In some cases there can be a secondary (biphasic) reaction. The time of occurrence of the second response can be anywhere from one hour to 72 hours after successful treatment and resolution of the initial response. Biphasic reactions can range from mild, not requiring further therapy, to potentially fatal symptoms. Clearly patients need to be observed for some time after initial symptoms have resolved (e.g. five hours) and should then be equipped with an appropriate rescue treatment and warned that a secondary reaction is a possibility.

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Assessing the risk

In 1994 the Chief Medical Officer said: “All patients suspected to suffer from peanut allergy should be referred to a specialist clinic. Even if the diagnosis is in doubt, patients should on no account be advised to test their reaction by eating peanuts.”

Since peanuts are by no means the only allergens capable of triggering life-threatening symptoms, a careful judgement is required in all cases to determine who should be referred. The ideal is for all allergy patients to be seen by a specialist at least once. A referral is particularly important if the allergy patient has co-existing asthma, as this may be a risk factor for a severe reaction.

The specialist should undertake a full assessment and may offer skin prick tests and blood tests. The patient should be provided with a management plan tailored to their specific case.

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Locating an allergy clinic

For a list of NHS allergy clinics, visit the website of the British Society for Allergy and Clinical Immunology: www.bsaci.org

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Treatments

Adrenaline (epinephrine) is the emergency treatment for a severe reaction. Given promptly, adrenaline can reverse features of anaphylaxis by acting on adrenoceptors. As an alpha-receptor agonist, it reverses vasodilatation and reduces oedema. As a beta-receptor, it dilates the airways, increases the force of myocardial contraction, and suppresses further histamine and leukotriene release.

There are two alternative injection kits prescribed to patients – the EpiPen and the Anapen. Each carries a single, measured dose of adrenaline, which is injected intra-muscularly.

The EpiPen has a spring-loaded concealed needle that delivers the dose when the pen is jabbed against the outer thigh. It is available as EpiPen, which delivers a 0.3mg dose, and EpiPen Junior, which delivers a 0.15mg dose. Both are also available in twin packs that contain two injectors.

Distributor: ALK Abelló, 2 Tealgate, Hungerford, Berks RG17 0YT. Tel 01488 686016. Website: www.epipen.co.uk

The Anapen has a mechanism whereby, on pressing a firing button, a spring-activated plunger pushes the needle into the thigh muscle. There are two preparations: Anapen, which delivers 0.3mg of adrenaline, and Anapen Junior, which delivers 0.15mg.

Distributor: Lincoln Medical, 13 Boathouse Meadow Business Park, Cherry Orchard Lane, Salisbury SP2 7LD. Tel 01722 410443. Website: www.anapen.com.

Both companies sell “trainer” pens for teaching purposes.

Unwanted effects are rare when appropriate doses of adrenaline are given by I.M. injection. However, the doctor should consider all co-existing medical conditions and check for potential interactions. For example, beta blockers and ACE inhibitors may hinder treatment.

The Junior version of each device is recommended for children weighing 15-30kg, although doctors may use their judgement and prescribe it for children weighing under 15kg. At 30kg, the child would normally then be prescribed the adult version. However, some doctors prescribe the adult version for children weighing between 20-30kg if the individual case warrants it (e.g. if the child is prone to reactions that are particularly severe).

Patients should be instructed to use their Salbutomol or Terbutaline inhaler if asthma is a feature of the reaction.

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Who needs adrenaline?

Allergic reactions vary in severity. On limited evidence, it would seem reasonable to prescribe injectable adrenaline together with oral antihistamine for anyone who has had an allergic reaction that:

• Was severe (laryngeal oedema, respiratory or hypotensive symptoms);

• Or was associated with respiratory symptoms (even mild);

• Or occurred on exposure to only a trace amount of allergen;

• Or occurred in someone who has asthma that requires regular inhaled corticosteroid therapy.

The decision to prescribe adrenaline should be part of an approach that includes a thorough assessment of the patient. This can best be done at a specialist allergy clinic or by a GP who has had training in allergy management.

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When and how to use adrenaline

The varied and unpredictable course of severe allergic reactions makes it difficult to define when adrenaline is best administered. The UK Resuscitation Council recommends giving adrenaline as soon as there is stridor, respiratory distress, wheeze or clinical signs or shock. Urgent transfer to hospital is vital.

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How many devices to prescribe

There is no consensus among experts about how many devices to prescribe for each person. Some advise that patients should have one device at each site that they regularly attend (e.g. home, school). Others advise there should be two devices in each location, in case one is broken or misfires. However regular training and re-training should help avoid problems. A second dose is unlikely to be needed if it is given early enough, but there might be occasions when it might be wise to have two devices available: for example, if the patient is going to a remote location where prompt medical attention is unavailable.

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An allergy management plan

There is evidence that the risks are reduced if the patient receives expert advice and assessment in a specialist allergy clinic and participates in a management plan. Where this happens, fewer patients have further reactions and when these do occur, they are mostly mild. Importantly, the patient should be educated on measures to avoid the allergen in the future. Families and carers, including school staff, must be competent to recognise when an allergic reaction has started and how to administer adrenaline. Follow-up is important to ensure regular re-training and assessment of allergy status.

As stated above, the presence of asthma in a patient with allergy must be considered a significant risk factor, and the patient must be encouraged, with plenty of helpful guidance, to keep the asthma well controlled.

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Outgrowing allergy

Common food allergies such as those to milk and egg are frequently outgrown. Peanut allergy is often lifelong. Up to 20 per cent of young children with peanut allergy outgrow it by the age of around five or six. Such children tend to be pre-school age and will probably have fewer other allergies or asthma than children whose peanut allergy persists. A challenge test may be considered if a child has an accidental exposure without having a reaction; or if a child’s last reaction was 3-4 years ago. This must be undertaken in hospital.

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