Chapter 31 Thyroid and Antithyroid

Question 1

Thyroid Augmentation Drugs

Answer 1

• Levothyroxine; Eltroxin or Synthroid ( T4 - preferred drug). Preferred drug because its hormonal content is standardized.
• Work the same way as endogenous thyroid hormones: Metabolic rate (lipid, carbs, protein); increase O2 Consumption, temp, blood volume , and cell growth; increase myocardial β receptors (increase cardiac output); increase kidney blood flow (GFR; diuretic effect)
• Never discontinue abruptly
• Give same time each day to maintain consistent blood levels
• Take in am to decrease insomnia
• DO NOT INTERCHANGE BRANDS! Brands are not equivalent in dosing

Question 2

Contraindications, adverse effects, and interactions of Thyroid Augmentation Drugs

Answer 2

• Contraindications include: MI, Adrenal insufficiency, hyperthyroidism
• Adverse Effects include: Cardiac dysrhythmia with the risk for fatal irregularities, Insomnia, tremors, headache, anxiety, Nausea diarrhea, appetite changes, cramps, Weight loss, menstrual irregularities, sweating, heat intolerance, fever
• Interactions include: Enhance warfarin so reduce dose, Reduce digoxin and insulin so increase, Increased sensitivity to epinephrine, and Cholestyramine (calcium and aluminum bind in GI tract and reduce absorption both drugs)

Question 3

Pharmacokinetics of Thyroid Augmentation Drugs

Answer 3

• Onset 2 days
• Peak 3-4 weeks
• Duration 1-3 weeks
• Half life average is 7 days (min is 3-5 days and max is 9-10 days)
• More then 99% protein bound so it stays in the body longer and increases the risk for toxicity

Question 4

Antithyroid drugs

Answer 4

• Thioamide derivatives
• Inhibits iodine which impedes thyroid hormone function
• Propylthiouracil (can also inhibit the conversion of T3 to T4)
• Used to palliate hyperthyroidism and to prevent the surge in thyroid hormones that occurs after surgical treatment or during radioactive iodine treatment for hyperthyroidism/thyroid cancer
• Adverse effects: may cause liver and bone marrow toxicity
• Interactions: increased activity with oral coagulants and Increased leukopenia with other bone marrow depressants