Zilbrysq (zilucoplan) can cause side effects that range from mild to serious. More common side effects include injection site reactions and diarrhea. If side effects become difficult to tolerate, talk with your doctor about coping tips or other treatment options.

Zilbrysq is a prescription drug used to treat generalized myasthenia gravis in certain adults. It’s given as an injection under your skin.

Keep reading to learn about the common, mild, and serious side effects Zilbrysq can cause.

Zilbrysq has a boxed warning. This is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Boxed warnings for Zilbrysq” section.

Zilbrysq can cause certain side effects, some more common than others. These side effects may be temporary, lasting a few days to weeks. Talk with your doctor if side effects do not go away, get worse, or become too difficult to tolerate.

Zilbrysq’s commonly reported side effects include:

For more information about some of these side effects, see the “Tips for managing side effects” section.

Mild side effects have been reported with Zilbrysq. These include:

In most cases, these side effects should be temporary, and some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. Do not stop Zilbrysq treatment unless your doctor recommends it.

Zilbrysq may cause mild side effects other than those listed here. See the drug’s prescribing information for details.

For more information about some of these side effects, see the “Tips for managing side effects” section.

Zilbrysq may cause serious side effects. The following list may not include all possible serious side effects of the drug. For more information, you can refer to Zilbrysq’s prescribing information.

If you develop serious side effects during Zilbrysq treatment, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported with this drug include:

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect during treatment with Zilbrysq and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

Allergic reaction

For some people, Zilbrysq can cause an allergic reaction, but this side effect wasn’t reported in the drug’s studies.

In general, symptoms of an allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should continue Zilbrysq treatment.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Zilbrysq, they may have you switch to a different treatment.

Zilbrysq has a boxed warning for the risk of serious meningococcal infections. A boxed warning is the most serious warning from the FDA. It alerts doctors and patients about drug effects that may be dangerous.

Zilbrysq increases the risk of serious and life threatening infections caused by the bacterium Neisseria meningitidis. These meningococcal infections include meningitis and sepsis.

Due to this risk, Zilbrysq is only available through a program called the Zilbrysq REMS (Risk Evaluation and Mitigation Strategy). Doctors or other healthcare professionals who prescribe Zilbrysq must enroll in this program.

What you can do

To help prevent meningococcal infection, REMS programs require you to be up to date on your meningococcal vaccines at least 2 weeks prior to starting Zilbrysq. Your doctor will also closely monitor you for symptoms of meningococcal infections after you start treatment, even after you’ve been vaccinated.

If you have questions about this Zilbrysq warning, talk with your doctor or pharmacist.

There may be things you can do to help make certain Zilbrysq side effects more manageable. If you have ongoing, worsening, or bothersome side effects, talk with your doctor or pharmacist. They can suggest tips for managing them or recommend other available treatment options for your condition.

Injection site reactions

Injection site reactions were a common side effect reported in studies of Zilbrysq.

Injection site reactions can cause symptoms such as:

Steps you can take to manage symptoms associated with this side effect include:

  • asking for a prescription numbing cream to apply to the site before receiving the injection
  • applying ice to the site before and after the injection (for no more than 15 minutes at a time)
  • taking acetaminophen (Tylenol) to help relieve injection pain

Injection site reactions will likely become less painful over time. But if symptoms become worse or difficult to tolerate, talk with your doctor or pharmacist.

Nausea and vomiting

Nausea and vomiting were common side effects reported in Zilbrysq studies. Nausea can lead to vomiting, which can lead to dehydration.

Steps you can take to manage symptoms associated with this side effect include:

  • try the BRAT diet (bananas, rice, applesauce, and toast) or eat other bland foods, such as:
    • baked potato
    • plain pasta
    • hard-boiled or scrambled eggs
    • saltines
  • eat a small piece of fresh or candied ginger
  • drink chamomile tea, ginger tea, or peppermint tea
  • apply a cool compress to the back of your neck
  • recline with your upper body elevated, and move around as little as possible
  • take over-the-counter nausea medications (antiemetics) such as:

Be sure to drink water throughout each day to help keep your body hydrated.

If you develop nausea that becomes severe or doesn’t go away, tell your doctor. If you’re dehydrated due to vomiting, they may suggest medical care. This may include giving you intravenous (IV) fluids (through a vein). They may also prescribe an antiemetic such as ondansetron (Zofran).

Upper respiratory infection

Upper respiratory infection, such as the common cold, was a mild but common side effect reported in Zilbrysq studies.

Symptoms may include:

Tell your doctor if you have an infection before starting Zilbrysq. They’ll likely treat the infection before you start treatment. If you develop an upper respiratory infection during Zilbrysq treatment, call your doctor. They’ll do a diagnosis based on your symptoms and suggest treatment options. They may have you temporarily stop Zilbrysq until your infection clears up.

Consider the following important information before starting Zilbrysq.

Zilbrysq has a boxed warning. This is the most serious warning from the FDA. For details, see “Boxed warnings for Zilbrysq.”

Other precautions

Before starting Zilbrysq, discuss your health history with your doctor. This medication may not be right for you if you have certain medical conditions or other factors that affect your health. Be sure to tell your doctor if any of the following apply to you:

  • any infections, including those caused by Neisseria meningitidis
  • pancreatitis
  • previous allergic reaction to this or a similar drug
  • pregnancy
  • breastfeeding

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.