If you have multiple myeloma, your body is destroying bone faster than it is being replaced. This makes bones weak and painful and more likely to break. Darzalex 400mg Injection may be prescribed along with other cancer treatments such as chemotherapy. It is an important part of your treatment and increases the survival rate of people with multiple myeloma. This medicine will kill the cancerous cells and prevent their further growth as well as spread to other parts of the body. Follow your doctorâs instructions carefully to get the most benefit. Supplements of calcium and Vitamin D3 are also effective and may be prescribed if you do not have high blood calcium levels.