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THYROID & ANTITHYROID DRUGS

HYPOTHYROIDISM
1. Synthetic T3 and T4
  1. Levothyroxine
    1. Drug of choice
    2. allergy rare
  2. Liothyronine (L-T3)
    1. More potent than levothyroxine
    2. multiple daily doses needed
    3. Greater cardiotoxicity
    4. expensive
  3. EFFECTS
    1. increase sympathetic
    2. Tachycardia, increase cardiac output, hypertension, arrhythmias
HYPERTHYROIDISM
1. ANTITHYROID AGENTS
  1. THIOAMIDES
    1. Methimazole & Propylthiouracil (PTU).
      1. concentrated in the thyroid
    2. MOA
      1. inhibit thyroid peroxidase
        Inhibit oxidation of iodide into iodine
        Inhibit formation of MIT & DIT
    3. USES
      1. moderate hyperthyroidism
    4. ADVERSE
      1. Maculopapular skin rashes
      2. fever, hepatitis, lupus-like syndrome
  2. IODIDE SALTS (POTASSIUM IODIDE)
    1. MOA
      1. inhibit the release of thyroid hormones from thyroid gland
      2. reduce size and vascularization of the hyperplastic gland
      3. Oral
        Cross placenta
        withdrawal may produce severe thyrotoxicosis
    2. USES
      1. Initiation therapy
      2. thyroid storm (thyrotoxicosis)
    3. ADVERSE
      1. sore mouth and throat
      2. Goiter (fetus)
      3. skin rashes (acneiform)
  3. SODIUM IPODATE
    1. Iodinated contrast agents (x-ray film)
    2. MOA
      1. rapidly inhibit the conversion of T4 to T3 in liver, kidney, pituitary gland and brain.
    3. Use
      1. thyroid storm
    4. non-toxic
  4. ANION INHIBITORS
    1. Perchlorate (Clo4-), thiocyanate (SCN-)
    2. MOA
      1. block uptake of iodide by thyroid gland through competitive inhibition
    3. Use
      1. iodide-induced hyperthyroidism
    4. Side Effects
      1. toxic, aplastic anemia (rarely used).
  5. RADIOACTIVE IODINE (RAI) 131 I
    1. Sodium 131I orally
    2. MOA
      1. concentrated in thyroid, beta particle emission → destroys thyroid tissues
      2. cross placenta, excreted in milk
        contraindicated in pregnancy or lactation
    3. USES
      1. thyrotoxicosis
THYROTOXICOSIS IN PREGNANCY
1. Propylthiouracil (PTU) throughout pregnancy
THYROID STORM
1. life threatening syndrome
2. propanolol – IV → decrease severe CVS manifestations
3. Potassium Iodide (10 drops orally) → reduce release of thyroid hormone
4. PTU- reduces thyroid hormones synthesis. - inhibit peripheral deiodination of T4 toT3.
5. Steroid (hydrocortisone) protect patients against shock.
Treatment aims

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THYROID & ANTITHYROID DRUGS

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	Created by Zulhilmi Zainal over 10 years ago