Thyroxine and anti-thyroid medicines Pharmacology
Thyroxine and anti-thyroid medicines
1.Recapitulate the basic physiology of synthesis, storage and release of thyroxine.
2. Identify the common presentations of thyroid disorders.
3. Describe the pharmacological principles of management of thyroid disorders.
4. Classify medicines used in the management of hyperthyroid states giving examples.
5. Explain pharmacodynamics, pharmacokinetics, dosage forms and routes, indications, therapeutic efficacy, adverse
effects, cautions, contraindications, interactions with medicines, cost and availability of medicines used in thyroid
disorders including; • hypothyroidism • hyperthyroidism
6. Critically appraise the differences between the different treatment modalities used in the management of
hyperthyroid states.
7. Describe the principles of management of thyroid emergencies.
8. Discuss the safe use of thyroxine and anti-thyroid medicines in special populations including pregnancy.
9. Advice patients who are prescribed medicines for thyroid disorders.
Synthesis, storage and release of thyroxine
Main steps
1) uptake of plasma iodide by the follicle cells
2) oxidation of iodide
3) iodination of tyrosine residues of thyroglobulin
4) secretion of thyroid hormone
Piyumal Fernando 1
, Thyroxine and anti-thyroid medicines Pharmacology
Medicines in hypothyroidism
𝐓𝐓𝟑𝟑 𝐓𝐓𝟒𝟒
Biological Activity More potent (about 4 times as T4) Less potent
Binding to plasma Weak Strong (15 times more tightly bound)
protein
Half-life 1-2 days in euthyroids 7 days in euthyroids
Onset of action Quick (maximum effects within 24 Slow (10 days for maximum effects)
hours)
Duration of action Short (1 week) Long (2 – 3 weeks)
• Not used routinely. • Routinely used for
Clinical Indications • Used in Emergency replacement therapy.
indications. Eg: Hypothyroid
Coma.
Indications
1. Hypothyroidism (Replacement therapy)
a. Congenital hypothyroidism
b. Acquired hypothyroidism (Myxoedema)
2. TSH suppression therapy for non toxic goitre (Pharmacotherapy)
3. After thyroidectomy for thyroid malignancy (Replacement therapy)
• Levothyroxine should not be used to treat obesity or as a hypo-cholesterolemic agent.
Preparations
LEVOTHYROXINE SODIUM (𝐓𝐓𝐓𝐓)
Available as tablets (100 µg, 50 µg, 25 µg) and injections.
𝐓𝐓𝐓𝐓 is preferred over 𝐓𝐓𝐓𝐓 because of,
• Its slow onset (10 days for maximum effects)
• Consistent potency – Lower risk of cardiac arrhythmias).
• Long duration of action (2 – 3 weeks).
• Low cost and high cost-effectiveness.
• Easy laboratory monitoring of serum levels.
LIOTHYRONINE SODIUM (𝐓𝐓𝐓𝐓)
Available as tablets and injections.
𝐓𝐓𝐓𝐓 is not recommended now because,
• Its rapid onset (maximum effects within 24 hours)
Piyumal Fernando 2
Thyroxine and anti-thyroid medicines
1.Recapitulate the basic physiology of synthesis, storage and release of thyroxine.
2. Identify the common presentations of thyroid disorders.
3. Describe the pharmacological principles of management of thyroid disorders.
4. Classify medicines used in the management of hyperthyroid states giving examples.
5. Explain pharmacodynamics, pharmacokinetics, dosage forms and routes, indications, therapeutic efficacy, adverse
effects, cautions, contraindications, interactions with medicines, cost and availability of medicines used in thyroid
disorders including; • hypothyroidism • hyperthyroidism
6. Critically appraise the differences between the different treatment modalities used in the management of
hyperthyroid states.
7. Describe the principles of management of thyroid emergencies.
8. Discuss the safe use of thyroxine and anti-thyroid medicines in special populations including pregnancy.
9. Advice patients who are prescribed medicines for thyroid disorders.
Synthesis, storage and release of thyroxine
Main steps
1) uptake of plasma iodide by the follicle cells
2) oxidation of iodide
3) iodination of tyrosine residues of thyroglobulin
4) secretion of thyroid hormone
Piyumal Fernando 1
, Thyroxine and anti-thyroid medicines Pharmacology
Medicines in hypothyroidism
𝐓𝐓𝟑𝟑 𝐓𝐓𝟒𝟒
Biological Activity More potent (about 4 times as T4) Less potent
Binding to plasma Weak Strong (15 times more tightly bound)
protein
Half-life 1-2 days in euthyroids 7 days in euthyroids
Onset of action Quick (maximum effects within 24 Slow (10 days for maximum effects)
hours)
Duration of action Short (1 week) Long (2 – 3 weeks)
• Not used routinely. • Routinely used for
Clinical Indications • Used in Emergency replacement therapy.
indications. Eg: Hypothyroid
Coma.
Indications
1. Hypothyroidism (Replacement therapy)
a. Congenital hypothyroidism
b. Acquired hypothyroidism (Myxoedema)
2. TSH suppression therapy for non toxic goitre (Pharmacotherapy)
3. After thyroidectomy for thyroid malignancy (Replacement therapy)
• Levothyroxine should not be used to treat obesity or as a hypo-cholesterolemic agent.
Preparations
LEVOTHYROXINE SODIUM (𝐓𝐓𝐓𝐓)
Available as tablets (100 µg, 50 µg, 25 µg) and injections.
𝐓𝐓𝐓𝐓 is preferred over 𝐓𝐓𝐓𝐓 because of,
• Its slow onset (10 days for maximum effects)
• Consistent potency – Lower risk of cardiac arrhythmias).
• Long duration of action (2 – 3 weeks).
• Low cost and high cost-effectiveness.
• Easy laboratory monitoring of serum levels.
LIOTHYRONINE SODIUM (𝐓𝐓𝐓𝐓)
Available as tablets and injections.
𝐓𝐓𝐓𝐓 is not recommended now because,
• Its rapid onset (maximum effects within 24 hours)
Piyumal Fernando 2
