Hi thanks for contacting HCM... You are mentioning patient is HBSag positive .... If exposure is within 72 hour then anti gamma globulin antibody against HBSag can be taken which neutralize antigen... But after that preformed antibody not helpful.... No other antidote available... It is our immunity that eliminate virus.... To prevent infection from HBSag positive patient care taken not to come into contact with secretions from patient.... HBSag positive patients utensil clean with bleach solution.... Avoid sharing of objects with positive pateint to prevent infection.... Take care. Dr.Parth