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Pharmacology 2 > Thyroid Drugs > Flashcards

Thyroid Drugs Flashcards

1
Q

What is T4?

A

Thyroxine

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2
Q

Where is T4 made?

A

100% in the thyroid

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3
Q

Where is T3 made?

A

20% in the thyroid, the rest is from T4

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4
Q

What percentage of T3 and T4 is “free”?

A

~1%

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5
Q

Which Thyroid hormone is the “biologically active” form?

A

T3

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6
Q

Where is T4 deiodinated to T3? (3 things)

A

Liver
Kidney
Muscles

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7
Q

Which thyroid hormone enters cells more quickly?

A

T3

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8
Q

Which thyroid hormone has the more rapid onset?

A

T3

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9
Q

Which thyroid hormone is more potent?

A

T3 is 3-5x more potent than T4

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10
Q

How do thyroid hormones work?

A

They bind to receptors in the nuclei and influence production of regulatory enzymes.

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11
Q

What usually causes hypothyroidism? (2 things)

A

Lymphocytic thyroiditis

Idiopathic atrophy

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12
Q

What is the goal of treating hypothyroidism?

A

Replacing the hormone

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13
Q

What are the two pharmacologic agents available for treating hypothyroidism?

A

Levothyroxine (T4)

Liothyronine (T3)

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14
Q

Which has faster onset of action, Liothyronine (T3) or Levothyroxine (T4)?

A

Liothyronine (T3)

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15
Q

Which has a shorter half-life, Liothyronine (T3) or Levothyroxine (T4)?

A

Liothyroxine (T3)

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16
Q

Which would you use in dogs with reduced ability to convert T4 to T3?

A

T3

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17
Q

Which has greater GI absorption in dogs between T3 and T4?

A

T3

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18
Q

Which is the treatment of choice in all species with hypothyroidism and why?

A

T4, because it allows for cellular autoregulation providing T3 as the cell needs it. The longer half-life also makes dosing easier.

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19
Q

What can T3 be used to diagnose in cats?

A

Hyperthyroidism

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20
Q

How is levothyroxine usually given?

A

Oral tablet

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21
Q

When does levothyroxine reach peak plasma concentration?

A

4-12 hours

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22
Q

What is the half-life of levothyroxine?

A

12-16 hours

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23
Q

What is a caution with levothyroxine?

A

Acute overdose less of an issue than chronic

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24
Q

What can you see with thyrotoxicosis? (6 things)

A 
V&D
Tachycardia
Tachypnea
Weight loss
Hyperactivity
Hypertension
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25
How do you monitor thyroid levels?
Plasma T4
26
How often do you monitor patient thyroid levels?
4 weeks after starting dosing
27
What is the starting dose for Levothyroxine?
0.02mg/kg PO BID
28
What is the alternate dosing for dogs >50-60lbs (~25kg)?
Body surface area (0.5mg/m^2)
29
How long after stopping the drug can you see effects of Levothyroxine continue?
Up to 4 weeks
30
What is a rare manifestation of hypothyroidism?
Myxedema coma
31
In cases of Myxedema coma, what are 4 things that you do to treat?
INJECTABLE levothyroxine Warm the patient Respiratory support Fluid/electrolyte support
32
What two anticonvulsants don't interfere with thyroid testing?
Levetiracetam | Potassium bromide
33
How long can general anesthetics interfere with thyroid testing?
Up to 48 hours
34
What can hyperthyroidism cause?
Thyrotoxicosis from excess thyroid hormone (T3 and T4)
35
What is hyperthyroidism most commonly due to in cats?
Functional adenomatous hyperplasia
36
What are two less common causes of hyperthyroidism in cats?
Thyroid adenoma | Thyroid carcinoma
37
What is the cause of hyperthyroidism in dogs? (2 things)
Iatrogenic | Functional neoplasia
38
What are the 3 main treatment options for hyperthyroidism?
Radioactive iodine (I131) Antithyroid drugs Diet (Y/D)
39
What are two other treatments for hyperthyroidism?
Thyroidectomy | Intrathyroid injection of ethanol (don't recommend lots of complications)
40
What does the radioactive iodine treatment entail?
Single injection of I 131 to selectively destroy thyroid tissue
41
How long is the half-life of I 131?
~8 days
42
How long must the I 131 patient be in isolation after treatment?
1-4 weeks
43
T/F: Radioactive I 131 is very safe.
True, but it's very expensive.
44
What 3 drugs fall under Thioureylenes?
Methimazole Carbimazole Propylthiouracil (PTU)
45
How do thioureylenes work?
They inhibit synthesis of thyroid hormones by stopping organification and coupling
46
T/F: Methimazole lowers T4, but T3 is normal.
True, due to the autoregulatory mechanisms in tissues.
47
What species is Methimazole licensed for use in?
Felines
48
How do you monitor Methimazole dosing?
By checking T4 levels after 2-4 weeks
49
What are the two major side effects of Methimazole?
Vomiting, anorexia (~10%) | Transient, mild hematology changes (~15%)
50
If a cat has an idiosyncratic reaction to Methimazole, can you give it another thioureylenes?
NO! Must give the cat something from another group.
51
T/F: Transdermal methimazole prevents adverse effects?
False, it may reduce GI upset, but does not prevent other adverse effects or idiosyncratic reactions.
52
How does Carbimazole work?
It's converted to Methimazole, and then goes from there.
53
What are the three types of iodides?
Lugol's solution Potassium iodide Sodium iodide
54
How do iodides work to treat hyperthyroidism?
Inhibit organification and preformed hormone secretion
55
Are iodides considered a first line drug?
No
56
What are the two iodinated radiographic contrast agents?
Ipodate | Iopanoic acid
57
How do iodinated radiographic contrast agents help treat hyperthyroidism?
Inhibit conversion of T4 to T3 in tissues
58
What do you have to monitor with iodinated radiographic contrast agents treatment?
Monitor T3
59
Are iodinated radiographic contrast agents considered a first line drug?
No, effect questionable and may be transient.
60
How does Y/D work?
Restricted iodine reduced T3/T4
61
How do you monitor Y/D?
Monitor T4
62
T/F: Hill's Y/D has been shown to cause hypothyroidism.
False
63
What 3 things must you consider when deciding how to treat?
Treat the patient, not the disease Do no harm (weigh the risks) Client concerns (administration, cost, availability)

Pharmacology 2 (9 decks)

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