Isembyld (apitegromab-mstn) is a prescription medicine given as an IV infusion to treat spinal muscular atrophy (SMA) in adults and children aged 2 or older who are already being treated with a survival motor neuron 2 (SMN2)-targeted medicine. Like all medicines, Isembyld can cause side effects.
This article covers the common and serious side effects seen in clinical studies, along with practical tips for managing them at home and knowing when to call your health care provider. This isn't a complete list of all possible side effects. Always tell your health care provider about any symptom that concerns you or doesn't go away.
Common and Serious Side Effects of Isembyld
Common side effects of Isembyld include:
- Upper respiratory infections (cold-like symptoms)
- Vomiting
- Cough
- Other viral infections
- Headache
- Stomach flu (gastroenteritis)
- Sore throat (pharyngitis)
- Allergic-type reactions (hypersensitivity)
A possible serious side effect of Isembyld is bone fractures.
If you have symptoms that feel serious or life-threatening, seek medical care right away.
How to Manage Isembyld Side Effects
1. Fractures
Isembyld may increase the risk of bone fractures, including serious ones, which can happen with or without a fall or other injury. In the clinical study that supported Isembyld's approval, fractures occurred in about 9% of people who received the approved 10 mg/kg dose, compared with about 2% of people who received a placebo; some of those fractures affected the femur (thighbone). In an ongoing longer-term study, fractures (including some serious femur fractures) continued to occur over time, mostly in people who already had low bone density, a history of previous fractures, or joint contractures.
Possible signs of a fracture include:
- New or worsening pain in a bone, joint, or limb
- Swelling, bruising, or a visible deformity
- Difficulty or inability to bear weight or move a limb normally
Tell your health care provider right away if you notice any of these signs, even if you don't remember having a fall or injury. Inform your health care provider if you or your child has a history of low bone density or previous fractures before starting Isembyld; they may monitor you more closely. If a fracture does occur during treatment, your health care provider will weigh the risks and benefits of continuing Isembyld with you.
2. Infections (colds, viral illnesses, and sore throat)
Upper respiratory infections (the kind of symptoms you'd get with a common cold), other viral infections, and sore throat (pharyngitis) were among the most frequently reported side effects in people treated with Isembyld. Symptoms may include a stuffy or runny nose, sneezing, scratchy or sore throat, and cough.
To help manage these symptoms at home:
- Stay well hydrated with water, broth, or other fluids.
- Use a humidifier or breathe in warm steam to ease congestion.
- Try saline nasal sprays or rinses for stuffy nose.
- Gargle with salt water to soothe a sore throat.
In the clinical study, a small number of people treated with Isembyld also developed more serious respiratory infections, including pneumonia, and in rare cases, serious breathing problems. Contact your health care provider if cold or flu-like symptoms don't improve or if you or your child develops a fever. Seek medical care right away for trouble breathing, chest pain, or a high fever that doesn't come down with medicine.
3. Digestive symptoms (vomiting, diarrhea, stomach flu, and stomach pain)
Vomiting was one of the most common side effects reported with Isembyld. Stomach flu (gastroenteritis), diarrhea, and stomach pain were also reported more often with Isembyld than with placebo.
Tips that may help with vomiting and stomach flu symptoms:
- Take small sips of clear fluids, such as water or an electrolyte drink, to avoid dehydration.
- Eat bland foods, such as crackers, rice, or toast, once you're able to keep food down.
- Avoid greasy, spicy, or high-fat foods until symptoms settle.
- Rest as needed.
Tips that may help with diarrhea:
- Avoid caffeine, alcohol, and high-fiber or fried foods, which can make diarrhea worse.
- Ask your health care provider if an over-the-counter (OTC) antidiarrheal medicine can help you.
Contact your health care provider if vomiting or diarrhea is severe, lasts more than a day or two, or if you notice signs of dehydration, such as a very dry mouth, dizziness, or little to no urination.
4. Headache
Headache was a commonly reported side effect in people treated with Isembyld. Symptoms may include mild-to-moderate head pain or pressure.
To help manage headaches:
- Rest in a quiet, dark room if needed.
- Drink enough fluids throughout the day.
- Try relaxation techniques, such as deep breathing.
- Maintain a regular sleep schedule.
- Eat regular meals or snacks, and minimize stress where possible.
An OTC pain reliever may help ease headache pain, but check with your health care provider or pharmacist first to make sure it's safe for you or your child.
5. Allergic-type reactions and infusion reactions
Hypersensitivity (allergic-type) reactions were reported more often with Isembyld than with placebo. These include symptoms such as rash, itching, flushing, hives, or skin irritation and may happen during or shortly after an infusion.
Because Isembyld is given by IV infusion, your health care team will monitor you for a period of time during and after each infusion to check for any reaction. Tell your infusion team right away if you notice:
- A new rash, itching, hives, or skin redness
- Swelling of the face, lips, or throat
- Flushing or feeling warm all over
- Dizziness, trouble breathing, or chest tightness
Mild reactions may be managed by slowing the infusion or giving additional medicine, but seek medical care right away for symptoms like swelling of the face or throat, trouble breathing, or a severe skin reaction, as these can signal a serious allergic reaction.
Reducing Your Risk
A few general steps can help you manage side effects while using Isembyld:
- Ask your health care provider before starting or stopping any treatment, including Isembyld.
- Keep all recommended appointments, including bone density checks and blood tests, so your health care provider can monitor for side effects over time.
- Report any new or worsening symptoms to your health care provider, even if you're not sure they're related to Isembyld.
Your health care provider can adjust your treatment plan as needed based on how you respond to Isembyld. Don't change or stop treatment on your own without talking to them first.
