Science: What's your poison?

Anything from stripping old paint to a dose of Chinese medicine can prompt a call to the National Poisons unit. Roger Dobson reports from the life-saving telephone service

IT IS nearly midnight when the call comes through.

An 18-month-old baby has been found by her parents playing with tablets, sitting on the carpet sucking the sugar-coated pills. She has swallowed some, although no one knows how many.

At first she seemed unaffected, but now, several hours later, she's started to vomit. On arrival at the local hospital's casualty department she is limp and pale and is retching violently and frequently. Her blood pressure is dropping fast and her white blood cell count is already down.

Doctors discover that the pills (now showing up on her stomach X-ray) contain ferrous sulphate, an essential nutrient prescribed to the mother during her pregnancy. Concerned about the baby's symptoms, they make an emergency call to the National Poison Information Service at Guy's Hospital. It is the 505th call of the day for the world's busiest poisons information centre, which fields requests like this from across Britain.

The centre, part of Guy's Medical Toxicology Unit with a staff of 65, is responding to record numbers of requests for help from doctors, nurses and the emergency services. In the last 12 months alone there have been 200,575 calls (all from professionals because only they can use the 24- hour service though a system of confidential telephone numbers). This increase is due partly to the unit's success, which has led to more doctors ringing in for a quick solution, and partly to the huge and growing number of potential poisons out there.

As consultant medical toxicologist Dr Virginia Murray points out, there are more than 4,000 therapeutic drugs alone to suffer dangerous side-effects from. Then there are the 70,000 or so products that are transported around the country which may be spilled and then inhaled, handled or eaten with serious consequences. A further 150,000 potentially toxic compounds are used by industry, all capable of causing health problems, and on top of that is a host of illegal "recreational" drugs, health supplements, alternative health remedies (which can contain toxic heavy metals), and the wide range of poisonous mushrooms and other wild plants.

If patients become ill when any one of these materials is eaten, drunk, sniffed, rubbed or even touched, it is the NPIS to which doctors turn.

"Our job is to give specific advice, whether the emergency involves a drug, fumes from a fire, an explosion, food contamination, land pollution or whatever. It involves not just what has been taken, but how much and by whom, and whether it is a multiple or a single exposure," says Dr Murray.

"We have to deal with literally anything. We have advised on the treatment of people who've been exposed to CS gas or sheep dip, and we've helped in cases where people have suffered lead poisoning from blow-torching old paint. At this time of year we get lots of calls about children who have eaten wild berries and mushrooms."

Pharmaceuticals make up the single biggest group of compounds that the NPIS advises on. Second on the list is household products, followed by drugs of abuse, occupational exposures, plants and fungi, and environmental toxins.

To advise doctors best, the NPIS draws on extensive data on substances and their potential toxicity to humans. This information comes from a variety of sources - from their own case histories, from product manufacturers, from the work of other specialist and academic centres around the world. Data on most toxic substances is kept in-house.

As well as acting as a reference centre the unit, which houses the NHS's largest toxicology laboratory, also analyses biological specimens using an array of mass spectrometers, gas chromatography and atomic absorption equipment. Mass spectrometry, for example, helps to produce a chemical "fingerprint" of the compound in question.

"If someone is exposed to a substance, it isn't sufficient simply to look that up. The body will metabolise it, and make it potentially more toxic, so we need to look for those resulting products and not just the raw substance," says Dr Murray.

As well as responding to requests for substances to be analysed, the unit carries out its own investigations, particularly where more than one similar case has been reported, as this may be the first clue to a major health problem. In that way, the centre acts as the first line of defence when new toxic dangers are beginning to emerge.

One of the NPIS's biggest recent investigations has been into the risks thrown up by the expanding "alternative" medicines market. Many of these products include substances new to Europe and can contain such toxins as arsenic and mercury.

More than 100 cases of poisoning have now been linked to the use of Chinese and other traditional remedies. Serious liver damage is among the side- effects blamed on their use and there has been at least one death in the UK. Doctors have been alerted to the potential dangers of herbal products which can cause damage to the central nervous system, paralysis, comas and convulsions.

The NPIS is now working with the Royal Botanical Gardens at Kew on founding an authentication centre for Chinese herbal medicines so that compounds can be identified, catalogued and matched against recommended treatments.

In its front-line role, the unit is regularly faced with life-and-death crises, where the speed and accuracy with which it can find out what is likely to happen to the patient and come up with a antidote is critical - particularly where children and babies are concerned.

In the operations room, it is now the early hours of the next day and the doctors looking after the ferrous sulphate baby are on the telephone again. This time it's good news - she has responded well to the treatment that they suggested and is conscious again, and the other piece of good news is there is also no sign of the feared liver damage.

In two days' time, the healthy baby will be discharged from hospital, thanks to the specialists who prescribed the right treatment in the middle of the night for a child they have never seen. !