The French drug maker – who this summer inked a $20.1bn (€14.6bn) takeover deal – has recently reduced shipments of Genzyme’s Gaucher treatment, Cerezyme.
And last month the manufacturers also held up already rationed shipments of their Fabrazyme drug, used to treat Fabry disease.
The set backs meant that, in July, Sanofi failed to make a milestone payment to Genzyme investors.
Genzyme attribute the disruptions to a 2009 incident in which a virus was found in a bioreactor at its Allston Landing, US, facility and the company was forced to suspend production.
A spokesperson from Sanofi said: “We sincerely regret any disruptions to treatment plans, and we are working through local channels to inform physicians about how patients may be affected.
“Given current improvements to productivity and progress with our manufacturing recovery, we do anticipate an improving Cerezyme supply outlook from February 2012 forward.“
However Sanofi CEO Chris Viehbacher recently told Reuter’s that he expects Genzyme's manufacturing troubles to be largely resolved next year when its new plant in Framingham, US, opens.
He was also enthusiastic about Genzyme’s experimental multiple sclerosis drug Lemtrada, which is expected to produce critical Phase III results this year, after reducing MS relapses by 60 per cent in Phase II.
He said: "The company is nicely balanced, so I don't particularly see any reason to go out and do big deals, so that's completely off our radar screen."