Interferon beta is available in the UK, but some health authorities have controversially refused to fund it on the grounds that it is too expensive, or its worth has not been proven.

The treatment costs about £10,000 per patient per year.

The studies, reported in the medical journal The Lancet, looked at different forms of the drug, and their impact on different forms of the disease.

One study found that interferon beta 1a can slow the progression of the relapsing-remitting form of multiple sclerosis and reduce the frequency of relapses.

The second found that interferon beta 1b was an effective treatment in the secondary progressive form of the disease.

More than 500 patients worldwide with relapsing-remitting multiple sclerosis took part in the two-year interferon beta 1a study.

The researchers found that the drug:

• Reduced the frequency of relapses

• Slowed the rate of disability

• Minimised damage to brain tissue

The patients, two-thirds of whom were women, were split into three groups.

They were then given injections of either high dose interferon beta (44 micrograms), low dose (22 micrograms) or a placebo, three times a week for two years.

All patients were kept under close medical supervision, which included neurological examinations every three months and a magnetic resonance scan every six months.

The number of relapses was reduced by 27% in the low dose and 33% in the high-dose group. Better still, this reduction included mainly the serious relapses.

Twice as many patients who took the high dose (45%) were free of any relapse after one year of treatment compared with patients who took a placebo.

Successful results

The researchers also found that the progression of disability slowed by 75% in patients taking the high dose compared with placebo patients.

Scans obtained by magnetic resonance imaging (MRI) showed that more than three-quarters of brain lesions had ceased to grow in patients treated with high-dose interferon beta1a.

Side-effects such as flu-like symptoms, muscular soreness and irritations at the injection sites were more frequent among those treated with interferon than in the placebo group.

However, only five patients had to stop the treatment because of side-effects.

Dr Andrew Galazka, Senior Vice-President for Medical Affairs at The Ares-Serono Group, said: "This is the most comprehensive study of any therapeutic agent in relapsing-remitting multiple sclerosis undertaken to date and shows, for the first time, significant improvement in all major outcome measures."

In the second study, by the European Study Group, 718 patients with secondary progressive MS were randomly allocated interferon beta 1b or a placebo for up to three years.

The researchers found that "there was a highly significant difference in time to confirmed progression of disability in favour of interferon beta 1b".

'Make the drug available'

The NHS Executive has licenced the use of both interferon beta 1a and beta 1b for the treatment of relapsing-remitting multiple sclerosis, provided it is prescribed by a neurologist.

However, some health authorities have chosen to ignore the guidelines.

A spokesman for the Multiple Sclerosis Society of Great Britain and Northern Ireland said the mounting evidence that the inferon betas were effective made it imperative that health authorities sanctioned their use.

He said: "It is totally unacceptable to have a situation where somebody living on one side of a parish is prescribed interferon while somebody living not far away with exactly the same condition is not - that makes a complete mockery of the NHS."

Immune system attacks itself

Drugs lead to less brain damage

Nobody knows exactly how interferon beta works. Nevertheless, when present in the body in sufficient quantities, it reduces the output of another chemical called interferon gamma, that is known to stimulate the destructive activity of the immune system.

In multiple sclerosis patients interferon gamma causes the immune system wrongly to identify body cells are foreign invaders.

As a result, the myelin sheath coating nerves in the brain and spinal cord is destroyed by mistake.

As a consequence, transmission between nerve cells slows down and becomes irregular, leading to loss of balance, reduced vision and bouts of localised paralysis.

Eventually, patients may become totally paralysed and wheelchair-bound.

According to the World Health Organisation, multiple sclerosis affects about 2.5m people individuals worldwide, of which about 1% die each year.

Relapsing-remitting MS patients initially experience one or more bouts of illness, followed by complete or partial recovery. Patients are clinically stable between relapses.

Progressive MS patients become gradually more disabled.

Secondary-progressive MS patients start out with the relapsing-remitting form of the disease, but then experience gradual progression of disability.