150 Questions
What is the recommended time window for administering levothyroxine in relation to meals?
60 minutes before meals or 4 hours after meals
Why should levothyroxine dosage changes be made slowly?
To avoid transient serum alterations
What is the half-life of levothyroxine?
7 days
Why is liotyronine (T3) not recommended for long-term use?
It has a shorter half-life and requires multiple daily doses
What is the clinical indication for levothyroxine administration?
Hypothyroidism
What is the most appropriate initial levothyroxine replacement dose for a young patient with no cardiac disease?
1.7 mcg/kg/day
Why should levothyroxine be taken orally on an empty stomach or at bedtime?
To ensure optimal absorption
When should thyroid function tests be monitored after starting levothyroxine therapy?
After 6-8 weeks
Why might lower thyroxine doses be considered for a patient taking omeprazole?
Omeprazole interferes with levothyroxine absorption
When should levothyroxine administration be separated from calcium intake?
4 hours before calcium intake
What is the primary reason for the initial methimazole treatment being preferred over propylthiouracil?
Methimazole has a longer duration of action and can be dosed once daily
What is the rationale for preferring once daily dosing of methimazole over propylthiouracil?
Methimazole has a longer half-life
What is the recommended administration frequency for methimazole?
Every 6-8 hours
Why was methimazole preferred over propylthiouracil for initial treatment?
Methimazole has an improved safety profile
What is the role of serum FT4 and FT3 concentrations in determining the hormone's biological activity?
They exist in the free form and determine the hormone's biological activity
What is the primary mechanism by which T4 is converted to T3?
Deiodinases in peripheral tissues such as kidneys and liver convert T4 to T3
What is the preferable practice for patients using levothyroxine to avoid changes in bioavailability?
Remaining on a consistent levothyroxine preparation between refills
Which type of thyroxine is the preparation of choice for thyroid replacement and suppression therapy?
Levothyroxine (T4)
Which component is responsible for the stability and content uniformity of levothyroxine preparations?
Levothyroxine itself
What is the effect of iodide therapy on the size and vascularity of a hyperplastic thyroid gland?
It decreases the size and vascularity
When is iodide therapy clinically indicated for thyroid storm?
As a first-line treatment
Why should chronic use of iodides in pregnancy be avoided?
They may cause fetal goiter as they cross the placenta
What are the disadvantages of iodide therapy?
All of the above
What are the toxicities associated with chronic use of iodides?
Swollen salivary glands and mucous membrane ulcerations
Which antithyroid medication is preferably given in the 1st trimester of pregnancy due to its strong protein binding and reduced placental crossing?
Propylthiouracil
What is the primary pharmacodynamic action of thioamides like Methimazole and Propylthiouracil?
Inhibiting the thyroid peroxidase-catalyzed reactions
Which antithyroid medication inhibits peripheral deiodination of T4 to T3?
Propylthiouracil
What is the most dangerous adverse reaction associated with thioamides like Methimazole and Propylthiouracil?
Agranulocytosis
Why are iodides rarely used as sole therapy for hyperthyroidism today?
They are ineffective at inhibiting hormone synthesis
What effect do thioamides have on hormone synthesis?
Inhibiting hormone synthesis
What distinguishes the onset of thioamides from other antithyroid agents?
Slow onset requiring 3 - 4 weeks before T4 stores are depleted
What is the reported incidence of severe hepatitis associated with Propylthiouracil (PTU) use?
~3%
Which antithyroid medication is associated with a higher incidence of cholestatic jaundice?
Methimazole
What percentage of patients experience agranulocytosis due to thioamide treatment?
<0.1%
Which of the following is a characteristic symptom of hyperthyroidism?
Heat intolerance
Which antithyroid drug has a half-life of about 1.5 hours?
Methimazole
Which of the following drugs is an active metabolite of Carbimazole?
Methimazole
What is the primary pharmacological action of Propylthiouracil?
Inhibits peripheral deiodination of T4 to T3
What is the preferable and effective strategy for definitive treatment of hyperthyroidism before becoming pregnant?
Thyroidectomy
What is the effect of radioactive iodine (RAI) therapy on JP's thyroid function?
It caused hypothyroidism and required levothyroxine replacement therapy.
Why did JP receive calcium carbonate three times daily?
To manage the bone complications associated with her thyroid condition.
What is the significance of JP's delayed reflexes on physical examination?
Suggests hypothyroidism and reduced nerve conduction velocity.
What is the primary reason for JP's weight gain despite experiencing symptoms of hyperthyroidism previously?
The metabolic changes associated with hypothyroidism caused weight gain.
Why did JP receive omeprazole?
To counteract the gastrointestinal side effects of methimazole and propranolol.
What is the primary cause of primary hypothyroidism?
Defects in the thyroid gland
Which medication is part of the treatment protocol for differentiated thyroid cancer to prevent recurrence after total thyroidectomy?
Radioactive iodine
What is the primary mechanism of action of anti-thyroid hormones like Methimazole and Carbimazole?
Inhibiting the conversion of T4 to T3
What is the primary cause of secondary or central hypothyroidism?
Defects at the level of the pituitary gland or hypothalamus
Which type of antithyroid medication reduces thyroid activity and hormone effects by interfering with the production of thyroid hormones?
Thioamides
Which drug is indicated for the preoperative preparation of a hyperplastic thyroid gland to decrease size and vascularity?
Iodide therapy
What is the primary disadvantage of iodide therapy?
Increase in intraglandular stores of iodine
What is a potential adverse reaction associated with chronic use of iodides?
Bleeding disorders
In which clinical condition is iodide therapy contraindicated?
Fetal goiter in pregnancy
What effect does iodide therapy have on a hyperplastic thyroid gland?
Reduces size and vascularity
How is radioactive iodine administered for the treatment of thyrotoxicosis?
Orally in solution as sodium 131I
What is the effective half-life of the β rays emitted by radioactive iodine for the treatment of thyrotoxicosis?
5 days
What is a significant advantage of radioiodine therapy for hyperthyroidism?
Easy administration
Why should radioactive iodine not be administered to pregnant women or nursing mothers?
It destroys the fetal thyroid gland and is excreted in breast milk
What clinical syndrome results from tissues being exposed to high levels of thyroid hormone?
Thyrotoxicosis
What is the optimal TSH range that should be maintained for patients undergoing levothyroxine therapy?
0.5–2.5 mIU/L
What is the suggested time interval for separating levothyroxine administration from calcium intake to ensure optimal absorption?
4 hours
What may be a reason for inadequate levothyroxine replacement in a patient with an elevated TSH level?
Concurrent administration with omeprazole
What is the suggested approach to optimize levothyroxine absorption in a patient taking omeprazole?
Stopping omeprazole altogether
When should thyroid function tests be monitored after starting levothyroxine therapy?
After 6–8 weeks
What is the effect of chronic use of iodides in pregnancy?
Increased risk of hyperthyroidism in the newborn
For whom may once weekly thyroxine injections be effective?
Patients who struggle with daily medication adherence
Which antithyroid medication inhibits peripheral deiodination of T4 to T3?
Propylthiouracil
Why might lower thyroxine doses also be considered for a patient taking omeprazole?
Omeprazole impairs levothyroxine absorption
What is the primary role of TSH Releasing Hormone (TRH) in regulating thyroid hormones?
Signaling the hypothalamus to produce more or less TSH
What is the physiological consequence of low levels of T3 and T4 in the blood?
Increased release of TSH by the pituitary gland
What is the exclusive physiological role of iodine in relation to thyroid hormones?
Essential for normal synthesis of thyroid hormones
Which organ plays a critical role in regulating metabolic activities such as body temperature and menstrual cycles?
Thyroid gland
What is the primary function of THYROXINE (T4) and TRIIODOTHYRONINE (T3) in the body?
Determinants of brain and somatic development
What is the recommended time window for administering levothyroxine in relation to meals?
60 minutes before meals
Why is liotyronine (T3) not recommended for long-term use?
It requires multiple daily doses
What is the optimal TSH range that should be maintained for patients undergoing levothyroxine therapy?
0.5–2.5 mIU/L
What is the primary pharmacological action of Propylthiouracil?
Suppressing thyroid hormone production
What effect do certain foods and drugs have on the absorption of levothyroxine?
Impair its absorption
What is the primary clinical indication for thyroid storm?
Improvement in thyrotoxic symptoms
Which of the following is a disadvantage of iodide therapy?
Delay in the onset of thioamide therapy
What is the potential toxicity associated with chronic use of iodides in pregnancy?
Fetal goiter and crossing the placenta
What is the primary adverse reaction to iodine (IODISM)?
Drug fever and acneiform rash
Which clinical condition is iodide therapy contraindicated?
Thyroid storm
What is the most significant advantage of levothyroxine over liothyronine for thyroid hormone replacement therapy?
Longer duration of action
In the context of thyroid hormone replacement therapy, which factor favors the use of liothyronine over levothyroxine?
Rapid relief of symptoms
In a patient with hypothyroidism, which symptom is most likely to persist despite adequate levothyroxine replacement?
Puffy face
Which characteristic best describes the action of thioamides like carbimazole and methimazole in the treatment of hyperthyroidism?
Inhibition of thyroid hormone release
In the treatment of neonatal Grave’s disease, which mechanism supports the use of antithyroid drugs like propylthiouracil and methimazole?
Inhibition of thyroid hormone synthesis
What is the primary cause of primary hypothyroidism?
Defects in the thyroid gland itself
In the context of thyroid hormone replacement therapy, what is the primary function of Thioamides?
To reduce thyroid activity by interfering with the production of thyroid hormones
What is the clinical significance of TSH suppression in the context of differentiated thyroid cancer treatment?
It prevents recurrence after total thyroidectomy
What is the primary difference between primary hypothyroidism and secondary (central) hypothyroidism?
Primary hypothyroidism is due to defects in the thyroid gland itself, while secondary hypothyroidism is due to defects at the level of the pituitary gland or hypothalamus
What is the primary effect of Iodides in the context of anti-thyroid hormones?
To increase radioiodine uptake in the thyroid gland
What is the recommended approach to optimize levothyroxine absorption in a patient taking omeprazole?
Stop omeprazole administration
Why might lower thyroxine doses be considered for a patient taking omeprazole?
Omeprazole interferes with levothyroxine absorption
What is the primary role of liothyronine in thyroid hormone replacement therapy?
Rapid correction of hypothyroid symptoms
When should thyroid function tests be monitored after starting levothyroxine therapy?
After 6–8 weeks
Why might once weekly thyroxine injections be effective for some patients?
In case of nonadherence to daily dosing
What is the primary advantage of using synthetic levothyroxine for thyroid replacement and suppression therapy?
It provides stability, content uniformity, and easy laboratory measurement of serum levels
In the context of thyroid hormone replacement, what differentiates levothyroxine from liothyronine?
Liothyronine has a shorter half-life than levothyroxine
What is the key consideration for maintaining patients on a consistent levothyroxine preparation between refills?
To ensure consistency in bioavailability
In the context of thyroid function evaluation, which combination of hormone levels indicates hyperthyroidism?
Increased levels of FT4 and FT3, and decreased level of TSH
What is the primary role of thyroxine-binding globulin (TBG) in the transport of thyroid hormones?
To transport T4 and T3 in the bloodstream
What is the primary role of Thyroid-Stimulating Hormone (TSH) in regulating thyroid hormones?
Increasing the release of TSH when T3 and T4 levels are low
What is the exclusive physiological role of iodine in relation to thyroid hormones?
Aiding in the synthesis of thyroid hormones
What is the primary pharmacodynamic action of thioamides like Methimazole and Propylthiouracil?
Inhibiting peripheral deiodination of T4 to T3
What is the suggested approach to optimize levothyroxine absorption in a patient taking omeprazole?
Administering levothyroxine at least 4 hours apart from omeprazole
What is the role of serum FT4 and FT3 concentrations in determining the hormone's biological activity?
Evaluating the biological activity of thyroid hormones
Why is liotyronine (T3) not recommended for long-term use?
It has a short half-life and may cause fluctuations in hormone levels
How does iodide therapy affect the size and vascularity of a hyperplastic thyroid gland?
It increases the size and vascularity
Which adverse reaction is more commonly associated with methimazole compared to Propylthiouracil?
Cholestatic jaundice
What is the primary mechanism of action of Propylthiouracil in inhibiting hormone synthesis?
Inhibiting peripheral deiodination of T4 to T3
What was the major antithyroid agent prior to the introduction of thioamides in the 1940s?
Iodides
What is the most dangerous complication associated with thioamides like Propylthiouracil and Methimazole?
Agranulocytosis
What is the role of iodides in the context of anti-thyroid hormones?
Blocking organification of iodine
What is the primary pharmacological action of Propylthiouracil and Methimazole?
Inhibition of thyroglobulin proteolysis
What is the potential toxicity associated with chronic use of iodides in pregnancy?
Bleeding disorders
Why are iodides rarely used as sole therapy for hyperthyroidism today?
They cause an increase in intraglandular stores of iodine
How does radioactive iodine (RAI) therapy affect thyroid function?
It reduces the size of hyperplastic thyroid glands
What is the effect of iodide therapy on a hyperplastic thyroid gland?
Decreases the size and vascularity
Which of the following antithyroid medications has a longer duration of action allowing once daily dosing and an improved safety profile?
Methimazole
What is the primary cause of secondary or central hypothyroidism?
Deficiency in TSH or TRH production by the pituitary or hypothalamus
What is the potential toxicity associated with chronic use of iodides in pregnancy?
Fetal goiter or hypothyroidism
In the context of thyroid function, what effect does iodide therapy have on the size and vascularity of a hyperplastic thyroid gland?
Increases size and vascularity
What distinguishes the onset of thioamides like Methimazole from other antithyroid agents?
Delayed onset of action
Which medication has the primary pharmacodynamic action of inhibiting thyroid hormone synthesis by interfering with iodine oxidation and organification?
Methimazole
In the context of toxicity, which medication is associated with a rare but serious adverse effect known as agranulocytosis, a significant reduction in white blood cells?
Propylthiouracil
What is the primary reason why radioactive iodine should not be administered to pregnant women or nursing mothers?
It crosses the placenta to destroy the fetal thyroid gland
In the context of hyperthyroidism, which medication is contraindicated due to its potential to worsen the condition by causing temporary hypothyroidism followed by a surge in thyroid hormone production?
Iodides
Which medication is primarily used for the acute management of severe hyperthyroidism such as thyroid storm, due to its additional effect of inhibiting the peripheral conversion of T4 to T3?
Propylthiouracil
What is the primary mechanism of action of Thioamides like Methimazole and Carbimazole?
Inhibition of thyroid hormone production by interfering with the activity of the enzyme thyroperoxidase
What is the most significant adverse effect associated with the chronic use of Iodides for hyperthyroidism?
Agranulocytosis
What is the primary pharmacodynamic action of Propylthiouracil (PTU)?
Inhibition of peripheral deiodination of T4 to T3 in the liver
What is the effect of radioactive iodine (RAI) therapy on a hyperplastic thyroid gland?
Decreases its size and vascularity
In the context of iodide therapy, what is the most common toxicity associated with chronic use?
Iodism
What is the primary advantage of methimazole over propylthiouracil in the treatment of hyperthyroidism?
Methimazole has a stronger inhibitory effect on T4 to T3 conversion than propylthiouracil
In the context of iodide therapy for hyperthyroidism, what is the most significant disadvantage of using iodides?
Iodides can worsen the vascularity of a hyperplastic thyroid gland
Why is iodide therapy contraindicated in patients with multinodular goiter?
Iodides can worsen the vascularity of a hyperplastic thyroid gland
What is the primary pharmacological action of radioactive iodine in the treatment of hyperthyroidism?
Selective destruction of thyroid tissue
Why is methimazole preferred over propylthiouracil for initial treatment in pregnant patients with hyperthyroidism?
Methimazole has a lower risk of crossing the placenta than propylthiouracil
What is the primary pharmacological action of Propylthiouracil?
Inhibits the synthesis of thyroid hormones
What is the potential toxicity associated with chronic use of iodides in pregnancy?
Fetal goiter
What is the primary cause of primary hypothyroidism?
Inflammatory destruction of the thyroid gland
What is the primary effect of Iodides in the context of anti-thyroid hormones?
Reduces thyroid hormone synthesis
When is iodide therapy clinically indicated for thyroid storm?
In severe cases of thyrotoxicosis with organ dysfunction
What is the reported incidence of severe hepatitis associated with Propylthiouracil (PTU) use?
1 in 1,000,000
What is the potential adverse reaction associated with chronic use of iodides?
Nephrotoxicity
What is the primary role of Thyroid-Stimulating Hormone (TSH) in regulating thyroid hormones?
Stimulating the synthesis and secretion of T3 and T4
What is the exclusive physiological role of iodine in relation to thyroid hormones?
Is essential for hormone synthesis
What is the primary difference between primary hypothyroidism and secondary (central) hypothyroidism?
Primary - Increased TSH; Secondary - Decreased TSH
Test your knowledge on the transport and function of thyroid hormones, including the role of thyroxine-binding globulin (TBG), transthyretin, albumin, and lipoproteins. Explore topics such as the conversion of T4 to T3 by deiodinases in peripheral tissues and the evaluation of thyroid function.
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