Pharmacology

1. Hypo & Hyperthyroidism
Dr. Salman
Pharmacology

2. Hypothyroidism etiology
• Something about the gland itself
• Primary (95%)
– Chronic thyroiditis (Hashimoto’s)
– Post-ablative surgery (RAI)
– Drugs (lithium)
– Heritable biosynthetic defects
– Iodine deficiency
• Suprathyroid causes are rare

3. Hypothyroidism
• It is treated with the hormone itself!
– Thyroxine, or 3,5,3',5'-tetraiodothyronine
(often abbreviated as T4)
– Injected T4

4. Myxedema Coma
• High doses of T4, T3
• Corticosteroid
• Warming blankets
• IV fluids

5. Antihyperthyroid Drugs

6. The synthesis of thyroid hormone
and action and effects of
antithyroid agents

7. Thyroid hormone
synthesis and action
Effects of antithyroid
agents
1 Active accumulation of
iodide into the gland
Basis for selective cell
destruction of 131I
2 Oxidation of iodide by
peroxidases
Inhibited by thioamides
3 Iodination of tyrosyl
residues on thyroglobulin
from MIT and DIT
Inhibited by thioamides
4 Coupling of MIT and DIT
to form T3 and T4
Inhibited by thioamides
5 Proteolytic release of T3
and T4 from thyroglobulin
Inhibited by high doses of
iodide
6 Conversion of T4 to T3 via
5’ deiodinase in
peripheral tissues
Inhibited by propranolol,
and propylthioiracil

9. Thioamides: Propylthiouracil and Methimazole
• Use in uncomplicated hyperthyroid conditions;
• High-dose propylthiouracil inhibits 5' deiodinase
• Common maculopapular rash
• Less common  prothrombin, hypersensitivity,
and immune-based arthralgia,
• jaundice, lupus, and vasculitis
• Both drugs cross the placental barrier, but PTU
is safer in pregnancy because it is extensively
protein bound

10. Common Causes of
hyperthyroidism
• Graves disease
• Toxic multinodular goiter
• Subacute thyroiditis
• Extrathyroid source
– Thyrotoxicosis factitia
– Struma ovarii
• Excess TSH (rare)

11. Treatment Graves disease
• Immediate treatment
– Propranolol
– Antithyroid drugs
• PTU
• Methimazole
• Long-term treatment
– RAI ablation
– Thyroidectomy

12. Rx Toxic multinodular goiter
• Radioactive Iodine

13. Rx Thyroid Storm
• Antithyroid drugs
• Iodine
• Beta-blockers
• Dexamethasone
• IV fluids, cooling blankets

14. Iodide
• KI+ iodine (Lugol's solution) possible use in
thyrotoxicosis: used preoperatively, →↓
gland size, fragility, and vascularity
• No long-term use because thyroid gland
"escapes" from effects after 10-14 days