1. A ppt on THYROID HORMONESAND THYROID INHIBITORS By
Dr.Nanita Agrawal, Dr. Prashant ,MD
Pharmacology4students.com
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2. THYROID HORMONESAND THYROID INHIBITORS
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I. THYROID HORMONE
INTRODUCTION
The thyroid hormone secretes 3 hormones:
1. Thyroxine (T4)
2. Tryiodothyronine (T3)
3. Calcitonin
Former 2 are produced by thyroid follicles.
Calcitonin produced by interfollicular ‘c’ cells.
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B. ACTIONS
Growth and development: Essential for normal growth and development.
Intermediary metabolism: Marked effect on lipid, carbohydrate and proteinmetabolism.
Calorigenesis: Increase BMR.
CVS: Heart rate, contractility and output are increased.
GIT: Propulsive activity increased.
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Nervous system: Mental retardation is the hallmarkof cretinism.
Skeletal muscle: Muscles flabby and weak in myxoedema.
Kidney: Rate of urine flow is often increased.
Haemopoiesis: Facilitatory to erythropoiesis.
Reproduction: Indirect effect on reproduction.
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C. MECHANISM OF ACTIONS
T3 (and T4) penetrate cells.
Combine with a nuclear receptor.
A specific DNA sequece called ‘thyroid hormone response element’ has been identified.
T3-receptor complex binds.
Derepression of gene transcription
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D. PREPRATIONS
1-thyroxin sod:
Electroxin
Roxin 100 ug tab.
Thyranorm
Thyrox 25 ug, 50 ug, 100 ug tabs.
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E. USES
Cretinism: Due to failure of thyroid development. Detected during infancy or childhood. Mental retardation.
Adult hypothyroidism: Develops as a consequence of thyroiditis, thyroidectomy, treatment with goiterogens; may accompany simple goiter if iodine.
Myxoedema coma:
Thyroid nodule:
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Nontoxic goiter: May be endemic or sporadic.deficient production of thyroid hormone leads to excess TSH-throid enlarges.
Papillary carcinoma of thyroid:
Empirical uses:
Refractory anaemias
Menstrual disorders, infertility not corrected by usual treatment.
Chronic/ non healing ulcers
Obstinate constipation
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2. THYROID INHIBITORS
INTRODUCTION
Drugs used to lower the functional capacity of the hyperactive thyroid gland.
Throtoxicosis
Two main causes are Grave’s disease and toxic nodular goiter
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B. CLASSIFICATION
Inhibit hormone synthesis (Antithyroid drugs) propylthiouracil, methimazole, carbimazole.
Inhibit iodide trapping (ionic inhibitors) thiocynates (-SCN) , perchlorates (-C1O4), nitrates (-NO3).
Inhibit hormone release iodine, iodides of Na and K, organic iodide.
Destroy thyroid tissue Radioactive iodine .
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3. ANTITHYROID DRUGS
INTRODUCTION
Inhibit iodination of tyrosine residues in thyroglobulin.
Inhibit coupling of iodotyrosine residues to form T3 and T4.
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B. PHARMACOKINETICS
Quickly absorbed orally
Cross placenta
Metabolised in liver
Excreted in urine
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C. ADVERSE EFFECTS
Hypothyroidism due to over treatment common but reversible.
G.I. Intolerance, skin rashes and joint pain.
Loss or graying of hair, loss of taste, fever and liver damage.
Agranulocytosis
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15. D. PREPARATIONS AND DOSE
Propyltjiouracil : mg TDS followed by mg BD-TDS for maintenance PTU 50 mg tab.
Methimazole: 5-10 mg TDS initially, maintenance dose 5-15 mg daily in 1-2 divided doses.
Carbimazole: 5-15 mg TDS initially, maintenance dose mg daily in 1-2 divided doses, neo mercazole, thyrozole, antithyrox 5 mg tab. Carbimazole is more commonly used in india.
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E. USES
The following strategies are adopted:
Definitive therapy: Preferred in young patient with a short history.
Preoperatively: Carbimazole before performing partial thyroidectomy.
Along with 131 I.
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17. F. ADVANTAGES OVER SURGERY
No surgical risk
Hypothyroidism, if induced, is reversible.
Can be used even in children and young adults.
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G. DISADVANTAGES
Prolonged treatment is needed.
Not practicable in uncooperative/ unintelligent patient.
Drug toxicity.
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4. IODINE AND IODIDES
INTRODUCTION
Inhibition of hormone release- ‘thyroid constipation’.
B. PRERARATION AND DOSE
Lugol’s solution
Colloid iodine 10%
Collosol
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C. USES
Preoperative preparation
Thyroid storm
Prophylaxis of endemic goiter
Expectorant
Antiseptic
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D. ADVERSE EFFECTS
Acute reactions: Swelling of lips. Eyelids, angioedema of larynx (may be dangerous), fever, joint pain.
Chronic overdose (iodism): Long term use of high doses can cause hypothyroidism and goiter.
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5.RADIOACTIVE IODINE
INTRODUCTION
131I: Physical half life 8 days- most commonly used.
123I: Physical half life 13 hours- only rarely used diagnostically.
125I: Physical half life 60 days.
131I emits x-rays as well as B particles.
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B particles utilized for their destructive effect on thyroid cells.
131I is concentrated by thyroid.
Incorporated in colloid- emits radiation from within the follicles
Thyroid follicular cellsundergo pyknosisand necrosis followed by fibrosis.
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Diagnostic u curie is given.
Therapeutic
Average therapeutic dose is 3-6 m curie.
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B. ADVANTAGES
Treatment is simple, conveniently inexpensive.
No surgical risk, scar or injury to parathyroids/ recurrent laryngeal nerves.
Cure is permanent.
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C. DISADVANTAGES
Hypothyroidism
Long latent period of response.
Contraindicated during pregnancy- cretinism.
Not suitable for Young patients.
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6. B ADRENERGIC BLOCKERS
Propranolol
During thyrotoxic crisis.
While awaiting response to carbimazole or 131I.
Along with iodide for preoperative preparation before subtotal thyroidectomy.
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