Antitussives – Cough is a protective reflex. It helps in the expulsion of respiratory secretion or foreign particles from air passages. Stimulation of mechano-or chemoreceptors in throat, respiratory passages or stretch receptors in the lungs leads to cough.
Antitussives
Cough suppressant agents are called antitussives. These drugs act:
• By raising the threshold of cough centre in the central nervous system
• By reducing tussal impulses in the respiratory tract peripherally
• By both peripheral and central action
They are employed to depress the cough reflex in acute bronchitis, pneumonia, chronic bronchitis and bronchiectasis. They induce symptomatic relief of cough. They do not cure the underlying pathology. In fact they are not needed if antibacterial therapy is started promptly. Clinically used antitussives agents are:
• Opiolds: Codeine(10—30 mg) and pholcodeine(10 mg)
• Non-opioids: Dextromethorphan (10—20 mg), noscapine (15—30 mg), carbetapentane (30 mg), chlophedianol (20—40 mg) and pipazethate (40—80 mg)
Codeine is the most widely used narcotic antitussive. Dextromethorphen, pholcodeine, noscapine and methadone are other narcotic antitussives agents. They are used as linctus 3 to 4 times daily. They are useful in dry cough. Dextromethorphan is not an analgesic and causes less drowsiness and constipation than codeine.
Expectorants (Mucokinetics)
Antitussives are used to expel the mucous from the air passage by increasing bronchial secretion or reducing its viscosity. Ammonium chloride (0.3 to 1 g), ipecauanha (25—1 00 mg), potassium iodide (0.3 g) and squill (0.3 to 2 ml), tolu balsum (0.3—0.6 g), vasaka syrup (2—4 ml), terpin hydrate (0.1—0.3 ml), guaiacol (100—200 mg) sodium and potassium citrate or acetate (0.3—1 g) are commonly used expectorants.
Although expectorants do not have any useful role, several combinations of expectorants, cough suppressants and sedatives are marketed. Expectorants are useful in children and in bronchial asthma.
Mucolytic antitussives
To liquefy sputum and facilitate expectoration mucolytic agents are employed. Bromhexine, acetylcysteine, methylcysteine, and carbocysteine are commonly used mucolytics. However, simple inhalation of steam can be more effective to liquefy the sputum. Acetylcysteine (10—20%) is used as an inhalation.
It may cause nausea, fever, stomatitis and bronchospasm in certain individuals. Although bromhexine can be given orally, intravenously or by inhalation, it is usually administered orally in a dose of 8—16 mg 3 times daily.
Nasal Decongestants antitussives
Allergic rhinitis, hay fever and sinusitis cause mucosal congestion, which can be relieved by nasal decongestants. Sympathomimetics are generally used for this purpose. They give relief to the nasal obstruction by producing vasoconstriction of mucosal blood vessels and decreasing the thickness of the swollen nasal mucosa.
However, there occurs rebound after congestion with most of the sympathomimetic antitussives. So they cause chronic rhinitis on prolonged use. Some of them may show systemic effects and local irritation. They are contraindicated in young children.
Naphazoline, oxymetazoline, phenylephrine and xylometazoline are commonly used nasal antitussives. They are more potent, have long duration of action and likely to cause less rebound nasal congestion than ephedrine, which is also used as nasal decongestant.
Xylometazoline and oxymetazoline are less liable to induce tolerance. These agents are used in 0.5% (ephedrine), 0.1% (xylometazoline) solution as nasal drops. Ephedrine and pseudoephedrine are also given orally as nasal antitussives.
They are often combined with antihistaminics, antipyretics, analgesics, and antitussives for the relief of cold and other upper respiratory conditions. However, these preparations are of doubtful value.
Antitussives (cough suppressants) induce symptomatic relief of cough by depressing the cough reflex in acute bronchitis, pneumonia, chronic bronchitis, and bronchiectasis.
Codeine (most widely used), dextromethorphen, pholcodeine, noscapine and methadone are narcotic antitussives while benzonatate is non-narcotic antitussive.
Ammonium chloride, ipecauanha, potassium iodide and squill are expectorants which are used to expel the mucous from the air passage.
Bromhexine, acetylcysteine, methylcysteine and carbocysteine are commonly used mucolytics which liquefy sputum and facilitate expectoration.
As nasal drops, nasal decongestants (naphazoline, oxymetazoline, phenylephrine and xylometazoline) relieve the nasal obstruction by producing vasoconstriction of mucosal blood vessels and decreasing the thickness of swollen nasal mucosa. Ephedrine and pseudoephedrine are also given orally as nasal decongestants. Disadvantage with these preparations is rebound after congestion.
