Spring Bank Pharmaceuticals (SBPH) said Wednesday it was abandoning efforts to develop a drug to treat hepatitis B as a result of “unexpected serious adverse events,” including a patient’s death in a mid-stage clinical trial.

“We are deeply saddened by the death of a patient in our Catalyst 2 trial,” Martin Driscoll, president and chief executive of Spring Bank, said of the clinical trial testing an experimental drug called inarigivir soproxil.