Sanofi-Aventis is the world's third largest drugmaker

The move will strengthen Sanofi's presence in eastern Europe.

It bought the stake from private equity firm Warburg Pincus and several Zentiva managers and staff.

Zentiva has operations in Romania, the Czech Republic and Slovakia, and is expanding into Poland, Russia, and the Baltic states.

Geographical fit

The Czech firm made a 65m euros net profit last year on sales of 410m euros, and has more than 4,000 staff.

Strasbourg-based Sanofi-Aventis is the world's third largest drugmaker behind Pfizer and GlaxoSmithKline.

"The geographical reach is interesting, because it is still a developing market in which Zentiva has a very good position," said Bank Sal Oppenheim analyst Peter Duellmann.

"At some point in time it makes sense to be able to offer a bundling of products [combining branded and generic drugs] and to have a foot in the door to sell generic drugs."