Sanofi has started to withdraw Campath/MabCampath from US and EU markets in order to prevent off-label prescribing of the cancer drug in multiple sclerosis (MS).
Campath (alemtuzumab) is used in the second-line treatment of B-cell chronic lymphocytic leukaemia (B-CLL) and is marketed by Genzyme, taken over by Sanofi in a $20bn deal last year.
Sales of alemtuzumab as a cancer treatment have been on the slide for some years, however, and the Campath brand brought in just $76m in 2011.
Sanofi sees a huge opportunity for alemtuzumab as a drug for MS - a product it calls Lemtrada - with Genzyme executives suggesting ahead of the takeover that this this could be a $3bn product.
The problem for the company is that the dose of alemtuzumab used in Campath therapy is much higher than for Lemtrada. That means if the cost of the treatment were kept proportional Sanofi would have to sell its MS product some distance below its competitors in the marketplace, such as Biogen Idec's Tysabri (natalizumab) and Novartis' recently-introduced oral MS drug Gilenya (fingolimod) which sell for around $50,000 a year.
On a dose for dose comparison, Lemtrada would sell for a $6,000-$7,000 a year. If Sanofi kept the prices comparable to its competitors there would likely be rampant off-label prescribing of Campath for MS, undermining the new brand, according to a BioCentury report.
B-CLL patients will not be affected by the move because Genzyme says it will continue to make Campath available - for free - via patient access programmes in most markets.
Genzyme filed Lemtrada for approval in June on the back of two phase III studies indicating its drug was superior to high-dose treatment with Merck Serono's Rebif (interferon beta-1a) on clinical and imaging endpoints, including a reduction in relapse rate.
The company also says some patients with pre-existing disability treated with Lemtrada in an earlier phase II trial were more than twice as likely to experience a sustained reduction in disability over two years than patients treated with Rebif.
Genzyme acquired worldwide rights to alemtuzumab from Bayer in 2009, in a deal which gives the latter an option to co-promote the product for MS.
Meanwhile, Genzyme's clinical development programme for relapsing multiple sclerosis includes the once-daily oral treatment, Aubagio (teriflunomide). This is currently under review in the US and EU but has so far failed to outperform Rebif.