Swiss pharmaceutical giant Novartis has replaced the top managers at its Japanese unit after a third-party probe found employees had acted questionably in clinical trials on a leukaemia treatment.

The probe's findings included possible destruction of evidence and the potential obtaining of patients' personal data by employees of the Japanese unit.

Novartis said there was a possibility the investigation, which was commissioned by the company and is scheduled to be complete by summer, could uncover problems with other doctor-led clinical research.

David Epstein, head of Novartis Pharmaceuticals, said the actions of the employees violated the company's ethical standards and acknowledged a need to rebuild the Japanese unit under the new management team.

Dirk Kosche, previously head of emerging growth markets for Novartis Oncology, will become head of the Japanese unit, Novartis Pharma, replacingYoshiyasu Ninomiya, who was appointed head of the unit last year. Michael Ferris, an adviser to Novartis Pharmaceuticals, will become president of Novartis Holding Japan.

The Japanese unit is also the subject of an investigation into alleged use of manipulated data to promote the drugmaker's best-selling blood pressure drug Diovan, which resulted in the filing of a criminal complaint against the company by the health ministry in January.