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Plegridy: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on April 4, 2023.

1. How it works

  • Plegridy is a brand (trade) name for peginterferon beta-1a which may be used to treat certain types of multiple sclerosis (MS) in adults.
  • Plegridy is a type of interferon. Interferons are a group of proteins that are produced naturally by the body in response to viral infections. Experts aren’t sure exactly how Plegridy works for MS but believe it helps control immune system activities, preventing the immune system from attacking the myelin sheath. Plegridy helps to inhibit inflammation that can cause MS flare-ups. Plegridy may also help slow the progression of physical disability associated with MS and reduce the number of relapses.
  • Plegridy contains interferon beta-1a that has polyethylene glycol added to it to make it pegylated interferon. Adding a polyethylene glycol molecule to standard interferon extends its activity allowing it to stay in the body much longer. This means it only needs to be injected once every two weeks, instead of three times a week for standard interferon.
  • Plegridy belongs to the class of medicines known as interferons.

2. Upsides

  • May be used to treat relapsing forms of multiple sclerosis in adults. This includes clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.
  • Administered by subcutaneous (SC) injection under the skin or intramuscular (IM) injection once every two weeks (14 days). Standard interferon needs to be administered three times a week. People can be taught how to self-administer Plegridy.
  • Although Plegridy does not cure MS it helps reduce the symptoms of MS and decrease the number of relapses.
  • Plegridy is available as a pen and prefilled syringe each containing 125 micrograms of Plegridy for SC administration and a prefilled syringe containing 125 micrograms of Plegridy for IM administration. A starter pack containing lower dosages of Plegridy (63 micrograms and 94 micrograms) for use during initiation of Plegridy is also available.
  • Plegridy is administered SC into the abdomen, back of the upper arm, or thigh. When given IM, Plegridy should be injected into the upper thigh, and injection sites may be rotated between the left and right thighs.
  • At least 50% fewer injection site reactions were reported with IM versus SC administration of Plegridy (14.4% vs. 32.1%).

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Injection site reactions, including redness, swelling, itch, and pain at the injection site are some of the most common side effects reported with SC Plegridy. Injection site necrosis has also been reported that may require either temporary or permanent discontinuation.
  • Other side effects common to both SC Plegridy and IM Plegridy include headache, muscle or joint pain, influenza-like illnesses, fever, lack of energy, nausea, or vomiting. Plegridy may also increase your risk of seizures, congestive heart failure, decreased white blood cell counts, autoimmune disorders (such as idiopathic thrombocytopenia, hypothyroidism, or hyperthyroidism), and thrombotic microangiopathy (some fatal), and is rarely associated with anaphylaxis or other allergic reactions.
  • Plegridy suppresses the immune system and decreases the number of white blood cells in the body which may reduce a person's ability to fight infection. This ability will be further compromised if the person is also taking other drugs that suppress the immune system, such as chemotherapy agents, immune-modulating therapies, or other immunosuppressants. Plegridy may also lower platelet numbers which can increase the risk of bleeding or anemia.
  • Should not be used by anyone with a history of hypersensitivity to natural or recombinant interferon beta or peginterferon, or any other component of the formulation.
  • Monitor patients for signs and symptoms of hepatic injury. Elevations in hepatic enzymes (for example alanine aminotransferase of up to 5 times the upper limit of normal) and hepatic injury have been observed with the use of Plegridy in clinical studies. Severe hepatic injury, including hepatitis, autoimmune hepatitis, and rare cases of severe hepatic failure, have been reported with Plegridy.
  • Plegridy is associated with a higher rate of depression, suicidal ideation, and suicide compared with people taking a placebo (inactive medicine). Monitor patients for symptoms of depression or thoughts of suicide.
  • Cohort studies have not shown an increased risk of major birth defects associated with Plegridy, although findings for low birth rates or miscarriage have been inconsistent. Encourage women exposed to Plegridy during pregnancy to enroll in the pregnancy exposure registry by calling 1-866-810-1462 or at There is no information on the risks associated with using Plegridy during breastfeeding.
  • Plegridy pens and prefilled syringes need to be stored in a refrigerator between 36°F and 46°F (2°C to 8°C).
  • No generic version of Plegridy is available.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Plegridy is a type of interferon that may be used to treat adults with multiple sclerosis (MS) that can be self-administered either subcutaneously or intramuscularly. Injection-site reactions with SC Plegridy and flu-like symptoms are the most common side effects reported. Plegridy has been associated with a 36% reduction in the annualized rate of relapse of MS.

5. Tips

  • Plegridy is usually started at a low dose (63 micrograms), and the dose titrated up to 94 micrograms after 14 days, and then to 125 micrograms (full dose) after another 14 days.
  • Do not attempt to self-administer the Plegridy pen or syringe until your doctor, nurse, or other health care professional has taught you how to use it, and you have discussed the pros and cons of SC versus IM administration. There are different instructions for administering the syringe subcutaneously or intramuscularly. Do not remove the cap of the Plegridy pen or syringe until you are ready to inject it. If you do accidentally remove the cap of the pen, do not put it back on as this may cause the pen to lock.
  • Plegridy should be stored in a refrigerator between 36°F and 46°F (2°C to 8°C). If no refrigerator is available, they may be kept out of a refrigerator at room temperature (less than 77°F [25°C]) for up to 30 days; however, they should not be put back in a refrigerator after this time. Discard them instead.
  • Take your Plegridy pen or syringe out of the refrigerator and let it warm up naturally to room temperature for 30 minutes. Do not put it in the microwave or use hot water to heat it.
  • For SC use, the Plegridy pen may be easier to use. Wash your hands with soap and water. Check the injection status on your Plegridy pen. You should see green stripes in the injection status window. Also, check the expiry date located on the side of the pen.
  • Check how the injection fluid looks through the viewing window. It should be clear and colorless. Do not use it if it is cloudy or has particles floating in it. Air bubbles are normal and will not affect your dose.
  • Choose an injection site, such as your stomach, thigh, or the back of your arm (for SC administration), and wipe it with an alcohol wipe. Let it dry. Pull the Plegridy pen cap straight off. You will not see the pen needle as it is hidden. Place the pen or the tip of the needle on your chosen injection site at a 90° angle (straight up and down). Firmly press and hold down the Plegridy pen. This will insert the needle and start the injection. You will hear a clicking sound. Hold the pen down firmly until the clicking sound stops and you see a green checkmark (tick) status where the green stripes used to be. After the clicking has stopped, remove your pen from the injection site. You should see a yellow plunger in the medicine viewing window. If there is blood at the injection site, hold gauze over the site to stop the bleeding and wipe away the blood.
  • Dispose of the used Plegridy pen in an approved sharps disposal container. Each Plegridy pen is administered just one time only. Never share your Plegridy pen with others.
  • When Plegridy is administered just under the skin (subcutaneously). the usual sites for self-administration are the stomach area (at least 2 inches [5cm] away from your belly button), upper thigh, or the back of your upper arm if somebody else is giving it to you. You should rotate sites for each injection (do not use the same site twice in a row) and you should not inject Plegridy where the skin is bruised, discolored, red, or infected, or if there is a rash on the skin. See your doctor if the skin where you injected the Plegridy does not heal normally. If you are experiencing a lot of injection site reactions, talk to your doctor about IM Plegridy.
  • To administer IM Plegridy, wash your hands with soap and water. Check the syringe for cracks, damage, or discoloration. With one hand, hold the prefilled syringe right under the cap by the ridged part with the cap pointing up. With the other hand, grasp the cap and bend it at a 90-degree angle until it snaps off. Take out the covered needle and press it on the syringe glass tip, gently turning to the right until it is firmly attached. If you are still titrating your dose, use the titration clips as per the package instructions. IM Plegridy should be injected into the muscle of the thigh, and you should inject into a different site on your thigh each time that is not bruised, scarred, or irritated. Wipe the site with an alcohol wipe and let dry. Pull the cover off the needle, and with the other hand, stretch the skin out tight around the injection site. Hold the syringe like a pencil and with a quick dart-like motion insert the needle at a 90-degree angle through the skin into the muscle. After the needle is in let go of the skin. Slowly push the plunger all the way down until it touches the collar. Pull the needle out then use a gauze pad to press down on the injection site for a few seconds. Discard the used syringe in a sharps container.
  • Plegridy is rarely associated with liver disease and may increase your risks of seizures, heart disease, depression, or suicide. Report any symptoms of liver disease (such as yellowing of the skin or eyes, abdominal pain or swelling, itchy skin, dark urine color, nausea or vomiting), shortness of breath, swelling of your lower limbs, easy bleeding or bruising, or changes in your mood to a doctor.
  • If you experience an allergic reaction while self-administering Plegridy seek urgent medical attention. Most people recover with antihistamines or corticosteroids; however, Plegridy should be discontinued if a serious reaction occurs.
  • Talk to your doctor about taking a prophylactic dose of acetaminophen or another pain-relieving/fever-lowering medication if you experience flu-like symptoms while prescribed Plegridy.
  • Although Plegridy has not been associated with an increased risk of major birth defects you should tell your doctor if you are planning a pregnancy before conceiving. If you become pregnant while taking Plegridy you should enroll in the pregnancy exposure registry by calling 1-866-810-1462 or at There is no information on the risks associated with using Plegridy during breastfeeding.

6. Response and effectiveness

  • Plegridy reduced the annualized rate of relapse by 36% in one study that compared Plegridy with a placebo (total number of participants: 1012). There was also a 67% relative reduction in the mean number of new or newly enlarging T2 hyperintense lesions and an 86% reduction in the mean number of Gd-enhancing lesions.
  • After 48 weeks, 18.7% of people taking Plegridy had experienced a relapse compared with 29.1% of people assigned a placebo.
  • Research has shown that people experienced significantly fewer injection site reactions with IM Plegridy compared with SC Plegridy (14.4 percent vs. 32.1 percent). The overall safety profiles were generally similar.

7. Interactions

Medicines that interact with Plegridy may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Plegridy. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Plegridy interacts with over 280 medications, but few of these interactions are considered major. Common medications that may interact with Plegridy include:

  • acetaminophen
  • antibiotics such as azithromycin, clavulanate, or erythromycin
  • anticonvulsants such as Divalproex or fosphenytoin
  • aspirin and NSAIDs such as diclofenac or ibuprofen
  • bupropion
  • cholesterol-lowering agents such as atorvastatin or simvastatin
  • contrast agents such as iohexol or iopamidol
  • dantrolene
  • fingolimod
  • heart medication ssuch as amiodarone, benazepril, or captopril
  • herbals, such as black cohosh, comfrey, or ginkgo
  • hydroxychloroquine
  • immunosuppressants such as azathioprine or cyclosporine
  • isotretinoin
  • ketoconazole or itraconazole
  • leflunomide or terifluonide
  • lomitapide
  • methotrexate
  • natalizumab
  • niacin
  • quinapril
  • tamoxifen
  • targeted therapies such as afatinib or alectinib
  • tramadol
  • vincristine
  • zidovudine.

Note that this list is not all-inclusive and includes only common medications that may interact with Plegridy. You should refer to the prescribing information for Plegridy for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Plegridy only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: April 4, 2023.