The parents of two teenagers dying from vCJD may learn today whether they have the go-ahead to try an experimental drug treatment.

If the legal moves are successful, the patients involved - a man of 18 and a 15-year-old girl, who cannot be named for legal reasons - are likely to become the first in the world to receive the drug injected directly into their brains.

Every day we lose, every hour we lose makes it harder for the drug to do its job

Father of 18-year-old vCJD patient

The case could revolutionise the way that the UK approaches fledgling therapies which might help terminally-ill patients.

The father of the 18-year-old told BBC News Online: "Every day we lose, every hour we lose makes it harder for the drug to do its job.

"If he has the treatment and it doesn't work, at least I know I have done everything I can to help him.

"My son would not only have wanted me to do what I'm doing now - he would have expected me do do what I'm doing now."

The parents have found doctors willing to carry out the treatment, but medical staff want court approval before delivering the drug, pentosan polysulphate - the effects of which are still less than certain when given this way.

The BMA would be concerned if there was a right to demand treatment as opposed to a right to ask for treatment

Dr Vivienne Nathanson, British Medical Association

Studies in animals have given some reassurance about safety and even boosted hopes that it might have an impact on the disease.

But some experts remain concerned that it may be harmful.

The judge in the case, Dame Elizabeth Butler Sloss, will have to decide whether it is ethically right for patients who cannot freely give consent themselves to be subjected to such an "unknown quantity" - even if there is a chance it may help them.

The hearing is in private, and although a provisional decision is likely to be given on Friday, this may not be made public for some weeks.

The hospital where the procedure would take place also cannot be named.

Experts on UK law and ethics say that it will prove a considerable dilemma for the judge.

Dr Vivienne Nathanson, from the British Medical Association (BMA), told the BBC: "The BMA would be concerned if there was a right to demand treatment as opposed to a right to ask for treatment"

Pentosan, the drug involved, is not a new medication - it has been used previously in patients with bladder and bowel inflammation, but it has no current pharmaceutical licence in this country.

vCJD is thought to be caused by "rogue" proteins called prions, which corrupt other proteins in the brain and form clumps which slowly kill brain cells.

At present there is no available treatment that can reverse or even slow down this decline.

Pentosan, it is hoped, may be able to latch onto prions, rendering them less harmful, and perhaps allowing them to be flushed out of brain cells.

Unknown quantity

The drug molecule has to be injected directly into the brain because it is too big to pass from the bloodstream across a protective filter called the "blood brain barrier".

What doctors are unsure about is how much pentosan would have to be given to have an impact on vCJD in the human brain, and how much it is safe to give.

Some studies have already suggested that it could have a role in patients who have been "infected" with vCJD prions, but have not yet developed clinical signs of the disease.

Statistical experts say that although the number of people who have so far developed vCJD, probably as a result of exposure to BSE infected meat during the 1980s and early 1990s, is currently only in the hundreds, the true numbers likely to go on to develop it are unknown, as it may incubate for decades in the body.

It is hoped that blood and perhaps even urine tests for the disease will become available soon, and there have been calls for mass testing of the population to assess the true extent of infection.