Growth-Factor Injections (G-CSF) & Bone Pain Management

After a growth-factor shot, a deep ache can settle into your back and legs. It is sometimes strong enough to wake you up. Many people are never warned, so they assume something has gone wrong. It has not. This ache is the most commonly reported effect of these injections. Knowing that in advance changes how it feels.

Chemotherapy can lower your neutrophils, the white cells that fight infection. Growth-factor injections reduce that risk.

Filgrastim products — Granix, Neupogen, Nivestym, Releuko, Zarxio — "are used to decrease the chance of infection" in people receiving chemotherapy. They work "by helping the body make more neutrophils," according to MedlinePlus. Filgrastim is injected under the skin or into a vein, "usually given once a day."

Pegfilgrastim — Fulphila, Neulasta, Nyvepria, Udenyca, Ziextenzo — is described by NCI as "a form of filgrastim that has polyethylene glycol (PEG) attached to it. This form stays in the body longer than does filgrastim, so it doesn't need to be given as often." It comes as a prefilled syringe or autoinjector. It is "usually given as a single dose for each chemotherapy cycle, no sooner than 24 hours after the last dose of chemotherapy of the cycle is given."

The FDA prescribing information for Neulasta states that the "Most common adverse reactions (≥ 5% difference in incidence compared to placebo) are bone pain and pain in extremity." The label's trial table gives numbers. Bone pain was reported by 31% of people receiving Neulasta, versus 26% on placebo. Pain in an arm or leg was reported by 9%, versus 4%.

These drugs tell your bone marrow to speed up production of white blood cells. The American Cancer Society describes growth factors as "hormone-like substances that help bone marrow make new blood cells." Marrow sits inside your bones. That is why the ache is felt there.

Now the limits, honestly. The drug information reviewed here lists bone pain as an effect. It does not spell out the precise biological reason it occurs. A site offering a confident one-sentence explanation is going beyond what the labels say.

MedlinePlus lists the effects of filgrastim as "bone, joint, back, arm, leg, mouth, throat, or muscle pain." It also lists headache, rash, nausea, vomiting, and "tiredness, lack of energy." For pegfilgrastim it lists "bone pain" and "pain in arms or legs." So the ache is not limited to one spot.

The evidence here is thin. Neither the MedlinePlus pages nor the Neulasta label states how many days the pain typically lasts. MedlinePlus does say what to do. Report these symptoms if they "are severe or do not go away."

Start by describing the pain precisely. NCI suggests telling your team several things. Where you feel it. What it feels like — sharp, burning, shooting, or throbbing. Whether it is constant or comes and goes. When it starts, and how long it lasts. And how bad it is on a scale of 1 to 10.

For treatment-related pain, NCI lists "over-the-counter pain medicine such as aspirin, acetaminophen (Tylenol), ibuprofen (Advil), or naproxen (Aleve)." It also lists prescription options including steroids, and opioids "for moderate to severe cancer pain." Ask your team which is right for you rather than choosing on your own.

NCI is direct about follow-up: "Contact your doctor or nurse if you feel new pain, if your pain isn't decreasing or going away with pain medicine, or if you have side effects from the pain medicine."

You may hear that an over-the-counter antihistamine helps this ache. The research is not settled, and none of the sources reviewed here recommend it. Raise it with your team rather than treating it as established.

Some symptoms are not part of the expected ache. MedlinePlus says to call your doctor immediately if you have:

• "pain in the left upper part of the stomach or the tip of your left shoulder"
• "fever, shortness of breath, trouble breathing, fast breathing"
• "trouble breathing, coughing up blood"
• "swelling of the face, throat, or around the mouth or eyes; hives; rash," or wheezing
• "unusual bleeding or bruising," or "purple markings under the skin"
• "swelling of stomach area or other swelling, decreased urination"
• "painful, urgent, or frequent urination"

Left upper stomach or left shoulder pain deserves special attention. The Neulasta label instructs clinicians to "Evaluate patients who report left upper abdominal or shoulder pain for an enlarged spleen or splenic rupture." That is a different place. And it means something different from an ache in your back and legs.

MedlinePlus also states: "If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911."

• National Cancer Institute: Filgrastim. https://www.cancer.gov/about-cancer/treatment/drugs/filgrastim
• National Cancer Institute: Pegfilgrastim. https://www.cancer.gov/about-cancer/treatment/drugs/pegfilgrastim
• MedlinePlus (NIH): Filgrastim Injection. https://medlineplus.gov/druginfo/meds/a692033.html
• MedlinePlus (NIH): Pegfilgrastim Injection. https://medlineplus.gov/druginfo/meds/a607058.html
• DailyMed (NLM): NEULASTA (pegfilgrastim) prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=fdfe5d72-6b80-435a-afa4-c5d74dd852ce
• National Cancer Institute: Pain. https://www.cancer.gov/about-cancer/treatment/side-effects/pain
• American Cancer Society: Supportive Therapy for Myelodysplastic Syndromes. https://www.cancer.org/cancer/types/myelodysplastic-syndrome/treating/supportive-therapy.html