Expectorants & emetics

Expectorants “Drugs that help in removing sputum from the respiratory tract. -either by increasing the fluidity (or reducing the viscosity) of sputum or -increasing the volume of fluids that have to be expelled from the respiratory tract by coughing.”

Both the action and mechanism of expectorants have been questioned and remain controversial. However, these may serve a placebo role and help the patient Ammonium chloride Potassium iodide Sodium iodide .

Dose related side-effects If the patient is sensitive, dose of expectorant is high enough, this may induce vomiting (emetic action). Hence, it is advisable to give the doses of expectorants that could be tolerated (by the patient) along with other pharmaceutical aids (flavours, sweetners, etc.) and cough suppressants.

Classification of Expectorants According the their mechanism of action… (1) Sedative type (2) Stimulant type

Sedative expectorants These are stomach irritant expectorants which are able to produce their effect through stimulation of gastric reflexes. e.g. Bitter drugs – Ipecac, Senega, Indian Squill Compounds – Antimony potassium tartrate, Ammonium chloride, Sodium citrate, Potassium iodide, etc.

Stimulant type 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 in respiratory tract and sputum is diluted. e.g. - Eucalyptus, lemon, anise - Active constituents of oil like terpine hydrate, anethole

Emetics These are the drugs which give rise to forced regurgitation (emesis) by which the contents of the stomach get expelled through the oral cavity. They are very important in cases of poisoning.

Mechanism of action The emetics act by.. - either by local irritation of gastric mucosa. e.g. Ammonium bicarbonate, ipecacuanha - or directly on the chemoreceptor trigger zone (i.e. centrally acting emetics).

Although vomiting is primarily considered to be a respiratory function, its ultimate result would cause the evacuation of the stomach. Emetics are sometimes added to cough preparations in low doses to stimulate flow of respiratory tract secretions.

Clinical facts… There are certain types of poisoning in which the toxic substances themselves may be able to induce emesis by reflex action. There are some types of poisoning in which poisons may remain in stomach for sometime before entering intestine where they may get absorbed. Before this occurs, emetics are given to patients for physically expelling the toxic substances and reduce the harmful effects and may be able to save patient’s life. When a patient is in unconscious state, emetics may not be very useful and gastric lavage may be required.

2NaCl + (NH4)2SO4  2NH3 + HCl + Na2SO4 Ammonium chloride Molecular formula: NH4Cl Preparation: (i) Commercially, it is prepared by neutralising NH3 with HCl. NH3 + HCl  NH4Cl (ii) It is produced by heating ammonium sulphate with NaCl 2NaCl + (NH4)2SO4  2NH3 + HCl + Na2SO4

Ammonium chloride Properties: - White coloured fine or coarse crystalline powder - Cooling saline taste - Slightly hygroscopic - Partialy soluble in mixture of water & alcohol - Freely soluble in glycerine - 0.8% w/v of NH4Cl is isotonic with serum. - Freshly prepared aqueous solutions are neutral to litmus but become quickly acidic on standing because of hydrolysis.

Ammonium chloride Assay: It was previously assayed by precipitation titration by using the Volhard’s method. Now, it is assayed by acid-base titration method. Uses: (1) It acts as mild expectorant and diaphoretic when administered in small doses. It does so due to local irritation which produces increasing secretion of respiratory tract, and makes the mucus less viscous. NH4Cl and NH4HCO3 are therefore used in cough preparations.

Ammonium chloride (2) It acts in maintaining acid-base equilibrium of body fluids. (3) It is also used as diuretic in combination with mercurial compounds. The diuretic effect is because of utilization of NH4+ cation in conversion into urea and in the process portion H+ and Cl- ions are formed. The H+ ion reacts with bicarbonate and CO2 and water is produced. On continue use, it increases acidity of urine and metabolic acidosis is produced. Thus, it can be useful in some cases of systemic alkalosis.

Ammonium chloride Dose: As systemic acidifier : 1-2 g four times a day As expectorant : 0.3-0.5 g Storage: It is stored in tightly closed container

Antimony potassium tartrate Synonym: Tarter emetic Molecular formula: C4H4KO7Sb Structural formula: KOOC-CHOH-CHOH-COO(SbO) Properties: - Colourless crystals - Odourless - Sweetish taste - On exposure to air, crystals effloresce - Solubility : 1 in 12 (Water at 25°C) - Insoluble in alcohol and soluble in glycerin

Antimony potassium tartrate Preparation: It is obtained by mixing 5 parts of antimony trioxide (Sb2O3) with 6 parts of potassium acid tartrate in a fine paste. Keep this paste aside for a day. Boil it with water for 15 minutes with constant stirring. The liquid is then filtered and left for crystallization 2KHC4H6O6 + Sb2O3  2K(SbO)C4H4O6 + H2O

Antimony potassium tartrate Assay: Iodimetric titration using starch indicator Uses: - As an expectorant and emetic (hence named- ‘tartar emetic’) - The emetic action is because of irritant action on the gastric mucosa. The emetic action has slow onset and marked depression can follow. - It can also be used to treat schistosmiosis (drug of choice in infections produced by Schistosoma japonicum).

Copper sulphate Synonym: Cupric sulphate, Blue vitriol Molecular formula: CuSO4.5H2O Molecular weight: 249.7 Preparation: 2Cu + 2H2SO4 + O2  CuSO4 + H2O Assay: - Iodometric titration (oxidation-reduction method)

Copper sulphate Burette : 0.1N Na2S2O3 solution Iodine flask : 5 ml of CuSO4 (sample soln) + 5 ml of CH3COOH + 5 ml of KI + 10 ml of distilled water + 0.5 ml of starch mucilage + 5 ml of KCNS Indicator : Starch mucilage End-point : Brown – yellow – blue - colourless

Copper sulphate Uses: - As an emetic (in dose of 300mg in 30ml of H2O). However, its use as an emetic can be dangerous because of large and corrosive doses. - As chemical antidote in phosphorus poisoning. - As an astringent and also as a fungicide (1.5% solution). - It is an ingredient of Benedict’s reagent and Fehling’s reagent.