxine.
• Liothyronine (T3) is the treatment of choice for myxoedema coma and has all the actions of endogenous triiodothyronine; it is given intravenously.
• Side effects of hypothyroidism treatments include nervousness, heat intolerance, sweating, palpitations, tachycardia, arrhythmias, and unexplained weight loss.
• Hypothyroidism treatments are indicated for myxedema and hypothyroidism.
• Drug interactions with hypothyroidism treatments necessitate increased dosage when taken with estrogen, bile acid-binding resins, Omeprazole, Phenytoin, Carbamazepine, or Propranolol.
• Glucocorticoids reduce the dosage needed for hypothyroidism treatments.

Management of Hyperthyroidism

• Symptomatic treatment for thyrotoxicosis includes beta blockers.
• Treatment of reversible causes includes offending medications like amiodarone and lithium.
• Definitive therapy aims to decrease the synthesis and/or release of T3 & T4.
• Definitive hyperthyroidism therapy options include anti-thyroid drugs thioamides (Methimazole, Propylthiouracil), iodides, and partial or total thyroid removal.

Anti-Thyroid Drugs (Thionamides)

• Methimazole and Propylthiouracil (PTU) are used to decrease the synthesis and/or release of thyroid hormones.
• Thionamides inhibit the synthesis of thyroid hormones T3 and T4 by inhibiting peroxidase enzyme, which catalyzes the iodination of tyrosine residues in thyroglobulin.
• PTU blocks the conversion of T4 to T3 within the thyroid and in peripheral tissues.

Propylthiouracil Vs. Methimazole

• Propylthiouracil and Methimazole are both rapidly absorbed from the GIT.
• Protein binding for Propylthiouracil is 80-90%, with most of the drug being free, while most of the Methimazole drug is free.
• Propylthiouracil is excreted by the kidneys as an inactive metabolite within 24 hours.
• Methimazole is excreted slowly, with 60-70% of the drug excreted in 48 hours.
• The half-life of Propylthiouracil is 1.5 hours, whereas Methimazole has a longer half-life of 6 hours.
• Methimazole is given once daily.
• Propylthiouracil is recommended in pregnancy due to being less crossing placenta (protein bound).
• Methimazole is not recommended in pregnancy.
• Both Propylthiouracil and Methimazole are secreted less in breast milk.
• Graves' disease is the most common cause of hyperthyroidism.

Notes on Anti-Thyroid Drugs

• If agranulocytosis occurs (severe leukopenia, most commonly neutropenia), discontinue the anti-thyroid drug and administer appropriate antibiotics.
• For hyperthyroidism in pregnant women, PTU is given in the 1st trimester, while methimazole is given in the 2nd and 3rd trimesters.

Iodide

• Lugol's solution and potassium iodide block thyroid hormone release.
• Iodide inhibits thyroid hormone synthesis and release, and blocks the peripheral conversion of T4 to T3.

Iodide Indications

• Iodide is indicated prior to thyroid surgery to decrease vascularity & size of the gland.
• Iodide is indicated following radioactive iodine therapy and for thyrotoxicosis.
• The effect of iodide is not sustained and produces a temporary remission of symptoms.

Iodide Side Effects

• Iodide side effects include sore mouth and throat, swelling of the tongue, ulcerations of mucous membranes, and a metallic taste in the mouth.
• Iodide may produce iodism, characterized by swelling of salivary glands, mucous membrane ulceration, metallic taste, bleeding disorders, and rarely anaphylaxis.
• Iodide should not be used as a single therapy or in pregnancy.

Thyroid Removal by Radioactive Iodine or Surgery

• Failure to achieve euthyroidism with antithyroid drugs, and high surgical risk are indications for radioactive iodine (131I) treatment.
• Large goiter, obstructive symptoms like dyspnea, and dysphagia are indications for surgery.
• Sub-total thyroidectomy is the treatment of choice for very large glands or multinodular goiter.

Symptomatic Treatment for Hyperthyroidism

• Beta-blockers are effective in treating thyrotoxicosis symptoms.
• Propranolol is the most widely studied and used
• Beta-blockers provide adjunctive therapy to relieve adrenergic symptoms like tremor, palpitation, heat intolerance, and nervousness.
• Examples of beta-blockers are Propranolol, Atenolol, and Metoprolol.
• Propranolol is contraindicated in asthmatic patients.
• Patients who cannot tolerate beta-blockers may be treated with calcium channel blockers like diltiazem.

Thyroid Storm

• Thyroid storm involves extreme symptoms of hyperthyroidism and is a medical emergency.
• Treatment is similar to hyperthyroidism, but drugs are given in higher doses and more frequently.
• A sudden acute exacerbation of all symptoms of thyrotoxicosis that presents itself as a life threatening syndrome.
• This sudden acute exacerbation of all symptoms of thyrotoxicosis leads to hypermetabolism and excessive adrenergic activity.
• Death may occur due to heart failure and shock.

Thyroid Storm Management

• Initial steps of management include a hydration treatment.
• Hydration, potassium iodide 10 drops orally daily, Propylthiouracil 250 mg orally every six hours (or 400 mg every six hours rectally), hydrocortisone 50 mg IV every 6 hours to prevent shock, and Beta-blockers are all therapy components.

Thyrotoxicosis During Pregnancy

• It is better to start therapy before pregnancy with radioactive iodine (131I) or subtotal thyroidectomy to avoid acute exacerbation during pregnancy.
• During pregnancy, radioiodine is contraindicated.
• Propylthiouracil is the drug of choice during pregnancy.