Pegfilgrastim (Neulasta): Timing, On-Body Injector, Biosimilars and Bone Pain

By the Oncol.net editorial team · Last updated November 1, 2026

Pegfilgrastim (Neulasta) is a once-per-cycle injection that helps your bone marrow rebuild infection-fighting neutrophils after chemotherapy. The usual adult dose is 6 mg, given at least 24 hours after chemotherapy and not within 14 days before the next cycle. An on-body injector can deliver it about 27 hours after being applied. Bone pain is the most common side effect, reported by about 3 in 10 people in trials.

What pegfilgrastim is and how it works

Pegfilgrastim is not chemotherapy, and it does not treat the cancer. It is a growth factor, a lab-made version of G-CSF (granulocyte colony-stimulating factor), a natural protein that tells your bone marrow to make more neutrophils. Neutrophils are the white blood cells that fight infection.

Chemotherapy lowers neutrophils, a condition called neutropenia. If you get a fever while they are low, it is called febrile neutropenia, and it can be life-threatening. Pegfilgrastim helps your marrow make neutrophils sooner, so the dangerous window is shorter.

It is filgrastim with a long chain called PEG attached, which makes it last much longer in the body. Your own neutrophils help clear the drug. As they recover, the drug is cleared more quickly. Its half-life, the time for the level to fall by half, ranges from 15 to 80 hours.

Who gets it and how well it works

Pegfilgrastim is approved for people with non-myeloid cancers (cancers not arising from the white cell line that makes neutrophils) who are getting chemotherapy with a real risk of febrile neutropenia. Not everyone on chemotherapy needs it. Neulasta is also approved after high-dose radiation exposure, but that is a different dose schedule.

It is not approved for collecting stem cells for transplant. It is also not approved for myeloid cancers such as AML, and the label cannot rule out that it may act as a growth signal for some tumors.

The main placebo-controlled trial enrolled 928 people with breast cancer on docetaxel every 21 days:

Result	Pegfilgrastim	Placebo
Febrile neutropenia	1%	17%
Hospital stay for febrile neutropenia	1%	14%
IV antibiotics or other anti-infective drugs	2%	10%

These numbers come from one regimen, so your own risk may be different. Pegfilgrastim lowers the risk of infection but does not remove it, so still call about any fever.

Timing relative to chemotherapy

The standard adult dose is 6 mg, injected under the skin, once per chemotherapy cycle. Children under 45 kg (about 99 pounds) get a weight-based dose.

The label sets a clear rule. Do not give it between 14 days before and 24 hours after chemotherapy. In plain terms:

Wait at least 24 hours after chemotherapy ends. In the main trials it was given on day 2 of the cycle.
Leave at least 14 days before your next chemotherapy starts.

The reason is that the drug pushes marrow cells to divide. The filgrastim label explains that rapidly dividing marrow cells may be more sensitive to chemotherapy, so the two should not overlap.

If you get a multi-day regimen, or a pump that runs for 2 days, the 24 hours is counted from the end of chemotherapy. If your cycles are 14 days or shorter, ask how your team is handling timing. The label's window is tight for these schedules. If your appointment is hard to reach, tell your team. They may be able to use an on-body injector.

The on-body injector

An on-body injector is a small device stuck to your skin at the chemotherapy visit. It gives the dose automatically the next day, so you do not need to come back. Two US products use one:

Product	Delivery starts	Delivery takes
Neulasta Onpro	About 27 hours after it is applied	About 45 minutes
Udenyca Onbody	About 27 hours after it is applied	About 5 minutes

A health professional fills the device and puts it on your abdomen or the back of your arm. The arm can be used only if a caregiver can watch the device. The dose must arrive at least 24 hours after chemotherapy. For Neulasta Onpro, the label says to:

Have someone nearby for your first use.
Avoid travel, driving or operating machinery during hours 26 to 29 after it is applied.
Keep it dry for about the last 3 hours before delivery, so that you can spot a leak.
Keep it at least 4 inches from phones, microwaves and other electrical equipment.
Keep it between 41°F and 104°F (5°C and 40°C).
Avoid X-rays, CT, MRI, ultrasound, radiation treatment and hyperbaric oxygen while wearing it. Ask for a pat-down at the airport.
Avoid hot tubs, baths, saunas, direct sun, and sleeping on it. Keep lotions and oils away from it.
Skip lotions and oils on your arms and abdomen before your next dose, so it sticks well.
Remove it only after the light stays solid green, and place it in a sharps container.

Call your care team right away if the status light flashes red, the device comes off, it leaks, or the adhesive becomes noticeably wet. Do not put it back on. You may have received only part of your dose or none, and your team may give a new dose by syringe as soon as possible. Missed or partial doses raise your risk of neutropenia and infection.

If you react to acrylic adhesive, tell your team. The device's adhesive may cause a significant skin reaction, and a syringe may suit you better. The device is used only with its own packaged syringe.

Biosimilars

A biosimilar is a biologic medicine that is highly similar to an already approved one. The FDA requires that it have no clinically meaningful differences from the original. Neulasta's biosimilars each have a four-letter suffix on the generic name:

Brand	Generic name
Armlupeg	pegfilgrastim-unne
Ennumo	pegfilgrastim-pccg
Fulphila	pegfilgrastim-jmdb
Fylnetra	pegfilgrastim-pbbk
Nyvepria	pegfilgrastim-apgf
Stimufend	pegfilgrastim-fpgk
Udenyca	pegfilgrastim-cbqv
Ziextenzo	pegfilgrastim-bmez

The dose and timing rule stay the same. Devices do differ, so ask which product you are getting, and follow the instructions that come with it.

Pegfilgrastim vs. filgrastim

Both are G-CSF drugs. The main difference is how often you get them. Read our page on filgrastim for more.

	Pegfilgrastim (Neulasta)	Filgrastim (Neupogen)
How often	Once per chemotherapy cycle	Once a day
Typical adult dose	6 mg, the same for any adult weight	Starts at 5 mcg per kg a day
How long	One dose	Up to 2 weeks, or until neutrophils reach 10,000/mm³ after the low point
Timing around chemo	Not from 14 days before until 24 hours after	Not from 24 hours before until 24 hours after
How given	Injection under the skin, or on-body injector	Injection under the skin, or into a vein

In the two head-to-head breast cancer trials, the average days of severe neutropenia in cycle 1 were close: 1.8 and 1.7 days with pegfilgrastim, and 1.6 with filgrastim. Filgrastim's shorter action makes it easier to fit around short gaps between chemotherapy doses. Pegfilgrastim saves daily injections.

Side effects and bone pain

Bone pain is the main side effect. In placebo-controlled trials, 31% of people on pegfilgrastim had bone pain, compared with 26% on placebo. Pain in the arms or legs affected 9% and 4%. Both groups were on chemotherapy, which is why placebo rates are high too.

In the NOLAN study of 600 women with breast cancer, moderate or severe pain peaked around day 3, counting from the injection day, and then fell. Bone pain was most common in the first cycle.

What helps with bone pain

Ask your team before you take anything. Pain relievers can hide a fever, and aspirin or ibuprofen-type drugs may not be safe with your platelet count or kidney function.

NOLAN tested naproxen and the antihistamine loratadine for 5 days starting on the injection day. All-grade bone pain in cycle 1 was 40% with naproxen, 43% with loratadine and 47% with neither. Those differences were not statistically significant. Some patient-reported pain scores were lower with either drug. Loratadine caused fewer side effects, so the authors suggested considering it. The study was open label and funded by the maker of Neulasta, so treat this as limited evidence. Read more about managing pain.

Your bones may also show changes on a bone scan for a short time. Tell the imaging team you had this drug, so the scan is not misread.

Serious warnings and when to call

Ruptured spleen. This is rare but can be fatal. Watch for pain in the upper left belly or the tip of the left shoulder.
Lung injury (ARDS). Fever with trouble breathing needs urgent care.
Severe allergic reaction. Most happen with the first dose, and can come back within days. People allergic to filgrastim or pegfilgrastim should not take it.
Sickle cell crisis. Severe and sometimes fatal crises have occurred. Tell your team if you have a sickle cell disorder.
Kidney inflammation (glomerulonephritis). Watch for facial or ankle swelling, dark or bloody urine, or less urine.
Capillary leak syndrome. Fluid leaks from blood vessels. Signs include swelling, dizziness, and unusual tiredness. It can be life-threatening if treatment is delayed.
Inflammation of large arteries (arteritis or aortitis). It may start in the first week, with fever, belly or back pain, headache, neck pain and feeling unwell.
Very high white cells or low platelets. Your team watches your blood counts.
Blood cancers. MDS and AML have been linked with its use alongside chemotherapy or radiation in breast and lung cancer. Your team monitors for signs of these.

Call your care team now if you have: a temperature of 100.4°F (38°C) or higher; upper left belly or left shoulder pain; shortness of breath; swelling of the face or ankles; dark or bloody urine; unusual bruising or bleeding; or fever with back pain, belly pain, headache or neck pain. Call 911 for severe trouble breathing or swelling of the mouth or throat. See when to call your doctor and our guide to fever during chemotherapy.

Precautions, pregnancy and breastfeeding

The Neulasta label does not list specific drug interactions. The main concern is timing with chemotherapy. The cyclophosphamide label notes that G-CSF drugs may add to its lung risk, so report new breathlessness.

Tell your team if you are pregnant, may become pregnant, or are breastfeeding. Data on pegfilgrastim in pregnancy are too limited to know whether it carries a risk. Studies of filgrastim products have not linked them with birth defects or miscarriage. There are no data on pegfilgrastim in breast milk. Other filgrastim products pass poorly into breast milk. Remember that the chemotherapy itself may rule out pregnancy or breastfeeding, so ask about both.

Frequently asked questions

How soon after chemo can I have Neulasta?

At least 24 hours after chemotherapy ends. The label says not to give it between 14 days before and 24 hours after chemotherapy. In the main trials it was given on day 2 of each cycle.

Why can't I have Neulasta the same day as chemo?

Pegfilgrastim pushes marrow cells to divide, and dividing cells may be more sensitive to chemotherapy. That is why the label asks for a gap of at least 24 hours. An on-body injector can be applied on the chemo day because it does not deliver the drug until about 27 hours later.

How long does Neulasta bone pain last?

In the NOLAN study, moderate or severe pain peaked around day 3, counting from the injection day, and then fell. It was most common in the first cycle. Tell your team if pain is severe or does not settle, and ask before taking any pain reliever.

Does Claritin help Neulasta bone pain?

It may help a little, but the evidence is limited. In the NOLAN study, all-grade bone pain was not significantly lower with loratadine (Claritin) or naproxen than with neither, though some pain scores were lower. Loratadine had fewer side effects than naproxen. Ask your team before taking either one.

What should I do if my Neulasta Onpro comes off or leaks?

Call your care team right away and do not put it back on. Also call if the light flashes red or the adhesive becomes noticeably wet. You may have missed part or all of your dose, and your team may give a replacement dose by syringe as soon as possible.

Can I shower or travel with the on-body injector?

Follow the instructions from your clinic. Keep the device dry for about the last 3 hours before delivery, and avoid baths, hot tubs and saunas. Avoid travel, driving or using machinery in hours 26 to 29 after it is applied. Ask for a pat-down at airport security instead of an X-ray scan.

Is a biosimilar as good as Neulasta?

The FDA requires biosimilars to be highly similar to the original, with no clinically meaningful differences. They use the same 6 mg dose and the same timing rule. Devices differ, so check how yours is used.

Is pegfilgrastim better than filgrastim?

Neither is simply better. Pegfilgrastim is one injection per cycle, while filgrastim is a daily injection. Trials found close results for days of severe neutropenia. Filgrastim's short action can be useful when chemotherapy is given close together, and your team will choose what fits your schedule.

Sources

This page is general information, not medical advice. Your care team knows your situation and should guide your decisions.