Ypsomed has filed the lawsuit in Germany and is seeking a ban on the manufacture and supply of the insulin pen, believing the SoloStar injection system is in breach of two European patents owned by Ypsomed group member company TecPharma Licensing AG.
The latest legal action follows last month's patent infringement claim by Novo Nordisk against the French drug giant's SoloStar pen in the US and Germany.
The disposable pen is for use with the company's 24-hour basal insulin Lantus (insulin glargine) and Apidra (insulin glulisine).
Novo Nordisk's allegations pertain to the mechanisms for injection and dose-setting, features which Sanofi emphasises as advantages of its product but which Novo claims infringe on its NovoPen 4 insulin delivery system.
The Ypsomed lawsuit, based on formal opinions from a number of specialist patent attorney offices, relates to alleged breaches of European patents EP 1414507 B1 and EP 1458440 B1, which relate to the technical working of the parts inside the pen.
Ypsomed president of the board of directors Dr Willy Michel said in a statement: "The business policy of Ypsomed is to protect its developments and technologies by patents and to defend them actively if needed.
As a partner for over 20 years, Ypsomed informed Sanofi-Aventis at an early stage of the patent breaches in connection with the SoloStar pen, negotiations have not as yet led to an acceptable outcome.
As a consequence Ypsomed has now decided to take legal action."
When contacted by in-PharmaTechnologist.com, Sanofi-Aventis spokesman Jean-Marc Podvin said the company's understanding of the allegations was preliminary.
He declined to comment further except to say "we do respect the legal patent rights of third parties."
He added : "It's our policy to vigorously defend our rights to provide access of products to our patients."
The Swiss company currently has long-term supply contracts with Sanofi-Aventis for the established pen systems OptiSet, OptiClik and OptiPen.
Ypsomed chief executive Richard Fritschi said in a statement he was confident Sanofi-Aventis would remain an "important customer".
Meanwhile, Podvin said he "would not speculate on how the contract relationship will evolve".
The SoloStar pen is the only pre-filled disposable insulin pen that allows patients to administer from one up to 80 units in single-unit increments with a single injection.
The pen offers a 25 per cent higher capacity than other insulin pens, according to the company, capable of holding 300 units of insulin.
The average Lantus dose is 35 units a day.
Sanofi also highlights the reduced injection force used with its SoloStar product, with the pressure required to administer the insulin 31 per cent less than Novo's FlexPen device and 54 per cent less than Eli Lilly's Humulin/Humalog pen.
Lantus is currently the only 24-hour insulin approved exclusively for once-daily treatment of hyperglycaemia in patients with Type I or Type II diabetes .
It is released into the bloodstream at a relatively constant rate throughout the day, eliminating the problem of the 'peak-of-action' effect common with other insulins, where the insulin reaches a point of maximum effect in the body.
Apidra is a new, rapid-acting insulin analogue for adult patients with type 1 and type 2 diabetes for the control of hyperglycaemia.
It offers patients mealtime dosing flexibility and can be taken within 15 minutes before or after starting a meal.
French and German launch of SoloStar was in April with US approval for the product also occurring in the same month.
Ypsomed possesses many patents in the area of self-injection devices, pen systems and auto-injector technology.
In May the company announced it had granted non exclusive license rights in patents relating to auto-injectors to a major but undisclosed pharmaceutical company.