Anaphylaxis: it can be more sting than a bee

3. June 2011
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The (early) summer is also the time of the flying pests. Insect bites are usually harmless, in individual cases however sometimes also dangerous. The lethality of an anaphylactic reaction is extremely high. The arsenal of pharmacological weapons employed is not always helpful.

Each year it is estimated that up to 250 people die of anaphylactic shock. Since anaphylaxis in many instances is not recognised and treated accordingly, one can even assume a significantly higher number of unreported cases. There is no precise data on it as yet since there are no reporting requirements in Germany. The Allergy Centre Charité in Berlin has put together a Registry System with the view that all possible anaphylactic reactions in all German-speaking countries be covered. According to the Head of the registry, Professor Margaret Worm, more than 60 allergy centers in Germany, Austria and Switzerland are participating in the data collection. The data is anonymous and can be decoded again later by the treating center. In addition, practicing allergists and family physicians can participate in the anaphylaxis reporting scheme. The data collection forms a basis for improvements in diagnosis, treatment and prevention of anaphylaxis and will ultimately improve patient care.

The most common triggers of anaphylaxis are – with almost 40 percent of cases – insect bites, of these almost 60 percent being from wasps. Triggers for an insect venom allergy in Germany are exclusively hymenopterans (ie.insects of the order Hymenopterae), especially honey bees, bumblebees, various species of wasps, among which is the hornet. The sting has arisen in the course of evolution from the ovipositor. So male hymenoptera apparently stinging ”only want to play“ – sting they cannot. Wasps have, compared to bees, shorter stilets and more powerful muscles. They can for that reason usually draw the sting out of the skin and repeat a sting. Wasps are short-sighted and therefore tend to approach very close to us. Blowing and waving of hands are interpreted as an attack and so they act to defend themselves. The venom includes biogenic amines, polypeptides, enzymes and kinins. The main part consists of histamine, adrenaline and acetylcholine. Serotonin and dopamine are also constituents, a sting doesn’t however leave us happy. “Three hornets can kill a man, seven can kill a horse”: this layman’s saying is wrong. In the instance of an allergy, one sting is fully sufficient.

Severe anaphylaxis is presented in the updated guideline on “Acute Treatment of Anaphylactic Reactions“ – put together by the German body of specialists on this topic – as the case when, in addition to skin symptoms, reactions such as vomiting, bronchospasm, cyanosis, shock (grade III) or even respiratory failure or cardiac arrest (grade IV) are involved.

Adrenaline and cooling of local reactions

Allergic reactions to bites from mosquitoes and horse-flies are rare. However, depending on the amount of poison, considerable swelling may occur at the injection site. Over-reactive allergy sufferers who are in a poor physical state on the day are in their reaction difficult to predict. There is always a residual risk. Bee or wasp stings in the throat should be treated immediately. A “cautious deferral” given to see whether the reaction gets worse can cost the patient his or her life. Especially in children, the trachea can swell up within minutes. Immediately call an emergency physician, cool the throat with ice from inside and outside. Where available, epinephrine should immediately be sprayed into the throat. Cortisone is helpful, but its effect has a time delay.

Antihistamines or calcium?

The effectiveness of oral antihistamines or even calcium in such an emergency is disputed. Calcium ions are involved in the liberation of histamine from mast cells. If the calcium channel is opened, allergenic histamine can escape from degenerated mast cells. If one wants to proceed in an anti-allergic manner, one should deprive the patient of calcium. Mast cell stabilisers such as sodium chromoglycate protect the mast cell from calcium overload. No calcium-containing medication lists in its technical information any allergic or anaphylactic reactions at all. Nutritional supplements also mention only a “recommendation of a calcium-rich diet” but shirk the matter on the word allergy. Its something to be regarded as advertising lyricism, when is shown on such preparations a sun. Unlike other countries, the use of calcium with allergy (prophylaxis) is in Germany widespread. There exist no evidence-based studies.

Second-generation antihistamines (loratadine, cetirizine) act as competitive antagonists and can only dock at the receptor when the histamine element is released. Histamine has the higher affinity. First-generation antihistamines such as dimetidine do not block the receptor, but switch the whole histamine-receptor complex to “inactive”. This happens rapidly and with high effectiveness, unfortunately this brings with it a strong sedative effect. This is with emergency patients not desirable.

Emergency kit is a must!

Frightening is the fact that only 3.4 percent of patients have an emergency kit including epinephrine. This includes allergy sufferers who have already reacted surprisingly strongly to a particular allergen and who are especially at risk for anaphylaxis. This group of patients especially benefits from an emergency kit, which should, in case of acute pain, always be quickly at hand. Risk patients should carry an emergency kit with them, in which at all times – according to the risk of allergy – an amount of adrenaline is included. Adrenaline can be injected by a layman with an appropriately dosed auto-injector. There are adrenaline products for self-injection, matched to the patients in different dosages. Doses suitable for children also exist. The emergency kit should also include an antihistamine, a cortisone, and (for asthma patients/ in case of shortness of breath) an asthma spray. All medications must be regularly checked for their expiration dates. Cortisone requires half to one hour before taking effect. The guideline recommends the immediate intra-muscular administration of 0.3 to 0.5 mg epinephrine (for children 0.1 mg/10 kg body weight) in the outer thigh. This therapy can be repeated if necessary – depending on the effect and adverse events – every 10 to 15 minutes.

It makes sense to conduct allergy tests at least three weeks after the allergic reaction, since the body’s entire stocks of IgE have been used. The corresponding blood test (RAST) can’t help either, because its mechanism centres on the presence of the antibody.

When one of our busy little honey bee friends do happen to give us the sting, local antihistamines and local anesthetics help, as does cooling the affected area. Essential oils such as tea tree or peppermint are not useful. After a subjective cooling, local hyperemia occurs, and so the tormenting itch becomes even stronger.

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