Sales of Sanofi's flagship diabetes drug Lantus slid almost 20% in the last quarter of 2015 as competition started to take its toll on the brand.
The emergence of biosimilar versions of the basal insulin product - as well as growth from other new drugs in the category such as Novo Nordisk's Tresiba (insulin degludec) and pricing pressure - impacted Lantus (insulin glargine) and contributed to an 11% dip in full-year 2015 sales to €6.39bn ($7.19bn).
Lantus was most affected in the US - with sales down more than 30% - offset slightly by the contribution from Sanofi's longer-acting Toujeo follow-up, which added $98m in the fourth quarter. Toujeo is still in the early stages of roll-out following its approval in the US last February and in the EU in April.
Sanofi chief executive Olivier Brandicourt said he was encouraged by the growth of Toujeo, pointing to sales acceleration in recent quarters "primarily driven by rapid market access in the US and fast adoption by prescribers".
Sanofi also reported a slump in fourth-quarter net income, down 75% to €334m, while group sales rose just over 2% to €9.3bn, buoyed by subsidiary Genzyme's portfolio of rare disease and specialty drugs, which grew 28% to €1.01bn in the fourth quarter, as well as vaccines which were up 15% to €1.44bn.
Sanofi has been anticipating the fallback in Lantus sales and last year implemented a cost-savings programme aimed at cutting €1.5bn off annual expenses through 2020, when it hopes new brands such as Toujeo, cholesterol-lowering therapy Praluent (alirocumab) and oral multiple sclerosis therapy Aubagio (teriflunomide) will step into the breach.
Praluent - which was approved in the US and Europe last year - added €5m to the firm's coffers in the fourth quarter.
While questions have been raised about how readily the drug will be used given its high price compared to rivals such as statins, Brandicourt said it now has reimbursement cover for "over 170m covered lives, about 72m of which is in either an exclusive or preferred position".
Meanwhile, Aubagio (approved in 2012) brought in €272m, an impressive 70% increase which suggests the drug is gaining ground in the oral MS space where it competes with Biogen's Tecfidera (dimethyl fumarate) and Novartis' Gilenya (fingolimod).
Sanofi also has great expectations for Dengvaxia - the first vaccine for dengue fever that has been approved so far in Mexico, the Philippines, Brazil and El Salvador.
The company recorded no sales for the new product in 2015 but indicated it had already shipped a million doses to the Philippines for the private market and is in discussion with the authorities on a three million-dose tender for the public market.
While not giving a prediction of 2016 sales, Brandicourt indicated that analysts' consensus sales estimates for the vaccine in the coming months of around €200m "make a lot of sense to us".