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Questions and Answers
For a patient weighing 102 kg with a TSH of 21.3 U/mL, what would be the calculated initial dose using the equation 107 + 0.69(TSH)?
If a patient has a BMI above 25 and experiences significant symptoms, what determination is made in regard to their dosing regimen?
Given the patient weighing 102 kg, what is the formula for calculating the dose of desiccated thyroid based on levothyroxine?
If a follow-up patient continues to exhibit unchanged TSH levels 6 weeks after starting levothyroxine, which action is primarily indicated if they are also taking an iron supplement?
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What is the most common cause of hypothyroidism in North America?
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What is the average adult replacement dosage of levothyroxine for treating hypothyroidism?
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How long should a clinician wait after a dosing adjustment before assessing TSH values?
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What could be a potential effect of overtreatment with levothyroxine?
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Which of the following drugs may interfere with the absorption of levothyroxine?
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What is a suggested initial dose of levothyroxine for patients who have negligible thyroid function?
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In what scenario should a lower starting dose of levothyroxine (12.5 – 25 mcg/day) be considered?
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What is a key difference between levothyroxine and desiccated thyroid?
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What is the primary pharmacological action of methimazole?
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Which of the following accurately describes the risks associated with radioactive iodine therapy?
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What distinguishes propylthiouracil from methimazole in terms of mechanism of action?
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Which adverse effect is specific to propylthiouracil and not methimazole?
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In which patient scenario is propylthiouracil the preferred antithyroid agent?
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Which medication is considered to have the lowest hepatotoxicity risk and is often preferred for most patients?
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What is the main therapeutic goal when treating hypothyroidism?
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Which condition is characterized by excessive thyroid hormone effects rather than production?
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Propranolol is primarily used in hyperthyroid patients for what purpose?
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What potential adverse effect is associated with antithyroid medications like methimazole and propylthiouracil?
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Study Notes
Thyroid Disorders
- Thyrotoxicosis is any condition of excessive thyroid hormone and its effects.
- Hyperthyroidism is specifically due to excess thyroid hormone production.
- Thyroid storm is a life-threatening medical emergency due to severe thyrotoxicosis.
- Graves disease, toxic nodules, iodine excess, and TSH-producing pituitary adenomas are causes of hyperthyroidism.
- Surgery is an option for patients with hyperthyroidism.
- Hypothyroidism is a possible consequence of thyroid surgery.
Treatment for Hyperthyroidism
- Radioactive iodine (I131) is used to ablate thyroid tissue in patients with Graves disease and toxic nodules.
- Methimazole, propylthiouracil are antithyroid agents that interfere with the production of thyroid hormone.
- Methimazole is generally preferred over propylthiouracil due to lower risk of hepatoxicity.
- Propranolol is a beta-blocker used to manage symptoms of hyperthyroidism.
Treatment for Hypothyroidism
- Levothyroxine, a synthetic T4 hormone, is the standard therapy for hypothyroidism.
- Desiccated thyroid contains both T4 and T3 in fixed amounts and can be used based on patient preference.
Levothyroxine
- Average adult replacement dose: 1.6 mcg/kg/day.
- Initial doses vary depending on endogenous thyroid function and can range from 25–50 mcg to full replacement dosages.
- Dose adjustments should be made after 6 weeks.
- Interactions: Antacids, mineral supplements, proton pump inhibitors, estrogens can interfere with absorption.
- Adverse effects: Symptoms of hyperthyroidism if overtreated, exacerbation of angina, potential for decline in glycemic control.
Desiccated Thyroid
- Dose recommendations: 32–325 mg depending on the equivalent levothyroxine dose (50–500 mcg).
- Adverse effects: Similar to levothyroxine, but with higher risk of cardiovascular or neurological adverse effects at higher doses due to the presence of T3.
Prescribing Levothyroxine
- Consider patient history and thyroid function: Age, BMI, presence of cardiovascular disease, level of TSH, and presence of an intact thyroid.
- Initial dose: Conservative initial dosing is 25-50 mcg for patients with an intact thyroid and mild symptoms.
- Follow-up and dose adjustments: Monitor TSH levels and adjust dose accordingly after 6 weeks.
Example Case #1
- Patient: 48-year-old female with mild symptoms and mildly elevated TSH, BMI under 25, intact thyroid.
- Initial dose: 25–50 mcg levothyroxine.
Example Case #2
- Patient: 56-year-old female with significant symptoms, fairly high TSH, BMI above 25, intact thyroid.
- Initial dose: 1.6 x weight in kg (163.2 mcg), 1.6 x ideal body weight (94 mcg), or 107 + 0.69(TSH) (121 mcg).
Sample Question
- Answer: D. Change the time the patient takes their iron supplement.
- Iron supplements can interfere with levothyroxine absorption. Separating administration by a few hours can improve absorption.
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Description
This quiz covers key concepts related to thyroid disorders such as thyrotoxicosis, hyperthyroidism, and treatment options including medications and surgery. Understand the causes, symptoms, and management of these conditions, and learn about the interventions like radioactive iodine therapy and antithyroid agents.
