Darzalex (Daratumumab): What It Is and What to Expect

Daratumumab is an antibody aimed at CD38, a marker myeloma cells carry in large amounts. Once it attaches, the immune system is recruited to destroy the cell.

It comes in two forms, and the difference is worth knowing. Darzalex goes into a vein, and the quantity is worked out from your body weight by the pharmacy each time. Darzalex Faspro is injected under the skin over a few minutes; it mixes daratumumab with an enzyme that lets a larger volume spread into the tissue, and it uses a fixed dose. They are separate products with separate labels, and their approved uses are not identical.

CD38 sits on red blood cells too, in small amounts. That confuses the cross-match test blood banks use before a transfusion. The antibody makes the test look positive even when your blood is fine, and it can carry on doing so for months after the last dose.

The fix is simple as long as people know. Type and screen your blood before treatment starts. Then tell any hospital, and carry a card saying you are on daratumumab. Without that, an urgent transfusion can be delayed while the lab works out what is happening.

Daratumumab can also confuse the blood and urine tests used to measure myeloma, because the drug itself is an antibody and shows up on the same tests. Your team knows to allow for that.

The intravenous label covers multiple myeloma only, in seven situations. Some are for people newly diagnosed, split by whether a stem cell transplant is planned. Others are for myeloma that has come back or stopped responding, after one, two or three earlier lines of treatment. It is nearly always paired with other drugs such as lenalidomide, bortezomib, pomalidomide, carfilzomib or dexamethasone. One use is on its own, after at least three prior lines.

The under-the-skin product covers more ground. As well as myeloma, it is approved on its own for high-risk smoldering myeloma, and with bortezomib, cyclophosphamide and dexamethasone for newly diagnosed light chain amyloidosis. The label warns it is not for amyloidosis with the most severe heart involvement outside a trial.

Reactions are common, especially with the first dose. They tend to bring a stuffy or runny nose, cough, throat tightness, wheeze, chills or nausea. Medicines are given beforehand to reduce them, and you may be sent home with steroids to take the next day. Some reactions arrive hours later, so tell the team about anything that starts after you leave.

White cells and platelets can drop, and infections including pneumonia and shingles are reported. Antiviral tablets are often prescribed to prevent shingles. Vaccination is usually planned around treatment. A fever of 38C or higher is an emergency on this treatment: ring the 24-hour number at once, at any hour, and go to an emergency department if nobody answers quickly.

• Call 911 or go to an emergency department if your throat tightens, your tongue or lips swell, or you wheeze and struggle to breathe after a dose, even hours after you got home. Tell the crew you are on daratumumab.
• Ring the 24-hour myeloma line that same hour if your temperature reaches 100.4°F (38°C) or higher, or chills leave you shaking; if you cannot get through, go to an emergency department and say you are on daratumumab. On treatment that drops white cells, a fever is a medical emergency and needs antibiotics fast, so it is not something to sit on overnight (CDC).
• Call your care team the same day if a painful band of blisters appears on one side of your body.
• Call your care team within a day or two if a stuffy nose, cough or chest tightness lingers after a dose, or if you notice new bruises, nosebleeds or bleeding gums.

https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a4d0efe9-5e54-467e-9eb4-56fa7d53b60b

https://www.cancer.gov/about-cancer/treatment/drugs/daratumumab

https://www.cdc.gov/cancer-preventing-infections/patients/fever.html