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Transcript of A ppt on THYROID HORMONESAND THYROID INHIBITORS By Dr.Nanita Agrawal, Dr. Prashant,MD...
A ppt on
THYROID HORMONESAND THYROID INHIBITORS
By Dr.Nanita Agrawal, Dr. Prashant ,MD
1dr prashant's
www.pharmacology4students.com
THYROID HORMONESAND
THYROID INHIBITORS
dr prashant's www.pharmacology4students.com
I. THYROID HORMONEA. 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.
3dr prashant's www.pharmacology4students.com
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.4dr prashant's
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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 6dr prashant's
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D. PREPRATIONS
• 1-thyroxin sod:
Electroxin
Roxin 100 ug tab.
Thyranorm
Thyrox 25 ug, 50 ug, 100 ug tabs. 7dr prashant's www.pharmacology4students.com
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: 8dr prashant's
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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 anaemiasMenstrual disorders, infertility not
corrected by usual treatment.Chronic/ non healing ulcersObstinate constipation
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2. THYROID INHIBITORS
A. 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 .11dr prashant's
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3. ANTITHYROID DRUGS
A. 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 14dr prashant's www.pharmacology4students.com
D. PREPARATIONS AND DOSE
• Propyltjiouracil : 50-150 mg TDS followed by 25-50 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 2.5-10 mg daily in 1-2 divided doses, neo mercazole, thyrozole, antithyrox 5 mg tab. Carbimazole is more commonly used in india. 15dr prashant's
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E. USES
• The following strategies are adopted:
1) Definitive therapy: Preferred in young patient with a short history.
2) Preoperatively: Carbimazole before performing partial thyroidectomy.
3) Along with 131 I. 16dr prashant's www.pharmacology4students.com
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
A. 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 20dr prashant's www.pharmacology4students.com
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
A. 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.22dr prashant's
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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 25-100 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.26dr prashant's
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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.27dr prashant's
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