Antihistamines

In hayfever, the big advantage of antihistamines is that they treat the nose, the eyes, and the terrible itching which some sufferers get in the throat or ears. The only other treatments which help so many of the symptoms are steroid tablets or injections, and desensitising injections. Both of these other treatments have disadvantages not shared by antihistamines.

In hayfever the drawback of antihistamines is that they are not so effective for the blockage in the nose which troubles some people.

Asthma is helped only slightly by antihistamines; they are rarely used for asthma in Britain because there are so many better medicines for that.

So if we could just stop histamine from working, we would help allergies.

Well, we can!

Antihistamines do exactly this. They are chemicals which look enough like histamine to fool the cells of the body, but not enough like histamine to make the cells of the body do the nasty things which cause allergy symptoms. (In technical jargon, they 'block histamine receptors').

In other words, antihistamines stop histamine from working in the body.

But histamine is is not just involved in allergies. In fact it plays a vital role in the brain. What it does in the brain is to keep us attentive, alert, and awake.

So if we stopped all the histamine in the body from working, we would get rid of allergy troubles, but fall asleep, or at least become inattentive. This would make us dangerous drivers, bad students, and generally bad at all the daily tasks which need alertness.

That is exactly what happens if you take old antihistamines. They should not be used any more, except for special reasons, such as when the doctor wants to make you sleepy.

Fortunately newer antihistamines help allergies with little or no effect on your brain. How do they do this? It's very simple. Some medicines hardly get into the brain from the blood. This is a disadvantage with antibiotics for brain infections. But when research workers made antihistamines which hardly got into the brain it solved the problem of sleepiness and inattentiveness. So the new antihistamines are vastly better.

The latest antihistamines are amongst the safest medicines there are. But there are differences between them in side effects.

Older antihistamines are bad news unless you need help getting to sleep

There is no real doubt in the minds of researchers that older antihistamines can cause road accidents.

They also hinder learning, exam performance and skilled tasks.

Older antihistamines also had some other side effects which might in a few people cause difficulty passing water or increased pressure in the eyes (glaucoma), although this seems to have been rare.

There is now little reason to use the older antihistamines.

How do we know that the new antihistamines are better? There has been lots of research which shows this, but two experiments are specially interesting.

Road safety experiment

In one set of experiments, drivers had to drive along a motorway for 100 kilometres. They had to drive at a steady speed and keep as near to the middle of the slowest lane (the left hand lane, as it was in the Netherlands) as they could. A video camera on the roof of the car filmed the white line on the road. When they got back, the video tape was played, and the movement of the white line on the screen was measured.

In some tests the drivers took an old antihistamine, and in other tests they took a new one or a dummy tablet.

The old antihistamines made the drivers wobble more during driving, sometimes to a dangerous extent, so that the test drive had to be stopped. (They used dual control cars, and had permission to stop on the hard shoulder of the road when this happened.) Old antihistamines were frankly dangerous.

New antihistamines caused no increase in wobbling compared to the dummy tablets.

Alcohol, even within the legal limit for driving, also made steering more wobbly. But the new antihistamines together with alcohol were no worse than the alcohol alone.

So the new antihistamines are much safer for drivers.

Learning experiment in children with hayfever

Schoolchildren with hayfever were divided into three groups. For the experiment, during the hayfever season, children in the first group took dummy tablets. Those in the second group took an old antihistamine. Children in the third group took a new antihistamine, Triludan.

All the children then sat in front of computers. They used a computer program which taught them about farming in the Sahel Desert. As the children were from the town of Maastricht in the Netherlands, this meant they knew nothing about this at the beginning.

When the children had finished learning, they played a computer game. Guess what? The game was about - farming in the Sahel desert. Depending how well they did, each child got a score.

Here are the results. The children whose hayfever was treated with the old antihistamine did WORSE than the ones who just got dummy tablets. The sleepiness, or inattentiveness did more harm to how they did than hayfever alone.

But the children who took the new antihistamine, Triludan, did BETTER than the children who took dummy tablets. This shows that hayfever by itself harms learning, and that treating the hayfever undoes this harm, provided the treatment does not make the children sleepy.

Both sets of experiments were done by the team of Professor O'Hanlon, of Maastricht, Netherlands. If he'd let me use some photographs of these experiments, I would show them to you on the web.

Many other experimens have shown similar results.

So the new antihistamines are much better for schoolchildren, students, and people who need to use their brains, which means all of us.

• Older antihistamines, which cause sleepiness
• Newer antihistamines, which cause little or no sleepiness

Even preschool children should not have the older antihistamines in our opinion, again unless there is a specific reason why a doctor prescribes them in order to cause sedation or sleepiness. One reason for doing so is to reduce scratching in children with eczema.

The newer low-sedating antihistamines are at least as effective for hayfever and other conditions. They cost more, but are still on the whole reasonably priced.

Manufacturers can and do change the ingredients of non-prescription medicines without changing the brand name or informing the medical profession. No doubt they do so because they think you are more likely to part with your money on the basis of a known brand name than because you understand what is in the medication. Because of this, information on these drugs is especially likely to become inaccurate. Please let us know if you find errors.

All these are good. They differ in a number of ways, such as the size of the tablets, the length of time for which they act, how effective they are, the extent to which they may still have a slight tendency to cause sleepiness (though all are superior to old antihistamines for this) and in side effects and drug interactions as well as price. Your doctor should be able to recommend one. Fexofenadine (Telfast) is a development from terfenadine, its main advantage being an improvement in safety. In fact terfenadine is turned into fexofenadine in the body, so people have been exposed to fexofenadine since terfenadine was introduced about 15 years ago. However, fexofenadine, unlike terfenadine and some of the others, is not yet available without a prescription in the UK.

With so many antihistamines which mostly don't cause significant sleepiness, there is no good reason to take one which makes you sleepy unless you particularly want to be made sleepy. True, the older antihistamines are cheaper. But for most of the day it is important that you should have normal alertness. Drowsiness is a cause of accidents and impaired performance in work and study.

As sprays for the nose they are not as effective as steroid sprays , but some people prefer not to use a steroid, and your doctor may prefer to prescribe a drug which is not a steroid. If you think they may suit you, you could try them.

The newer antihistamine eye drops are more important because steroid drops do cause serious side effects sometimes and doctors rightly do not like to use the admittedly effective steroid eye drops. The antihistamine eye drops are similar to the so-called 'antiallergic' eye drops in effectiveness.

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