Investigators in Croatia have formally opened a probe against 76 people - including doctors and the management of a local pharmaceutical company - as part of an anti-corruption sweep.

The Balkan nation is required to fight corruption before it joins the European Union next year as the bloc's 28th state.

The anti-graft police said Wednesday that nine people will be kept in detention during the investigation into allegations that the local pharmaceutical firm Farmal had bribed doctors into using its products.

Police say Farmal gave money and gifts or organized trips for the doctors over the past three years in return for them prescribing its medicines. The group being investigated includes 49 doctors, a pharmacist and 26 pharmaceutical company employees.