A pharmaceutical company stands accused of putting profit before patients after withdrawing a drug used in the treatment of a chronic debilitating disease – ahead of relaunching it at a price predicted to be up to 20 times higher.

Three of Britain's leading neurologists have written to the Health Secretary, Jeremy Hunt, to protest at Genzyme, part of the multinational drug company Sanofi, halting supplies of the drug alemtuzumab for multiple sclerosis.

The drug is currently licensed for the treatment of leukaemia. But it has been known for 20 years also to be effective in MS patients suffering from an aggressive form of the disease.

Neurologists have used the drug in these patients "off label" – prescribing it on their own initiative even though it was not licensed for multiple sclerosis – following encouraging results from a large placebo-controlled trial published in the New England Journal of Medicine in 1998. Alemtuzumab, which is given in two courses a year apart, costs markedly less than other drugs for multiple sclerosis to which it is thought to be superior – around £2,500.

Genzyme has now applied for a licence for the drug in multiple sclerosis to regulators in Europe and the US and is expected to relaunch it under the trade name, Lemtrada, at what could be many times its current price. In the meantime the company has withdrawn the drug from MS patients' off-label treatment, pending the granting of the licence, on the grounds that "any adverse event outside a clinical trial … may complicate the regulatory process".

In the neurologists' letter to the Health Secretary, professors Neil Scolding of the University of Bristol, Neil Robertson of the University Hospital of Wales and John Zajicek of the University of Plymouth say that Genzyme's decision has "serious implications for vulnerable UK patients with MS". They say patients who have already started treatment will "not be able to get their vital second course", and new patients may "miss their window of therapeutic opportunity" putting them at risk of "progressive, severe disability".

When licensed, they say, the drug's price is expected to be "15 to 20 times greater", and its withdrawal sets an "inappropriate precedent". They add: "It shows little regard for patients whose opportunity to alter the course of their disease is time-limited, and may represent an over-enthusiastic attempt by the parent company to profit from the current situation."

Professor Zajicek said he had personally treated about 150 patients with the drug, and 400 to 500 had received it across the UK. "Many of us think it is the best drug for patients with aggressive MS in the early stages of the disease. It's the greedy behaviour of the drug company that upsets me. They are just trying to rebrand it and put the price up. It is morally corrupt."

A spokesperson for Genzyme said: "Our goal is to ensure that Lemtrada is approved by regulatory authorities and made available to multiple sclerosis patients as quickly as possible. Until approved risk-management programmes are established, the use of Lemtrada for MS should occur only in clinical trials. Off-label use of alemtuzumab in MS has always been at the discretion of individual clinicians without reference to the company."

"In the UK, our price for Lemtrada and the value it brings to patients will be subject to the usual health economic evaluation by the National Institute for Health and Clinical Excellence."

Doug Brown, Head of Biomedical Research at the Multiple Sclerosis Society, said: "Alemtuzumab shows real promise as a potentially new medicine for many people with relapsing-remitting MS. There is no good reason why people with MS who have been allowed to benefit from the treatment should now be denied it.

"Genzyme need to come up with a scheme, quickly, that makes their product available to all those people currently being treated and, if it's licensed, price the drug reasonably so it is deemed cost effective on the NHS."

A Department of Health spokesperson said: "We know how important this drug is for some MS sufferers and are working closely with the company and the NHS to help make sure these patients can still access it."

Case study: 'I have seen the way my mother is suffering'

Oritse Williams, 25, of the platinum-selling boyband JLS, knows the suffering caused by multiple sclerosis since his mother, Sonia, 54, was diagnosed over a decade ago. He and his brother pledged when in their teens that they would do all they could to help her.

"We decided that when we grew up, my brother would become a scientist and I would try to make money from my music. That way we would have both the means and the ability to find a cure." Williams cared for his mother through his childhood and until he appeared in the final of The X Factor in 2008.

The drugs company: Sanofi

Sanofi, based in Paris, is the world's fourth-largest pharmaceutical company, employing 113,000 people worldwide.

Last year the company made a profit of almost €6bn on revenue of €33b. Its products include Clomid, for female infertility, the anti-clotting agent Plavix and the cancer drug Taxotere.

The company is the world's largest producer of vaccines through its subsidiary Sanofi Pasteur. It acquired Genzyme, a US biotech company based in Cambridge, Massachusetts, in 2011.

In 2010 Sanofi sacked 1,700 US employees citing growing competition from non-branded generic manufacturers. It denied the action was related to its purchase of Genzyme.