Normal cough is a protective physiological reflects (both voluntary and involuntary) to clear the Airway.
Expectorants are drug used to help in the removal or expulsion of the secretion or exudate from the trachea, bronchi, or lungs and hence they are used in the treatment of cough.
Mechanism of Expectorants
Expectorant act on the respiratory tract in two ways
- By decreasing the viscosity of bronchial secretion and facilitating their elimination from trachea.
- By increasing the amount of respiratory tract fluid, a demulcent action is exerted on dry mucosal lining, thus relieving the unproductive cough.
Classifications of expectorants
It is possible to classify expectorants in according to their mechanism of action into two categories, viz.
i) sedative type
ii) stimulant type.
These are stomach irritant expectorants which are able to produce their effect through stimulation of gastric reflexes. Examples of sedative expectorants include bitter drugs such as ipecac, senega, Indian squill, and compounds such as antimony potassium tartrate, ammonium chloride, sodium citrate, potassium iodide, etc.
These are the expectorants which bring about a stimulation of the secretory cells of the respiratory tract directly or indirectly. Since these drugs stimulate secretion, more fluid gets produced in respiratory tract and sputum is diluted.
Examples of stimulant expectorants include drugs such as eucalyptus, lemon and active constituents of oil like terpine hydrate, anethole.
Example of Expectorants
Inorganic saline expectorants are
- Ammonium chloride/ Ammonium salt
- Iodide(potassium iodide/ sodium iodide)
- Antimony potassium tartrate
Any emetic is a drug which induce vomiting. Emetic act either directly by stimulation of the chemoreceptor trigger zone located in medulla oblongata thoda or refluxing by irritant action on the gastrointestinal tract.
Sometime, emetics in law doses are used in cough preparation. They probably stimulate flow of respiratory tract secretions.
Example of emetics
Inorganic compounds used as emetics are
- Copper sulphate
- Sodium chloride
- Zinc sulphate
- Antimony potassium tartrate
Note: Clinically in these days, emetics are replaced bye stomach tube, a safer and more effective tool for emptying the stomach.
1. Ammonium chloride
M.F.: NH4Cl; Mw: 53.49
Synonyms: Ammonium Muriate, Sal Ammoniac, Salmic, Amchlor, Ammon. Chlor.
It is prepared by neutralizing hydrochloric acid with ammonia
HCL + NH3 → NH4Cl ( Ammonium chloride )
- White crystalline, odourless powder with saline taste.
- It is hygroscopic.
- Freely soluble in water.
Weighed amount is dissolved in water and treated with pre-neutralised formaldelyde solution. The ammonium chloride is decomposed to methyleneimine and an equivalent amount of hydrochloric acid. The liberated acid is titrated with standard NaOH using phenolphthalein indicator
Hygroscopic so stored in tightly closed containers.
- Expectorant (dose 300 mg to 1000 mg)
- Systemic acidifier
2. potassium iodide
M.F.: KI; Mw: 166.01
Synonyms: Kalii Iodidum
It is prepared by the action of potassium hydroxide on iodine, potassium. Iodate is converted to Iodide.
6 KOH + 3I2 → KIO3 + 5KI + 3H2O
KIO3 + 3C → KI + 3CO
- Colourless, crystalline or white powder.
- Odourless with slight bitter taste, soluble in water, glycerin and in alcohol.
- On standing becomes yellow particularly exposed to light due to the liberation of free iodine.
- Iodine dissolved in an aqueous solution of potassium iodide forming a dark brown solution containing potassium tri-iodide.
KI + I2 → KI3 (potassium tri-iodide)
It is assayed by titration with potassium iodate. It is dissolved in water, conc. HCl is added into it and is then titrated with a standard potassium Iodate solution.
KIO3 + 5KI + 6 HCl → 6 KCl + 3I2 + 3H2O
KIO3 + 2I2 + 6 HCl → KCl + 5I Cl + 3H2O
- Source of Iodine
- Antifungal in veterinary preparation
- Ingredient of Iodine solution
ANTIMONY POTASSIUM TARTRATE
M.F. C4H4KO7 Sb;
Syn : Taster emetic
It is prepared by mixing antimony trioxide with potassium acid tartrate. It is then boiled for few mts. Then the liquid is filtered and dried.
2 KHC4H4O6 + Sb2O3 → 2K (SbO) C4H4O6 + H2O
- Colorless, odorless crystals having sweet taste.
- It is soluble in water but insoluble in alcohol.
- On exposure to air, crystals effloresces.
Assay: Iodometric Method
Weighed amount is dissolved in water, small amount (about 2g) of sodium bicarbonate is added. Then it is titrated with iodine using starch mucilage as indicator.
2 C4H4O7 Sb K + 3H2O + I2 → 2K H C4H4O6 + Sb2 O5 + 4 HI
It is stored in air tight container.
- to treat schistosomiosis.
- It is acting as an emetic.
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