Thyroid

Question 1

Indication iodine?

Answer 1

(Potassium iodide)

Treat simple non-toxic goitre iodine deficiency

Question 2

Indication iodized salt?

Answer 2

Prevent endemic goitre

Question 3

Indication levothyroxine?

Answer 3

Uncomplicated hypothyroidism maintenance treatment first line

Question 4

Liothyrinone indication? (2)

Answer 4

L-triiodothyronine sodium
Severe hypothyroidism where rapid effect needed, (shorter half life 1 day)
myxoedema coma :crush tablets and give via NGT.

Question 5

Levothyroxine moa? (5)

Answer 5

• T4 (thyroxine prohormone), which is converted to t3 in Vivo to replace endogenous hormone.
• t3 bind to thyroid nuclear receptor which increase transcription of genes involved in following functions:
- stimulate metabolism
-Promote normal growth and maturation
- sensitise to effect of catecholamines.

Question 6

Dose levothyroxine?

Answer 6

Start with 50 mcg single dose and increase at 2-3 week intervals by 20-50 until clinically respond.
Nb start with lower dose (25) in elderly and those with cv disease because very sensitive to t4.
Take on empty stomach!

Question 7

Name an nb pharmacokinetic property of levothyroxine

Answer 7

• > 99% plasma protein bound (drug interactions)
• peak therapeutic effect 3-4 weeks
• half life 6-7 days

Question 8

Name 5 drug interactions with levothyroxine

Answer 8

• Caco3 and fe so4: decreased absorption
• colestyramine: bind t4 in git
• oestrogen: increased sTBG
• warfarin: potentiate anticoagulant
• antidiabetic agents and insulin

Question 9

Name 5 adverse effects levothyroxine

Answer 9

(Increased metabolism)
• chronic: osteoporosis!
• arrhythmia!, tachycardia, angina
• skeletal muscle cramps
• weight loss
• restlessness, insomnia, excitability
• sweating and flushing

Question 10

Liothyridine moa? (3)

Answer 10

T3. Bind to thyroid nuclear r causing transcription genes for following functions:
• stimulate metabolism
• promote normal growth and maturation
• sensitise to effects catecholamines.

Question 11

Name 2 antithyroid classes and examples

Answer 11

• Thiouracils: propylthiouracil (not in sa)

* Sulfur containing imidazole derivatives: carbimazole

Question 12

Indication carbimazole?

Answer 12

• Treat hyperthyroidism
• prepare patients for surgical resection or irradiation
• long term treatment graves disease

Question 13

Moa carbimazole?

Answer 13

Interfere with thyroxin synthesis in thyroid
• converted to active metabolite methimazole
• inhibit thyroid peroxidase.
• divert oxidised iodine away from thyroglobulin therefore decrease synthesis
• concentrated in cells with peroxidase system: salivary glands, neutrophils, macrophages, monocytes, thyroid follicular cells

Question 14

Dose carbimazole

Answer 14

Initially 20-60 mg daily until euthyroid

Then reduced to maintenance 5-15.

Question 15

Name 2 drug interactions with carbimazole

Answer 15

Enhance anticoagulation effect:
• oral anticoagulants
• heparin

Question 16

Name 5 adverse effects carbimazole.

Answer 16

• Allergic rashes and pruritis common.
• hepatotoxic: cholistatic hepatitis
• agranulocytosis
• git
• headache
• alopecia

Question 17

Treatment thyroid crisis? (4)

Answer 17

1. Carbimazole
2. iodine (inhibit release preformed t3 and t4)
3. Propanalol or other B blockers ( only if good lv fx ) ( rx symptoms tachycardia)
4. Glucocorticoids eg hydrocortisone iv (reduce mortality)