Medication
This section covers:
Antihistamines
Adrenaline
- What form does adrenaline take?
- Who should be prescribed adrenaline?
- What is the dose?
- How many should be prescribed?
- Is adrenaline dangerous?
- Does adrenaline have any important drug interactions?
- Is adrenaline infallible?
More information and resources are available as par t of our AllergyWise training courses.
Antihistamines
Antihistamines are useful for controlling mild symptoms of allergy.
Cetirizine (known as Benadryl, Piriteze and Zirtek) and Loratadine (known as Clarityn) are two which may be recommended. Both are non-sedating antihistamines, meaning they are unlikely to make the patient feel drowsy. Chlorphenamine (Piriton) is an 'old school' antihistamine, which can make the patient sleepy, and shouldn’t be used by anyone driving or handling machinery.
For people at risk of anaphylaxis, antihistamines are usually prescribed alongside injectable adrenaline. They are intended for mild or early symptoms, but adrenaline should always be used when a severe allergic reaction is suspected.
Adrenaline
Adrenaline (also called epinephrine) is the recommended first line treatment for people with anaphylaxis.
The following notes are intended as general information only. Healthcare professionals should be guided by the medical literature. Links are provided at the foot of the page.
What form does adrenaline take?
Pre-loaded adrenaline injection kits – Anapen, EpiPen or Jext – are available on prescription for those thought to be at risk of a severe reaction. Please see the news section of our website for updates.
Anapen has a mechanism whereby, on pressing a firing button, a spring-activated plunger pushes the needle into the outer thigh muscle, delivering a single measured dose.
Distributor: Allergy Therapeutics plc, Dominion Way, Worthing, West Sussex BN14 8SA. Tel: 01903 844 700. www.anapen.co.uk
EpiPen has a spring-loaded concealed needle that delivers a single measured dose when the pen is jabbed against the muscle of the outer thigh.
Distributor: Meda Pharmaceuticals Ltd, Skyway House, Parsonage Road, Takeley, Bishop’s Stortford CM22 6PU. Tel 0845 460 0000. www.epipen.co.uk.
Jext is the most recent single-use adrenaline auto-injector to be made available. Jext has a locking needle shield which engages after use, designed to protect against needle stick injury.
Distributor: ALK-Abelló Ltd, 1 Manor Park, Manor Farm Road, Reading, Berkshire RG2 0NA. Tel: 0118 903 7940. www.jext.co.uk
Who should be prescribed adrenaline?
This has been a matter for heated debate among experts. Clearly adrenaline should be prescribed to anyone who has suffered a severe allergic reaction in the past. But some people who have had mild or moderate reactions in the past are also at risk of more severe ones in the future. Therefore it is often a matter of judgment in individual cases whether adrenaline should be prescribed.
Many leading allergy doctors believe it is reasonable to prescribe injectable adrenaline together with oral antihistamine for anyone who has had a previous allergic reaction where:
- There were severe symptoms, particularly if the patient felt faint or went unconscious
- There were breathing difficulties, even mild ones
- The reaction occurred to only a trace amount of allergen
- The patient has asthma as well as allergies, and the asthma requires regular treatment
Some doctors believe that adrenaline should be prescribed to anyone who is allergic to peanuts, tree nuts (such as walnuts, Brazils, cashews), seeds, fish or shellfish, even if reactions have been mild or moderate. In the end it will be up to the individual doctor.
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.
How is adrenaline administered?
EpiPen, Anapen and Jext are injected into the muscle in the outer thigh. Patients need to discuss this with their GP or allergist so they are clear on this point.
Guidance is given at www.epipen.co.uk, at www.anapen.co.uk. and at www.jext.co.uk
What is the dose?
The EpiPen and Jext deliver a 0.3mg dose in adults and children weighing over 30kg. Junior versions deliver a 0.15mg dose for people who weigh between 15kg and 30kg..
The Anapen is produced in three dosage strengths. Anapen 500 is approved for patients weighing 60kg and higher. Anapen 300 is recommended for people weighing 25kg and higher. Anapen Junior 150 is recommended for children weighing 15-25kg.
Children weighing less than 15kg may be prescribed an injector at the prescriber’s discretion.
How many should be prescribed?
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 (for example, home, school). Others advise there should be two devices in each location, in case one is broken or misfires, or a second injection is needed before emergency help arrives. This would be particularly important if the patient is going to a remote location where prompt medical attention is unavailable. Each individual patient must be guided by their GP or allergist.
Is adrenaline dangerous?
Used correctly, adrenaline injectors are safe for the vast majority of people who carry them. Used incorrectly (such as injected into the wrong place) there could be problems. Training and re-training are essential. Based on the current evidence, the benefit of using appropriate doses of adrenaline into the correct site (the muscle of the outer thigh) far exceeds the risk.
Does adrenaline have any important drug interactions?
Anaphylaxis may be made worse by Beta blockers and these drugs decrease the effectiveness of adrenaline. Other drugs may also be contra indicated.
Links for healthcare professionals:
Resusitation Council: Emergency Treatment Guidelines
Resusitation Council: FAQ's for healthcare providers
BMJ Clinical Review on Adrenaline
Journal of Asthma and Allergy Study
Is adrenaline infallible?
There is good evidence to show that adrenaline injectors, when used correctly, reverse the symptoms of a severe allergic reaction. However, adrenaline will be effective only if it is available at all times, is used correctly and is used promptly.
Early use of adrenaline leads to improved outcomes. Evidence in the medical literature suggests that a delay may lead to a poor outcome. This emphasises how important it is to obtain detailed guidance from a medical professional.
People who are overweight should be aware of the possibility that the needle may not reach the muscle. This does not necessarily mean there will be no beneficial effect. However this too needs careful discussion with a medical professional.
Note that adrenaline injectors have a use-by date. People who carry them should make sure they go to the doctor for a replacement before this date. There is some evidence that adrenaline that has recently passed its use-by date still has some effect, but this would be reduced.
