The following points highlight the five major drugs used for the suppression of cough. The drugs are: 1. Expectorants 2. Mucolytic 3. Cough Suppressants 4. Demulcents 5. Antitussives.
Drug # 1. Expectorants:
Expectorants are drugs that promote expulsion of bronchial secretions. The bronchial glands are supplied by vagus nerve and when nausea or vomiting occurs there is widespread vagal activity and a considerable increase in bronchial and salivary secretion. The assumption that mixtures containing sub-emetic doses of drugs like ammonium chloride, ipecacuanha, guaiphenesin and squill facilitate expectoration is incorrect, though they may serve a placebo effect.
Steam inhalation containing benzoin tincture, menthol or eucalyptus and mucolytic drugs by reducing sputum viscosity serves as very useful expectorants in chronic lung infections, though the antibiotics have declined their use.
Drug # 2. Mucolytics:
Bromhexine, carbocisteine and mecysteine reduce sputum viscosity. They are taken orally 3 to 4 times daily and may be very effective expectorants in chronic asthma, bronchitis, and bronchiectasis in cleaning of the air passages. These drugs may cause occasional GIT irritation and rashes and are contraindicated in active peptic ulceration.
Drug # 3. Cough Suppressants:
Suppression of cough may be useful where there is no identifiable cause and the cough is unproductive, is tiring to the patient and disturbs the sleep. However, undue suppression of cough may cause sputum retention and this may be harmful in patients with chronic bronchitis and bronchiectasis.
Drug # 4. Demulcents:
Cough arising from irritation of the upper respiratory tract are helped by demulcents. Demulcent cough preparations contain soothing substance such as glycerol, diphenhydramine (Benadryl) or brompheniramine (antihistaminic) and menthol in the form of syrup. The benefit from such preparations is from the sedative action of antihistamine and the soothing effect of the syrup.
Drug # 5. Antitussives:
These are opioids that depress the cough center. Codeine depresses the cough centre. It can cause constipation and drug dependence. Pholcodine has practically no analgesic or addicting property, and has fewer side effects and is as effective as codeine as an antitussive. Opioids are generally used in the form of linctus (oral solution 5-10 ml 3-4 times daily, 5 ml contain 15 mg of codeine phosphate or 5 mg of pholcodeine). Dextromethorphan is a selective nonopioid antitussive with no narcotic, analgesic or addicting actions. It is as potent as codeine as a cough suppressant and, like codeine, can cause constipation.