BMA Concise Guide to Medicine & Drugs

RESPIRATORY SYSTEM

The respiratory system consists of the lungs and the air passages, such as the trachea (windpipe) and bronchi, by which air reaches them. Through the process of inhaling and exhaling air (breathing) the body obtains the oxygen necessary for survival, and to expel carbon dioxide, which is the waste product of the basic human biological process.

Air enters the trachea, which branches into two main bronchi, one for each lung. Within the lungs, the air passes into bronchioles, smaller tubes whose muscular walls may contract or dilate in response to drugs and nerve signals. The bronchioles open out into tiny, blood-vessel lined air sacs (alveoli), which allow oxygen to pass into the bloodstream and carbon dioxide to pass from the bloodstream for expiration.

WHAT CAN GO WRONG

Difficulty in breathing may be due to narrowing of the air passages, from spasm, as in asthma and bronchitis, or from swelling of the linings of the air passages, as in bronchiolitis and bronchitis. Breathing difficulties may also be due to an infection of the lung tissue, as in pneumonia and bronchitis, or to damage to the small air sacs (alveoli) from emphysema or from inhaled dusts or moulds, which cause pneumoconiosis and farmer’s lung. Smoking and air pollution can affect the respiratory system in many ways, leading to diseases such as lung cancer and bronchitis.

Sometimes difficulty in breathing may be due to congestion of the lungs from heart disease, to an inhaled object such as a peanut, or to infection or inflammation of the throat. Symptoms of breathing difficulties often include a cough and a tight feeling in the chest.

WHY DRUGS ARE USED

Drugs with a variety of actions are used to clear the air passages, soothe inflammation, and reduce the production of mucus. Some can be bought without a prescription as single- or combined-ingredient preparations, often with an analgesic.

Decongestants reduce swelling inside the nose, thereby making it possible to breathe more freely. If the cause of the congestion is an allergic response, an antihistamine is often recommended to relieve symptoms or prevent attacks. Bacterial infections of the respiratory tract are usually treated with antibiotics, although most respiratory tract infections are viral.

Bronchodilators are drugs that widen the bronchi. They are used to prevent and relieve asthma attacks. Corticosteroids reduce inflammation in the swollen inner layers of the airways. They are used to prevent asthma attacks. Other drugs, such as sodium cromoglicate, may be used for treating allergies and preventing asthma attacks but are not effective once an asthma attack has begun.

A variety of drugs are used to relieve a cough, depending on the type of cough involved. Some drugs make it easier to eliminate phlegm; others suppress the cough by inhibiting the cough reflex.

MAJOR DRUG GROUPS

· Bronchodilators

· Drugs for asthma

· Decongestants

· Drugs to treat coughs

· See also sections on Allergy and Infections

Bronchodilators

Air entering the lungs passes through narrow tubes called bronchioles. In asthma and bronchitis the bronchioles become narrower, either as a result of contraction of the muscles in their walls, or as a result of mucus congestion. This narrowing of the bronchioles obstructs the flow of air into and out of the lungs and causes breathlessness.

Bronchodilators are prescribed to widen the bronchioles and improve breathing. There are three main groups of bronchodilator: sympathomimetics, anticholinergics, and xanthine drugs, which are related to caffeine. They are all used for relief of symptoms, and do not affect the underlying disease process. Anticholinergics are thought to be more effective in, and are used particularly for, bronchitis. In chronic asthma, they are less effective, and are usually prescribed as additional therapy when control with other drugs is inadequate. Sympathomimetics are the first choice drugs in the management of asthma, and are frequently used in bronchitis. Xanthines have been used for many years, both for asthma and bronchitis. They usually need precise adjustment of dosage to be effective while avoiding side effects. This makes them more difficult to use, and they are reserved for people whose condition cannot be controlled by other bronchodilators alone.

WHY THEY ARE USED

Bronchodilators help to dilate the bronchioles of people suffering from asthma and bronchitis. However, they are of little benefit to those suffering from severe chronic bronchitis.

Bronchodilators are usually taken when they are needed in order to relieve an attack of breathlessness that is in progress. Some people find it helpful to take an extra dose of their bronchodilator immediately before undertaking any activity that is likely to provoke an attack of breathlessness. A patient who requires treatment with a sympathomimetic inhaler more than twice a week or at night should see his or her doctor about preventative treatment with an inhaled corticosteroid.

Sympathomimetic drugs are mainly used for the rapid relief of breathlessness; anticholinergic and xanthine drugs are used both for acute attacks and long-term.

HOW THEY WORK

Bronchodilator drugs act by relaxing the muscles surrounding the bronchioles. Sympathomimetic and anticholinergic drugs achieve this by interfering with nerve signals passed to the muscles through the autonomic nervous system. Xanthine drugs are thought to relax the muscle in the bronchioles by a direct effect on the muscle fibres, but their precise action is not known.

Bronchodilator drugs usually improve breathing within a few minutes of administration. Corticosteroids act more slowly and it may be several days before the capacity for exercise increases substantially. Eventually the corticosteroids should reduce the need for bronchodilators.

Because sympathomimetic drugs stimulate a branch of the autonomic nervous system that controls the heart rate, they may sometimes cause palpitations and trembling. Typical side effects of anticholinergic drugs include dry mouth, blurred vision, and difficulty in passing urine. Xanthine drugs may cause headaches and nausea.

RISKS AND SPECIAL PRECAUTIONS

Since most bronchodilators are not taken by mouth, but inhaled, they do not commonly cause serious side effects. However, because of their possible effect on heart rate, xanthine and sympathomimetic drugs need to be prescribed with caution to people with heart problems, high blood pressure, or an overactive thyroid gland. Smoking tobacco and drinking alcohol increase excretion of xanthines from the body, reducing their effects. Stopping smoking after being stabilized on a xanthine may result in a rise in blood concentration, and an increased risk of side effects. It is advisable to stop smoking before starting treatment. The anticholinergic drugs may not be suitable for people with urinary retention or those who have a tendency to glaucoma.

COMMON DRUGS

Sympathomimetics Bambuterol, Ephedrine, Epinephrine, Fenoterol, Formoterol, Salbutamol, Salmeterol, Terbutaline

Anticholinergics Ipratropium bromide, Tiotropium

Xanthines Theophylline/aminophylline

Drugs for asthma

Asthma is a chronic lung disease that is characterized by episodes in which the bronchioles constrict due to oversensitivity. The attacks are usually, but not always, reversible; asthma is also known as reversible airways obstruction. About 5 per cent of adults and 10 per cent of children have the disease. Sometimes the inflammation causing the constriction is due to an identifiable allergen in the atmosphere, such as house dust mites, but often there is no obvious trigger. Breathlessness is the main symptom, and wheezing, coughing, and chest tightness are common. Asthma sufferers often have attacks during the night and wake up with breathing difficulty. The illness varies in severity, at its most severe, it can even be life threatening.

There are a number of drugs that are used in the control of asthma. Where drugs are needed only to control an occasional attack, a sympathomimetic bronchodilator will probably be used in the form of an inhaler. When the patient needs continuous preventative treatment there are a number of choices: often an inhaled corticosteroid may be used (with a sympathomimetic inhaler if attacks persist). More severe cases may require higher-dose corticosteroids or the addition of a long-acting sympathomimetic bronchodilator. If this is not adequate, the addition of an anticholinergic drug, or theophylline, or these in combination with others already tried, may be needed. There are also leukotriene antagonists, which may be used alone or with corticosteroids; they are less effective in severe cases when patients are taking high doses of other drugs. Some people who suffer from very severe asthma may need such large doses of corticosteroids that tablets have to be taken. Antihistamines have been prescribed for asthma in the past but this has not proved to be a successful treatment.

WHY THEY ARE USED

In asthma, the airways (bronchioles) constrict, which makes it difficult to get air into or out of the lungs. Bronchodilators (sympathomimetics, anticholinergics, and theophylline) relax the constricted muscles around the bronchioles. Short-acting sympathomimetics act within a few minutes when inhaled and are used to provide relief of symptoms during an attack, and in more severe cases the long-acting sympathomimetics may be used to help with continuous protective cover. They are particularly useful for preventing symptoms overnight. Theophylline/aminophylline must be given by mouth or injection; the tablets are used for regular continuous dosing, and the injection is used in hospital to gain control of severe asthma. Drugs that are not bronchodilators, such as corticosteroids and leukotriene receptor antagonists, are effective for long-term protection. Corticosteroids are also given orally for severe acute attacks. Although they have a delayed onset of action (12–24 hours), they help to prevent a recurrence of symptoms in the days after the acute attack.

In some cases, an intravenous injection of magnesium sulphate may be given to treat a severe asthma attack.

HOW THEY WORK

Inhaling a drug directly into the lungs is the best way of obtaining benefit without experiencing excessive side effects. A selection of devices for delivering the drug into the airways is described here.

Inhalers or puffers release a small dose when they are pressed, but require some skill to use effectively. A large hollow plastic “spacer” can help you to inhale your drug more easily. Cartridges deliver larger amounts of drug than inhalers and are easier to use because the drug is taken in as you breathe normally.

In severe attacks, nebulizers pump compressed air through a solution of drug to produce a fine mist that is inhaled through a face mask. Nebulizers deliver large doses of the drug to the lungs, rapidly relieving breathing difficulty.

Bronchodilators act by relaxing the muscles surrounding the bronchioles. Corticosteroids are used for their anti-inflammatory properties. By suppressing airway inflammation they reduce swelling (oedema) inside the bronchioles, complementing relaxation of the walls by the bronchodilators in opening up the tubes. Reducing the inflammation also has the effect of reducing the amount of mucus produced, and this again helps to clear the airways. Corticosteroids usually start to increase the sufferer’s capacity for exercise within a few days, and most people find that the frequency of their attacks of breathlessness is greatly reduced.

Leukotrienes, which used to be called “slow reacting substances”, occur naturally in the body. They are chemically related to the prostaglandins, but are much more potent in producing an inflammatory reaction; they are also much more potent than histamine at causing bronchoconstriction. Leukotrienes seem to play an important part in asthma. Drugs have been developed that block their receptors (leukotriene receptor antagonists) and therefore reduce the inflammation and bronchoconstriction of asthma. Cromoglicate and nedocromil act by stabilizing mast cells in the lungs, preventing them from releasing histamine, leukotrienes, and other inflammation-causing chemicals.

RISKS AND SPECIAL PRECAUTIONS

The drugs taken by inhalation act locally and are used in much lower doses than would be needed as tablets. They do not commonly cause serious side effects, but the dry powder inhalations can cause a reflex bronchospasm as the powder hits the lining of the airways; this can be avoided by first using a short-acting sympathomimetic. Inhaled corticosteroids may encourage fungal growth in the mouth and throat (thrush). This can be minimized by using a spacer and by rinsing your mouth out and gargling after each inhalation. High doses of inhaled corticosteroids may suppress adrenal gland function, reduce bone density, cause bruising, increase the risk of glaucoma, and retard growth in children. Sympathomimetics and theophylline by mouth may affect heart rate, and should be prescribed with caution to people with heart problems, high blood pressure, or an overactive thyroid gland. The effects of theophylline may last longer if you have a viral infection, heart failure, or liver cirrhosis. The drugs also interact with many other drugs. Anticholinergics must be used with caution in patients who have prostate problems or urinary retention. Leukotriene receptor antagonists may rarely produce a syndrome with several potentially serious effects including worsening of lung function and heart complications.

COMMON DRUGS

Sympathomimetics Bambuterol, Ephedrine, Epinephrine, Fenoterol, Formoterol, Salbutamol, Salmeterol, Terbutaline

Anticholinergics Ipratropium bromide, Tiotropium

Leukotriene antagonists Montelukast, Zafirlukast

Corticosteroids Beclometasone, Budesonide, Ciclesonide, Fluticasone, Mometasone, Prednisolone

Xanthines Theophylline/aminophylline

Other drugs Nedocromil, Sodium cromoglicate

Decongestants

The usual cause of a blocked nose is swelling of the delicate mucous membrane that lines the nasal passages and excessive production of mucus as a result of inflammation. This may be caused by an infection (for example, a common cold) or it may be caused by an allergy (for example, to pollen – a condition known as allergic rhinitis or hay fever). Congestion can also occur in the sinuses (the air spaces in the skull), resulting in sinusitis. Decongestants are drugs that reduce swelling of the mucous membrane and suppress the production of mucus, helping to clear blocked nasal passages and sinuses. Antihistamines counter the allergic response in allergy related conditions. If the symptoms are persistent, either topical corticosteroids or sodium cromoglicate may be preferred.

WHY THEY ARE USED

Most common colds and blocked noses do not need to be treated with decongestants. Simple home remedies such as steam inhalation, possibly with the addition of an aromatic oil such as menthol or eucalyptus, are often effective. Decongestants are used when such measures are ineffective or when there is a particular risk from untreated congestion (for example, in people who suffer from recurrent middle-ear or sinus infections).

Decongestants are available in the form of drops or sprays applied directly into the nose (topical decongestants), or they can be taken by mouth. Small quantities of decongestant drugs are added to many over-the-counter cold remedies (see Cold cures).

HOW THEY WORK

When the mucous membrane lining the nose is irritated by infection or allergy, the blood vessels supplying the membrane become enlarged. This leads to fluid accumulation in the surrounding tissue and encourages the production of larger-than-normal amounts of mucus.

Most decongestants belong to the sympathomimetic group of drugs that stimulate the sympathetic branch of the autonomic nervous system. One effect of this action is to constrict the blood vessels, thereby reducing swelling of the lining of the nose and sinuses.

HOW THEY AFFECT YOU

When applied topically in the form of drops or sprays, these drugs start to relieve congestion within a few minutes. Decongestants by mouth take a little longer to act, but their effect may also last longer. Used in moderation, topical decongestants have few adverse effects, because they are not absorbed by the body in large amounts.

Used for too long or in excess, topical decongestants can, after giving initial relief, do more harm than good, causing a “rebound congestion”. This effect is a sudden increase in congestion due to widening of the blood vessels in the nasal lining because the blood vessels are no longer constricted by the decongestant. Rebound congestion can be prevented by taking the minimum effective dose and by using decongestant preparations only when absolutely necessary. Decongestants taken by mouth do not cause rebound congestion but are more likely to cause other side effects.

COMMON DRUGS

Used topically Ephedrine, Ipratropium, Oxymetazoline, Phenylephrine, Xylometazoline

Taken by mouth Ephedrine, Phenylephrine, Pseudoephedrine

Drugs to treat coughs

Coughing is a natural response to irritation of the lungs and air passages, designed to expel harmful substances from the respiratory tract. Common causes of coughing include infection of the respiratory tract (for example, bronchitis or pneumonia), inflammation of the airways caused by asthma, or exposure to certain irritant substances such as smoke or chemical fumes. Depending on their cause, coughs may be productive – that is, phlegm-producing – or they may be dry.

In most cases, coughing is a helpful reaction that assists the body in ridding itself of excess phlegm and substances that irritate the respiratory system; suppressing the cough may actually delay recovery. However, repeated bouts of coughing can be distressing, and may increase irritation of the air passages. In such cases, medication to ease the cough may be recommended.

There are two main groups of cough remedies, according to whether the cough is productive or dry.

PRODUCTIVE COUGHS

Mucolytics and expectorants are sometimes recommended for productive coughs when simple home remedies such as steam inhalation have failed to “loosen” the cough and make it easier to cough up phlegm. Mucolytics alter the consistency of the phlegm, making it less sticky and easier to cough up. These are often given by inhalation. However, there is little evidence that they are effective. Dornase alfa may be given to people who suffer from cystic fibrosis; the drug, given by inhalation via a nebulizer, is an enzyme that improves lung function by thinning the mucus. Expectorant drugs are taken by mouth to loosen a cough. There is some evidence that guaifenesin is effective but, overall, evidence of benefit is poor. Expectorants are included in many over-the-counter cough remedies.

DRY COUGHS

In dry coughs, no advantage is gained from promoting the expulsion of phlegm. Drugs used for dry coughs are given to suppress the coughing mechanism by calming the part of the brain that governs the coughing reflex. Antihistamines are often given for mild coughs, particularly in children. A demulcent, such as a simple linctus, can be used to soothe a dry, irritating cough. For persistent coughs, mild opioid drugs such as codeine may be prescribed (see also Analgesics). All cough suppressants have a generally sedating effect on the brain and nervous system and commonly cause drowsiness and other side effects.

SELECTING A COUGH MEDICATION

There is a bewildering variety of over-the-counter medications available for the treatment of coughs. Most preparations consist of a syrupy base to which active ingredients and flavourings are added. Many contain a number of different active ingredients, sometimes with contradictory effects: it is not uncommon to find an expectorant (for a productive cough) and a decongestant included in the same preparation.

It is important to select the correct type of medication for your cough to avoid the risk that you may make your condition worse. For example, using a cough suppressant for a productive cough may prevent you from getting rid of excess infected phlegm and may delay recovery. It is best to choose a preparation with a single active ingredient that is appropriate for your type of cough. Diabetics may need to select a sugar-free product. If you are in any doubt about which product to choose, ask your doctor or pharmacist for advice. Since there is a danger that use of over-the-counter cough remedies to alleviate symptoms may delay the diagnosis of a more serious underlying disorder, it is important to seek medical advice for any cough that persists for longer than a few days or if a cough is accompanied by additional symptoms such as fever or blood in the phlegm.

COLD CURES

Many preparations are available over the counter to treat different symptoms of the common cold. The main ingredient in most of these preparations is a mild analgesic, such as aspirin or paracetamol, accompanied by a decongestant, an antihistamine, and sometimes caffeine. In some cases, the dose of each added ingredient is too low to provide any benefit. There is no evidence to suggest that vitamin C speeds recovery. However, zinc supplements may be effective in shortening the duration of a cold.

While some people find these drugs help to relieve symptoms, over-the-counter cold cures do not alter the course of the illness. Most doctors recommend using a product with a single analgesic as the best way of alleviating symptoms. Other decongestants or antihistamines may be taken if needed, although antihistamines may cause sedation. These medicines are not harmless, and care should be taken to avoid overdose if different brands are used.

COMMON DRUGS

Expectorants Ammonium chloride, Guaifenesin

Mucolytics Carbocysteine, Dornase alfa, Mecysteine

Steam inhalation Eucalyptus, Menthol

Opioid cough suppressants Codeine, Dextromethorphan, Methadone, Pholcodine

Non-opioid cough suppressants Antihistamines