"The terrible equation"

The temporary ban on NHS prescriptions of the anti-impotence drug Viagra indicates the government is more willing to discuss openly the issue of rationing.

Rationing has long been a taboo word for politicians.

It has never been easy to admit that the NHS cannot afford to provide every treatment for everyone who wants it.

But a health service with a limited budget faces hard choices when confronted by expensive treatments of variable effectiveness.

Affordable treatments

One of the most controversial rows over rationing concerns beta interferon, a treatment for multiple sclerosis.

The cost of beta interferon has proved controversial

The full effectiveness of the drug has yet to be established, and because it is very costly - approximately £10,000 per patient per year - some health authorities are reluctant to allow doctors to prescribe it.

As medicine continues to advance, more treatments are developed for previously incurable conditions.

Often these are expensive, and health authorities have to balance the financial costs versus the clinical gains.

Cancer drug

One recent example is a drug used in the treatment of ovarian cancer, Taxol, which has been licensed for use in the UK for several months

It costs £1,500 per injection and the average course requires six of these.

There are two studies that show the drug extends a patient's life by a year, but this is not enough evidence to justify prescribing it for everyone with ovarian cancer.

Marilyn Bush had the disease but was able to get the treatment because her private health care insurance agreed to pay for it.

She said: "Could you imagine how you would feel if you knew you could not possibly find the money for a drug you needed?"

She said her "heart went out" to patients who needed Taxol but were unable to get it on the NHS.

Health authority guidelines

Dr Gordon Rustin, who treated Ms Bush, said: "Some health authorities allow us to treat a few patients if we ask specifically and give all the clinical details for the patient.

"Some health authorities have made special funding available just for patients who fit into certain clinical trials and some health authorities have said they will not provide any extra funding for Taxol."

Dr Rustin said that before he sees a patient he has to check their postcode to see which health authority pays for their treatment. He says he can only then prescribe the drug if he knows the authority will fund it.

Hard choices

He said health authorities have to make a crude calculation.

"They want to show that we can improve duration of life with a new drug and they then try to calculate the extra duration of life," he said.

"If you get an extra year of life for less than £10,000 then it is generally considered that that is a reasonable buy."

Because longevity is so important in the authorities' calculations, he said, it was difficult to get funding for drugs that simply improve the quality of life.

Ms Bush said: "If you are reasonably comfortable then maybe you will want to go and get a bank loan to do it or use savings to do it, but it is wrong.