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11. Drugs Used to Treat Coughs
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14th of February, 2010

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Coughs frequently serve a useful purpose, for example, to get rid of an inhaled foreign body or to cough up sputum. These coughs are said to be productive. A cough which is just dry and irritating is said to be unproductive and serves no purpose. As with cold remedies the marketing of cough medicines is a lucrative business and so the market is flooded with preparations. Many of these are mixtures containing such small doses of individual drugs as to render them pharmacologically ineffective. But, of course, a large proportion of us respond to inert mixtures – some of us responding better to one colour or taste than to others.

The aim of using cough medicines is to give comfort to those people with a productive cough and to help them cough up their sputum. For those people with a dry, irritating, unproductive cough, the aim is to suppress it. We therefore have two main groups of drugs which are used to treat coughs – expectorants and cough suppressants. Expectorants are given with the aim of liquefying the sputum, so that it is easier to cough up. Cough suppressants either work locally at the site of the irritation in the throat or they act on the cough centre in the brain, reducing the desire to cough. Some cough mixtures contain drugs which act on the conscious part of the brain producing drowsiness and therefore making you less aware of the irritation in your throat.

Expectorants

These act by irritating the lining of the stomach which by reflex stimulates the nerves supplying the glands in the bronchi. This is said to result in an increased production of secretions thus making the sputum more watery and easier to cough up. However, the dose required to do this would, with most of these drugs, produce stomach pains and vomiting. They include ammonium chloride, acetates, acetic acid, benzoin compounds, bicarbonates, creosote, eucalyptus, ipecacuanha, menthol, peppermint, potassium iodide, sodium benzoate, sodium citrate, tolu and guaiacols (e.g. guaifenesin). They are present in many cough medicines, and from the point of view of effectiveness you may as well choose them by taste or colour.

The stickiness of sputum depends on its degree of water content, which in turn depends upon the general degree of hydration of the body. Patients with chronic bronchitis and other chest disorders which produce dry sticky sputum may well benefit from increasing their fluid intake. Inhalation of water or steam may also be very useful and it does not really matter whether these are made to smell pleasant by the addition of menthol, eucalyptus or benzoin.

Drugs that Dissolve Sputum (Mucolytic Drugs)

Some drugs have been shown to ‘digest’ sputum in the laboratory, but their effect upon sputum in the bronchial tubes has been variable. Cysteine compounds, e.g. carbocisteine (Mucodyne) and mecysteine (Visclair) by mouth may liquefy sputum and help patients with cystic fibrosis to cough up phlegm. Dornase alfa (Pulmozyme) is a bioengineered human enzyme that dissolves sputum. It is given by inhalation using a jet nebulizer in patients with cystic fibrosis.

Cough Suppressants (Antitussives)

The most important cough suppressant in people who smoke is to stop smoking. For coughs which are caused by irritation or inflammation in the throat above the larynx (voice-box) there are many different makes of soothing cough preparation; they include sweets, pastilles, lozenges, cough drops and linctuses. A few contain antiseptics (such as benzoin, cetylpridinium, chloroxylenol, creosote, domiphen, thymol) in doses which are totally useless but which, if given in effective antiseptic doses, could be harmful.

Most cough sweets contain demulcents, which are soothing substances which act on the surface of the throat, e.g. honey, liquorice, glycerin. Such preparations also contain pleasant-smelling and tasting substances, like peppermint, eucalyptus, cinnamon, lemon, clove, aniseed. Others contain menthol, camphor, chloroform. The main effect of these preparations is that their smell or taste may help you feel better. They may increase the production of saliva, which is soothing and helps to wash the inflamed surfaces of the throat. Some preparations contain a topical anaesthetic (e.g. benzocaine), which may reduce the pain of inflammation. Cough medicines which contain the same ingredients in liquid form are even more irrational since they are swallowed directly into the stomach and only have a fraction of a second to work locally on the throat. There is no evidence that any of these cough preparations are any more effective than sucking ordinary sweets or chewing gum.

For non-productive irritating coughs caused by inflammation below the larynx, steam inhalations may be very useful and can be made to smell nice by adding substances such as menthol.

Opiate Cough Suppressants

Powerful opiate drugs reduce the sensitivity of the cough centre in the brain. They are used to suppress severe coughs (e.g. in cancer of the lung). They include diamorphine (heroin), methadone (Physeptone) and morphine. These are discussed in Chapter 30. They also tend to dry up and thicken bronchial secretions. These drugs can cause addiction.

Codeine is a much less powerful opiate than morphine. In appropriate dosage it may help to suppress a dry or painful cough but not a severe cough. It may cause constipation and regular daily use may, very rarely, produce addiction.

Milder opiate cough suppressants include pholcodine and dextromethorphan (present in many cough mixtures). They are less constipating and less effective but they are not addictive.

Cough medicines containing codeine or some other opiate should be used with utmost caution in children and not in infants under one year of age.

Cough Mixtures

In addition to containing small doses of a cough suppressant and/or an expectorant many of these mixtures contain soothing substances (demulcents) such as sorbitol, glycerol, syrup and flavourings, for example, peppermint, eucalyptus, lemon, clove, aniseed and menthol.

Some compound cough medicines contain antihistamines. Yet there is doubt about their benefits. They may dry the surface of the upper respiratory tract. Cough medicines that contain a sedative antihistamine, e.g. promethazine and diphenhydramine are used at night because they cause drowsiness but see warnings on antihistamines in A–Z of Medicine.

Selecting a Cough Medicine

For a dry or painful throaty cough (i.e. caused by inflammation or irritation above the larynx) anything that may be sucked will help. If the cough is very irritating it may help to take a dose of codeine linctus along with something to suck or chew.

For a cough which is on the chest (below the larynx) which is dry and irritating, a single cough suppressant may help, e.g. linctus codeine or pholcodine. For the ordinary dry cough associated with a common cold only three or four doses at appropriate intervals will be required.

Products containing codeine and pholcodine include:

Codeine:  Pholcodine:
Benylin with Codeine Benylin Children’s Dry Cough
Boots Catarrh Cough Syrup Boots Children’s 1 Year Plus Night Time Cough Syrup
Dimotane Co Expulin
Dimotane Co Paediatric Expulin Dry
Famel Original Expulin Paediatric
Galcodeine Galenphol
Galcodeine Paediatric Galenphol Strong
Pulmo Bailly Hill’s Balsam Adult Expectorant
Robitussin Night-Time Hill’s Balsam Cough Suppressant
Nirolex Day Cold Comfort
Nirolex for Night Time Coughs
Pavacol D
Tixylix Cough and Cold
Tixylix Daytime
Tixylix Night-time

Steam inhalations are of benefit to both dry throaty coughs and to nonproductive chesty coughs. If you find yourself having to take a cough suppressant for more than a few days then see your doctor. Also see your doctor if the cough does not clear up after one or two weeks, if your sputum turns yellow or green (you may need an antibiotic), if there is blood in your sputum, if your cough is associated with chest pain and/or fever or if it is associated with breathlessness.

A chesty productive cough (i.e. when you cough up sputum) may be helped by warm drinks and/or steam inhalations, stopping smoking and avoiding dry, dusty atmospheres. Cough medicines are of little use.

Diamorphine (heroin), methadone and morphine are effective cough suppressants used to control coughs in patients suffering from lung cancer or other severe disorders.

Patients with kidney or heart disorders, or with raised blood pressure, or on a reduced sodium intake, should check the sodium content of any cough medicine that they purchase from their pharmacist.

Visitor Comments
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