Thyroxine and Antithyroids

Hormones:

• The word harmones is derived from hormao which means to excite or to rouse or set in motion.

• It is defined as a chemical substance which is formed in one organ or released from one group of cell and carried in blood stream to another organ or group of cell, to exert specific regulatory effect.

• The word hormones are secreted by endocrine gland.

• The word derived from Greek word endon=within and crinein = to set a part.

• Like vitamins, hormones are effective in very low concentration.

• They do not have any cumulative action as they are destroyed and excreted as soon as their function are over.

• Some hormones function quickly and are destroyed quickly e.g. adrenaline.

• Some work slowly and destroyed slowly e.g –Thyroxine. 

Classifications of Hormones:

A. Chemically hormones are classified as

Amino acid derivatives:-e.g. Thyroxine, Liothyronine.

Polypeptides:-e.g. Insulin, Oxytocin, Vasopressin 

Proteins: e.g. –growth hormones

Glycoprotein’s:-e.g.  FSH (follicle stimulating hormone, (LH) Leutinising hormones.

Steroids: e.g: Testosterone, Progesterone, And Oestradiol.

Miscellaneous:

a. Hormones are classified according to source (origin).

1. Thyroids hormones (hormones are secreted by thyroids gland) e.g. - Thyroxine, Liothyronine, calcitonin

2. Pituitary hormones:

• Hormones secreted by anterior pituitary: e.g. ACTH, TSH, FSH, LH, GH.

• Hormones secreted by posterior pituitary: e.g Oxytocin, Vasopressin 

3. Adrenal gland hormones:

• Secreted by cortex: e.g. - Glucocorticoids like Cortisone, Hydrocortisone Mineral corticoids like aldosterone

• Secreted by medulla: adrenaline

4. Pancreatic hormones:

• Secreted by alpha cell of islets of langerhans: -e.g. glucagon

• Secreted by beta cell of islets of langerhans: e.g. Insulin

5. Parathyroid hormones secreted by parathyroid gland

6. Hormones secreted by thymus gland – e.g Thymine

7. Hormones secreted by hypothalamus:

• Releasing factor for stimulation: e.g. Thyrotropin, (release TSH). Adrenocorticotrophin (release ACTH), leutotrophin releasing hormones etc.

• Releasing factor for inhibition of TSH, GH, FSH, etc.

Thyroxine

Structure of Thyroxine:

Chemical name: 4-hydroxy 3, 5 –di-iodo phenyl) 3, 5 –di-iodo L-tyrosine

Physical properties of Thyroxine:

• Its sodium salt is light yellow to buff coloured powder.

• It is odourless.

• It is tasteless.

• It is slightly soluble in water and alcohol.

• It is soluble in solution of alkali hydroxide and carbonates.

• It is levorotatory.

Chemical properties of Thyroxine:

• When Thyroxine solution in alcohol is boiled with sodium nitrite in presence of HCL it gives yellow colour which when made alkaline with dil ammonia solutions gives red colour.

Stability and storage of Thyroxine:

• It is hygroscopic but stable in dry air.

• It get discolored when exposure to light. Hence it is stored in tightly closed light resistant containers.

Uses of Thyroxine:

• To treat hypothyroidism.

• To suppress goiter.

• To treat cretinism

Pharmaceutical dosage forms: Throxine tablets

Brand names: Eltroxin, Roxil, Thyroglandin

Methimazole

Physical properties of Methimazole:

• It is white or pale buff crystalline powder.

• It having faint characteristic odour.

• It is freely soluble in water alcohol and chloroform

Storage: it is stored in well closed containers.

Uses of Methimazole:

• For long term control of hyperthyroidism such as grave disease

• For preparation of patients with hyperthyroidism prior to surgery.

• For temporary control of hyperthyroidism I ¹³¹ therapies.

Dosage forms: Methimazole tablets

Brand names: Tapazole.

Propylthiouracil

Physical properties of Propylthiouracil:

• It occurs as white or pale cream coloured crystal or crystalline powder.

• It is odourless.

• It has bitter taste.

• It is very slightly soluble in water, alcohol, and chloroform.

• It is soluble in alkali hydroxide.

Chemical properties of Propylthiouracil:

• When its saturated solution is boiled with a mixture of equal volume of freshly prepared solution of sodium nitroprusside, hydroxyl ammonium chloride and sodium carbonates it give greenish blue colour.

Storage: It is stored in well closed containers.

Uses: As under Methimazole.

Dosage forms:  Polythiouracil tablets

Brand names: Propacil