Thyroid and Anti-Thyroid Drugs
Anatomy and Physiology of the Thyroid GlandMember of the Endocrine System Secretes thyroid hormones, such as thyroxine and calcitonin, which regulate metabolism and growth. Composed of epithelial cells specialize in the absorption of iodine and secretion of thyroid hormones.
Synthesis of Thyroid Hormones
Mechanism of Thyroid Hormone Activation in Body. Thyroxin crosses the cell membrane passively and enters the nucleus Deiodinase cleaves the iodine at position 5 to yield triiodithronine (T3)
TH Effects on Metabolism
Thyroxin increases the body’s basal metabolic rate, BMR, to maintain electrochemical gradient in cell.Stimulates carbohydrate metabolism and lipolysis, or the break down of fats.Affects protein synthesis.Increases the body’s sensitivity to cathecholamines, i.e. adrenalineHypothyroidism
Insufficient amount of thyroid hormone synthesized causing lethargy and weight gain, brady cardia, poor resistance to cold ,mental & physical slowing.In children mental retardation & dwarfism..Treatment for Hypothyroidism
Hormone replacement therapyLevothyroxine—Synthetic T4Liothyronine—Synthetic T3Liotrix—Combination of synthetic T4 and T3Treatment for Hypothyroidism (con,t)
Because thyroid hormones serve to increase heart rate, T4, the inactive form, is typically administered to older patients who have an increased risk for heart attack on account of their age. Synthetic T3 is reserved for younger patients, who do not have a history of heart problems and for individuals non-responsive to T4 treatment.Adverse reactions
Hyperthyroidism-like features Cardiovascular toxicity (arrhythmias, angina, and infarction) CNS stimulation, insomnia, nervouness, heat intolerance & weight loss.Hyperthyroidism
The over production of thyroid hormones. Symptoms include fatigue, weight lose, rapid heart beat, anxiety, swollen eyes, and hot intolerance ,tremor , nervousness.Drugs used in hyperthyroidism
Thiouracil PropylthiouracilMethimazoleCarbimazole─Degraded to methimazole in the bodyRadioactive IodineThiouracil
Inhibits thyroid hormone synthesis by irreversibly binding to thyroid peroxidase inhibiting the attach of iodine to the tyrosine residue of thyroglobulin. Effective in the long-term treatment of hyperthyroidism. 6-8 weeks before maximum effect of the drug achieved. Since thyroxin storage needs two weeks to be depleted in the thyroid glandSide Effects
Include headache, nausea, vomiting, itchy skin and rash, and muscle aches and pains. Serious liver damage, agranulocytosis and vaculitis Administering too high a dosage of anti-thyroid drugs can cause hypothyroidism. All cross the placenta so they teratogenic, but PTU is safer because its high protein binding.Radioactive iodine (131I)
Rapidly taken, then is incorporated into thyroglobulin. Leads to partial or total destruction of the gland by emission of beta particles. Damage to surrounding tissue is minimal.