An advance warning system for allergies

October 22, 1999

Southampton has set up a unit to tackle allergies triggered by medical drugs. Geoff Watts reports

Allergy is one of nature's little teases: unpredictable, unproductive and, with strawberries and shellfish among its apparently arbitrary range of trigger factors, a biological conundrum. And it is not always so little, either; a minority of allergic reactions are life-threatening.

Most embarrassingly in this increasingly risk-averse society, medical drugs are on the list of potential allergens. Up to 1 per cent of people given certain antibiotics, for example, may suffer an allergic reaction. Anaesthetics can also be risky, partly because they are often given intravenously: "Mainlining into the danger zone", as John Norman, emeritus professor of anaesthetics at Southampton Medical School, puts it.

A research unit has been set up at Southampton to tackle the problem. The ideal solution would be to develop a simple blood test for revealing in advance how an individual would respond to any particular drug. Andrew Walls, senior lecturer in immuno-

pharmacology, admits that for economic and other reasons, such a thing is not yet on the agenda; but with a Pounds 100,000 grant from the Sir Jules Thorn Charitable Trust, he is aiming to improve matters.

Among the key players in allergic reactions are the mast cells of the body's immune defence system. These are packed with granules containing a cocktail of powerful chemicals, the best known of which is histamine. During an allergic reaction, the mast cells liberate these chemicals into the bloodstream. The greater the quantity released, the greater the response, says Dr Walls. "Some reactions can be quite mild - flushing or a skin rash. Or they can lead, within a few minutes, to cardiovascular collapse, respiratory collapse, brain damage and even death."

Anaphylactic shock, as the most severe reaction is called, requires swift action in the form of an injection of adrenaline. If the victim is not already in hospital, survival prospects are poor.

Diagnosing anaphylaxis is not always straightforward, even after death. Dr Walls asks his colleagues to send him a blood sample from any patient who is even suspected to have suffered an allergic reaction to a drug. He is developing an assay for an enzyme, tryptase, which is found only in mast cells and shows up in the circulation when they disintegrate. "Other mast cell products such as histamine have been looked at for some time, but they tend to degrade too rapidly to do a blood test. With tryptase you have two or three hours," he says.

It is important for clinicians to know whether or not an allergic reaction has occurred. Each year about one in 20 of the population receives an anaesthetic, says Professor Norman. "Give a particular agent to someone once and it may cause a slight reaction; give it to them a second time and you may kill them."

People often get a mixture of drugs, so even when the suspicions of an allergic reaction have been confirmed, the doctor may have to do a skin-test to reveal the culprit. The patient and the GP can then be warned, and any medical notes tagged accordingly.

"Inhibitors of tryptase or other substances causing the reaction could well be beneficial as treatments," says Dr Walls.

"But that's in the long term." So, too, is the ideal outcome: an economically practicable way of testing individuals in advance. But with the pace of biotechnology, "long term" is an ever-shortening period.

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