Endocrine Pharmacology II - Thyroid Hormones
- Thyroid agents
- Thyrotropin RH -> Thyroid SH -> T3 + T4
- Dopamine and somatostatin inhibit TSH
- Levothyroxine (T4) and Liothyronine (T3) are used to treat hypothyroidism
- Thioamides, Iodide, and Beta Blockers treat hyperthyroidism
- Low thyroid hormone most commonly caused by Iodine deficiency
- Hashimoto's thyroiditis is most common cause of hypothyroidism in US
- Low thyroid hormone -> manifests as thick lips, large tongue, malocclusion, impacted mandibular molars
- T3 = Triiodothyronine, T4 = Thyroxine
- Levothyroxine is DOC for low thyroid -> long half-life (7 days), converted to T3 intracellularly
- Can cause bone maturation, nervousness, heat intolerance
- Inhibited absorption by soy, bran, and coffee
- Liothyronine is synthetic T3 - more potent than levothyroxine, but only preferred for short term TSH suppression
- Liotrix (combination T3 and T4) and dessicated thyroid sometimes used
- Myxedema is a type of hypothyroidism that often coincides with coronary artery disease
- Amiodarone can induce hypothyroidism from rT3 production
- Hyperthyroidism is more common in women than men
- Hyperthyroidism can cause facial osteoporosis, BMS, accelerated dental eruption
- Thioamides include methimazole and propylthiouracil (PTU), and inhibit a peroxidase reaction that converts Iodine to TH
- Methimazole 10x more potent than PTU, but PTU also inhibits peripheral deiodination of T3 and T4
- Nausea, GI distress, and altered taste or smell occur as side effects for thioamides
- Anion inhibitors - perchlorate, pertechnetate, and thiocyanate block Iodide uptake
- I-131 treats thyrotoxicosis by destroying thyroid parenchyma, contraindicated in pregnant women as it can pass through the placental barriers
- Iodides (potassium Iodide and Lugol's solution) were commonly used prior to thioamides, and are contraindicated in pregnancy
- Hyperthyroidism increases sensitivty to Warfarin, decreases sensitivity to cardiac glycosides
- PTU is safe in first trimester, but otherwise both thioamides are contraindicated in pregnancy
- Beta blockers control cardiovascular issues in thyrotoxicosis
- Graves' Disease - antibodies against TSH receptor sites