If the cream is only to be used for seven days, this is either because it could cause additonal problems is used longer, and/or it may be because after seven days the problem should be better, and at that point you should contact your doctor. In any event, if the boil doesn't improve beyond this point without the cream, I wouldn't use it any longer without first consulting a doctor, who may tell you to continue it, or may want to take a different approach to treatment.
I hope this is helpful. Best of luck to you.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist