Cough mixtures

COUGHING HAS BEEN REPORTED TO be the single most common reason for a patient to visit the doctor. A study conducted in 1991 in Finland found that the most common cause of cough is acute viral airway infection, which by itself is generally transient self-limiting and does not require any treatment.

Coughing is a natural reflex mechanism that protects the respiratory tract against irritant materials. The irritant inhaled may be mechanical (dust), or chemical in nature (cigarette smoke). Coughing can also be initiated by the presence of mucous or phlegm which is common when someone is suffering a cold, alergic rhinitis or asthma. Coughing is therefore a useful natural response to expel irritant or harmful substances from blocking the airways.

A cough can be said to be either useful or useless. A useful or productive cough is one that effectively expels out the sputum, thereby clearing the breathing passages. In such a situation, suppressing the cough can actually do more harm because the sputum that is retained may block the smaller airways, promoting infection and delaying recovery.

Rationally, a productive cough should only be stopped if it is dangerous for the patinent (such as someone who has just undergone an eye operation) or when it is causing sleep disturbances and is exhausting to the patient.

A useless, non-productive or dry cough which is distressing to the patient, if not suppressed, can further increase the irritation of the air passages. Generally, in most instances, no medicine is required to treat acute cough unless there are other serious underlying causes.

Medicines used for threating cough depend on the nature of the cough and treatment is based mainly on signs and symptoms presented, ie to achieve symptomatic relief. Basically, there are two types to medicine: expectorants or mucolytics and cough suppressants.

Coughing can be reduced by expelling out the irritant and taking something to soothe the irritation. This group of cough medicine is called demulcents. Examples include sweets to promote salivation and soothe an inflamed throat. Commercially available demulcents in the form of "cough" lozenges may contain honey and peppermint. They have to therapeutic advantages over other forms of sweets except that these "cough" lozenges cost more.

Agents that encourage the production of phlegm, called expectorants, and those that alter the consistency of the phlegm or mucous secretion (mucolytics) by making the secretion easily removable are also commonly used.

Cough reflex originates from the brain and cough suppressants (anti-tussives) are used to dampen or inhibit this "cough centre," thereby reducing the coughing. Cough suppressants are mainly used for dry, non-productive cough and can be further divided into two types: narcotic and non-narcotic cough suppressants. The former can lead to problems of addition if not used properly.

Patients may claim that they derived benefit from using these cough medicines and do find that their symptoms are relieved, but there is no evidence suggesting that taking these drugs speeds up recovery or cure the cough. The benefits of using expectorants and mucolytics as cough remedies have been over-exaggerated and disputed. Experts agree that there is no rationale for their use and evidence to support their therapeutic efficacy is lacking.

According to the British National Formulary (BNF), an authoritative resource on medicines: "There is no evidence that any drug can specifically facilitate expectoration". And as in the case of mucolytics: "Few patients have been shown to derive much benefit from them." The marketing and sales of these cough remedies are therefore largely economic-driven and are not for the interest of efficient, effective and safe use of medicine of the public.

The number of remedies available over-the-counter for treating coughs worldwide are many. A commercial compendium (DIMS 1995, 3rd issue) lists more than 100 cough and cold remedies available locally. Most are syrup-based containing active ingredients, flavouring and colouring agents. Many would contain more that one active ingredient, which sometimes is contradictory in their pharmacological actions.

For example, a cough remedy may contain both an expectorant (for productive cough) and also a cough suppressant (for dry cough). This irrational types of product will only lead to patients receiving inappriate drugs. The United State Food and Drug Administration (FDA) states that the general population would not derive any benefit from a combination product containing more than three pharmacological groups.

While the use of most cough mixtures is not well supported, the use of cough suppressants can be useful if properly indicated. Generally, the use of cough suppressants for productive cough is not recommended because it will prevent normal elimination of sputum. This will prevent the patient from getting rid of the excess phlegm which may be infected and thus prolong the illness or chest infection. There is agreement among experts that there are a few cases when cough suppressants should be used.

According to the BNF: "The benefits of using cough suppressants for treatment of cough are limited. One use, for exampel, is if sleep is disturbed by a dry cough. This is becuase cough suppressants may cause sputum retention and this may be harmful to patients with chronic bronchitis (inflammation of the bronchi) and bronchiectasis (dilation of a bronchus or bronchi).

"Conditions such as acute bronchitis and pneumonia are best treated with antibacterial drugs. Cough suppressants such as codeine, dextromethorphan and pholcodine are seldom sufficiently potent to be effective and tend to cause constipation.

The use of cough suppressants containing codeine and other narcotic analgesics is not generally recommended in children and should be avoided altogether in those under one year of age".

The World Health Organisation (WHO), under its Essential Drug List, suggests that codeine is "the most efficacious anti-tussive in the treatment of acute and chronic cough caused by a variety of disease states." However, codeine can be subjected to abuse (especially among drug addicts) and recently has led to a number of seizures by the relevant authorities.

An exampel similar to codeine is dextromethorphan. Although it belongs to same therapeutic group as codeine, dextromethorphan has been described as the "safest anti-tussive available" and "as effective as codeine except for severe acute cough."

The writer is a pharmacist lecturing at Universiti Malaya. She is a contributing author to the National Poison Centre, Universiti Sains Malaysia.