Plethora Solutions Holdings Chairman Bill Robinson is stepping down from his role at the pharmaceuticals company.Jim Mellon will take over as Chairman with immediate effect temporarily until a successor is found. Robinson, who has been Chairman since 2009, will remain a Non-Executive Director of the company until the next annual general meeting.The group also announced the resignation of Richard Horsman as Non-Executive Director who joined in 2011."We wish to thank both Bill and Richard for their service as directors, both of whom have contributed during a period of significant change and challenge to the company," said Mellon.RD