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MHD2/Pharm - Endocrine > Pharm - Thyroid/Antithyroid > Flashcards

Pharm - Thyroid/Antithyroid Flashcards

1
Q

Cardiovascular function of thyroid hormone

A

Increased CO

Decreased vascular resistance

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2
Q

Metabolic function of thyroid hormone

A

Increase BMR, heat production, O2 consumption, and LDL receptor expression

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3
Q

Respiratory function of thyroid hormone

A

Increase respiratory rate

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4
Q

Bone/Skin function of thyroid hormone

A

Bone growth
Epidermis and dermis
Hair and nails
Sweat glands

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5
Q

CNS function of thyroid hormone

A

CNS development and responsiveness

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6
Q

Growth function of thyroid hormone

A

Promotes growth

Required for fetal development

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7
Q

Skeletal muscle function of thyroid hormone

A

Required for muscle function

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8
Q

Describe the regulation of thyroid hormone synthesis

A

The HPT axis controls thyroid hormone synthesis.
TSH from the anterior pituitary stimulates thyroid hormone production. Iodine and thyroglobulin combine to make MIT and DIT (organificaiton) and then are coupled within the colloid to form T3 and T4. Both steps are catalyzed by TPO.

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9
Q

How are thyroid hormones transported in the blood?

A

Bound to thyroxine-binding globulin (T3 and T4) and transthyretin (T4 only)
Only the unbound hormone is active

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10
Q

What effect does pregnancy have on thyroid hormone transport?

A

Increased estrogen associated with pregnancy increases the TBG levels, thus decreasing the amount of free T4, decreasing the biological activity

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11
Q

How is T4 converted to T3?

A

Deiodinase enzymes: Type 1 activates T4 to T3 in the liver and kidney. Type 2 activates T4 to T3 intracellularly in target tissues.

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12
Q

What are the two major disorders of the thyroid gland?

A

Hypothyroidism: Hashimotos thyroiditis
Hyperthyroidism: Grave’s disease

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13
Q

Diagnose a patient with Low T4/T3 and high TSH

A

Hypothyroidism: most likely Hashimotos thyroiditis

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14
Q

Diagnose a patient with High T4/T3 and low TSH

A

Hyperthyroidism: Could be pituitary adenoma, Grave’s disease

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15
Q

What are the treatment options for hypothyroidism

A

Levothyroxine: synthetic T4 (Drug of choice)
Liothyronine: synthetic T3

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16
Q

What is a major pharmacokinetic difference between Levothyroxine and Liothyronine?

A

Levothyroxine has a slow onset whereas Liothyronine is rapid onset. This allows levothyroxine to be taken once daily, unlike liothyronine which requires multiple doses per day.

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17
Q

When would you use liothyronine instead of levothyroxine?

A

In cases when rapid action is required such as myxedema coma or preparing a patient for radioiodine therapy

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18
Q

Once T4 therapy is begun, how long does it take for improvement?

A

Improvements should begin in about 2 weeks
TSH levels reach steady state in about 6 weeks
Full recovery can take months

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19
Q

How is T4 therapy monitored?

A

TSH levels are checked to assess therapeutic efficacy

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20
Q

What risks are associated with over replacement of T4?

A

Hyperthyroidism
Risk of atrial fibrillation
Increased bone loss in post-menopausal women

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21
Q

What are the major types of drug interaction with levothyroxine?

A

Inhibitors of absorption: Ca/Fe supplements, fiber, cholestyramine, ciprofloxacin, antacids
Increased metabolism: Rifampin, carbamazepine, phenytoin, phenobarbital, St. John’s wort
Increased TBG: pregnancy, cirrhosis, estrogen therapy

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22
Q

How is hypothyroidism treated in pregnant patients?

A

TSH receptors in pregnant patients do not respond to beta-hCG agonism like normal patients. They require increased dose of levothyroxine, regular TSH monitoring to support fetal development

23
Q

What is myxedema coma?

A

Severe hypothyroidism can cause impaired mental status, hypothermia, hypotension, bradycardia, hypoglycemia and hypoventilation.
Usually triggered by acute event
30-40% mortality

24
Q

What is the treatment for myxedema coma?

A

IV levothyroxine and/or liothyronine
Mechanical ventilation
Electrolytes
Correction of hypothermia

25
Q

What are the therapies used to treat hyperthyroidism?

A 
Beta blockers (symptomatic relief)
Antithyroid drugs
Iodide
Radioactive iodine therapy
Surgery
26
Q

How does propranolol help with hyperthyroidism?

A

Prevents palpitations, tremor, anxiety and heat intolerance associated with increased adrenergic response of hyperthyroidism

27
Q

What are the contraindications for beta blockers?

A

Asthma, COPD, heart failure

28
Q

What are the two antithyroid drugs?

A

Propylthiouracil (PTU)

Methimazole (MMI)

29
Q

What is the mechanism of action of PTU and MMI?

A

They inhibit synthesis of thyroid hormones by inhibiting TPO (affects organification and coupling steps)

30
Q

What is the onset time for PTU and MMI?

A

3-4 weeks because these drugs do not affect the pre-existing stored T3/T4. Once stores are depleted, PTU and MMI begin to show effect.

31
Q

What is one major difference between action of PTU and MMI?

A

PTU partially inhibits peripheral conversion of T4 to T3, MMI does not

32
Q

Therapeutic use of PTU and MMI

A

Hyperthyroidism in Grave’s disease
Adjunt to radioiodide therapy to improve recovery
Control hyperthyroidism leading up to surgery

33
Q

What adverse effects are associated with PTU and MMI?

A

Pruritus, rash, uticaria (treated with antihistamines)
Joint pain
Fever

Rare:
PTU is associated with hepatotoxicity, ANCA-positive vasculitis, agranulocytosis
MMI is associated with teratogenicity and agranulocytosis

34
Q

When is MMI indicated and when is PTU indicated?

A

MMI preferred for non-pregnant patients

PTU is preferred for pregnant patients during the first trimester (then switch to MMI)

35
Q

What are the two preparations of iodide treatment?

A

Saturated potassium iodide (SSKI)

Potasium iodide-iodine (Lugol’s solution)

36
Q

What effects does high dose iodide have?

A

Inhibits thyroid hormone synthesis
Acute inhibition of homrone secretion (Thyroid storm)
Decreases vascularity of thyroid gland

37
Q

What is the Wolff-Chaikoff effect?

A

Iodide acts in negative feedback to inhibit organification by TPO. This is useful for treating people involved with nuclear disasters to prevent radioiodine uptake

38
Q

What are the indications for iodide treatment?

A

Severe hyperthyroidism/ Thyroid storm
Adjunctive therapy with radioactive iodine
Adjunctive therapy with antithyroid drugs in Graves disease
Preoperative for thyroidectomy

39
Q

What are the indications of radioactive iodine treatment?

A

Treatment of choice for Graves disease and toxic nodular goiter

40
Q

What is the mechanism of action of radioactive iodine?

A

Concentrated in the thyroid gland
Emits beta particles which act directly on parenchymal cells leading to follicular cell necrosis, ablation of the thyroid.

41
Q

How does radioactive iodine treatment differ for elderly patients, coronary artery disease, or those intolerant of hyperthyroid symptoms

A

Must be pretreated with antithyroid (MMI) for 4-6 weeks to establish euthyroid state

42
Q

What are the adverse effects of radioactive iodine treatment?

A

Radiation thyroiditis

Exacerbation of Graves ophthalmopathy

43
Q

What are the contraindications of radioactive iodine treatment?

A

Pregnancy

Severe opthalmopathy

44
Q

What are the indications for thyroid surgery?

A

Patients with large goiters cause airway obstruction
Patients who refuse radioiodine therapy and antithyroid drugs
Patients with severe opthalmopathy
Patients resistant to other therapies

45
Q

What are patients undergoing thyroidectomy at risk of developing?

A

Thyroid storm

Prevented by pre-treating with antithyroid drugs

46
Q

Which hyperthyroid treatment is most effective? Thionamides, radioiodine, surgery

A

All are equally effective

47
Q

What is thyroid storm?

A

A rare, life-threatening condition (10-30% mortality)

Exaggeration of hyperthyroid symptoms: tachycardia, hyperpyrexia, agitation, delirium, psychosis

48
Q

What is the treatment for thyroid storm?

A 
Propranolol
PTU
Iodide
Dexamethasone (blocks peripheral conversion of T4 to T3)
Cholestyramine (block reabsorption)
49
Q

What is a common drug that can induce thyroid disease?

A

Amiodarone

50
Q

How does amiodarone cause thyroid disease?

A

It contains iodine that is released during metabolism. This causes Wolff-Chaikoff effect leading to destructive thyroiditis

51
Q

How is amiodarone induced hypothyroidism treated?

A

T4 supplementation

52
Q

How is amiodarone induced hyperthyroidism treated?

A

Anti-thyroid drugs, radioiodine, surgery are used to treat in cases of pre-existing multinodular goiter or Graves

Glucocorticoids are used to treat inflammation if the toxic effect is due to destructive thyroiditis, release of preformed T4/T3

53
Q

What is the treatment strategy for thyroid carcinoma?

A

Total thyroidectomy followed by radioiodine ablation to destroy any residual carcinoma and metastases

54
Q

How is iodine uptake stimulated before radioiodine ablation therapy?

A

Withdraw levothyroxine for 4-6 weeks
Levothyroxine withdrawal with liothyronine administration
IV injection of rTSH

MHD2/Pharm - Endocrine (7 decks)

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