thyroid drugs ic11 + ic15 Flashcards
Causes of Hyperthyroidism (3 points)
1) Grave’s disease
TSH receptor antibodies (TRAb) mimicking TSH binding, stimulate TH production
2) Subacute thyroiditis
Release of stored thyroid hormone
Cause Hyper, then Hypo
3) Adenomas, nodules
Treatment for Hyperthyroidism (3 points, surgery, list drugs)
1) Surgical resection, Thyroidectomy
2) Radioactive iodine ablative therapy
Destroy overactive thyroid cells
CANNOT give in pregnancy
3) Antithyroid drugs
Thionamides (Carbimazole and Propylthiouracil)
Iodides
Non-selective beta blockers
Patients suitable for antithyroid drugs
1) Waiting for ablative therapy or surgical resection (except KI, do ablation first then KI)
Minimise risk of post-ablation hyperthyroidism
Depletes stored hormone
2) Mild disease, small goiter
3) Women, elderly
Examples of drugs that can block TPO
Class: Thionamides
Propylthiouracil
Carbimazole
What do patients with hepatotoxicity take?
Carbimazole
DO NOT take PTU
Why can Carbimazole be taken OD?
Concentrated in thyroid → Effect lasts whole day
Counselling point for Carbimazole / PTU
Clinical response may take 3-6 weeks
Existing T4 still persists in body, has long half life
Need to wait for present molecules to be degraded
Example of NSBB used in Hyperthyroidism
Why can NSBB be used in Hyperthyroidism?
Propranolol
Used for symptomatic relief!
Reduces adrenergic symptoms
Blocks T4 to T3 conversion at high dose
What can Propranolol be used together with?
Why?
Thionamides eg. PTU, Carbimazole
Propranolol used for short term symptomatic relief of hyperthyroidism symptoms
Thionamides take very long (3-6 weeks) to reduce T3 T4 levels, so Propranolol is taken in the meantime
Which drugs can block T4 to T3 peripheral conversion?
PTU and Propranolol
can block at high doses
Indication of NSBB (3 points)
Short term symptomatic relief
Used with Thionamide, before ablation, surgery
Treatment for thyroiditis
MOA of Iodides
example of iodide
Inhibit release of stored T3T4
Has minimal effect on TH synthesis
Limited efficacy after 14 days
Potassium iodide
Indication of iodides
Before surgery to shrink gland
After ablative therapy, inhibit thyroiditis-mediated release of stored TH
Thyroid storm
Can use KI before ablative radioactive iodine therapy?
No, do not use before ablative radioactive iodine therapy
Radioactive Iodine first -> then Potassium Iodide
May reduce uptake of radioactive iodine
Which drugs to use during hyperthyroidism in pregnancy?
1st trimester: Use PTU
Carbimazole has higher risk of congenital malformations
2nd, 3rd trimester: Use Carbimazole
PTU has higher risk of hepatotoxicity
Causes of Hypothyroidism
Primary
1) Iodine deficiency
2) Hashimoto disease
Increased AtgA and TPO antibodies which attack thyroid
3) Thyroid resection
Secondary
1) Hypothalamus (TRH) or Pituitary dysfunction (TSH)
2) Drug induced eg. amiodarone, lithium
Lab signs of Primary and Secondary Hypothyroidism (eg. TSH, T4, antibody levels)
Primary hypo
High TSH, Low T4
Positive antibodies (TPO, ATgA)
Secondary hypo
Low TSH, low T4
What is levothyroxine?
Synthetic T4
Dose of Levothyroxine (Healthy adults, 50-60yo without or with CVD)
Divide by 2 each time
Young, healthy adults: 100mcg
50-60yo with no cardiac issues: 50mcg
With CVD: 12.5 - 25 mcg
When should Levothyroxine be taken?
Take on empty stomach
30 - 60 mins before breakfast
4 hours after dinner
Take 2 hours from calcium or iron supplements
What is the target TSH level to reach during Levothyroxine therapy?
0.4 - 4
Titrate Levothyroxine dose based on symptoms, TSH level
What is Myxoedema coma?
Severe progression of Hypothyroidism
Reduced blood flow to GI, affect gut absorption of oral levothyroxine
Use IV Liothyronine (T3) or Levothyroxine
What is Liothyronine?
Synthetic T3
Has faster onset than Levothyroxine
Why does Hypothyroidism happen in Pregnancy?
What should be done to Levothyroxine dose?
Increased TBG which binds to T3 and T4
Need to increase Levothyroxine dose by 30-50% in pregnancy
What is the target TSH levels during pregnancy? (during each trimester)
Should be low
1st trimester < 2.5
2nd trimester < 3
3rd trimester < 3.5
When should subclinical Hypothyroidism be treated? (at what TSH level)
TSH > 10mIU/L
OR
TSH between 4 - 10
+ symptoms of hypothyroidism, TPO antibodies present
History of CVD, HF
What is the Negative feedback loop in Thyroid production?
- Hypothalamus detect low circulating TH, releasing Thyrotropin Releasing Hormone (TRH)
- TRH instructs anterior pituitary to release Thyroid Stimulating Hormone (TSH)
- TSH travels to Thyroid gland, gland produces Thyroid hormones (TH)
- Hypothalamus sense increased TH and stops releasing TRH
TSH levels in primary hypo VS hyper
High TSH in primary hypo
Issue: Thyroid gland not working, does not produce T3, T4
Low T3 and T4 will cause Hypothalamus to increase TRH, which increases TSH by anterior pituitary
Low TSH in primary hyper
Issue: Thyroid gland producing too much T3, T4
Hypothalamus sense high TH, decrease TRH secretion which decreases TSH production in anterior pituitary
Between T3 and T4,
Which is produced more?
Which is more potent
Which has longer half life?
T4 produced 4 times more than T3
T3 more potent
T4 has half-life of 6-7 days
T3 has half life of 2 days
What is TBG?
When is TBG elevated?
TBG = Thyroxine Binding Globulin
Elevated in pregnancy or females on estrogen contraceptive
Who requires routine screening for thyroid antibodies?
Pediatric patients, pregnant women
What monitoring should be done during Hyper and Hypothyroidism treatment?
Hyper:
Use T3, better than T4 early in therapy + TSH will be suppressed during treatment
Hypo:
Use TSH
(unless central hypo, then TSH will be low) use T4
