Spinraza (Nusinersen) Side Effects: What to Expect and When to Call Your Doctor

Spinraza (nusinersen) has now been used to treat spinal muscular atrophy for nearly a decade, providing an extensive body of real-world safety data. The drug has a well-established safety profile based on clinical trials and post-marketing surveillance, but it does carry important risks that patients and caregivers need to understand — especially because it is administered via lumbar puncture and has effects on blood clotting and kidney function.

This guide covers the full range of Spinraza side effects — from the common and manageable to the serious and potentially life-threatening.

Common Side Effects of Spinraza

The most common adverse reactions observed in clinical studies of Spinraza (low-dose regimen) were:

Respiratory infections (lower and upper) — including bronchitis, pneumonia, and upper respiratory tract infections. This is the most commonly reported adverse event, particularly in infants with SMA Type 1 who already have compromised respiratory muscle function.

Fever — reported in a significant portion of treated patients, often related to underlying respiratory infections.

Constipation — relatively common, particularly in infants and young children.

Headache — the most commonly reported symptom in older patients (children and adults) who can verbally report it; often related to post-lumbar puncture syndrome.

Vomiting — reported across age groups; often transient and procedure-related.

Back pain — reported in older patients; often related to the lumbar puncture procedure itself.

Atelectasis (partial lung collapse) — occurred in 18% of Spinraza-treated patients with infantile-onset SMA in Study 1.

Post-lumbar puncture syndrome — a cluster of symptoms including headache, nausea, and dizziness that occurs after lumbar puncture, typically resolving within days with rest and hydration.

Serious Side Effects: Know These Warning Signs

Spinraza carries several serious risks that require active monitoring before each dose and prompt medical attention if symptoms develop.

1. Thrombocytopenia (Low Platelet Count) and Bleeding Risk

Coagulation abnormalities and thrombocytopenia (abnormally low platelet count) have been observed with antisense oligonucleotide therapies including Spinraza. In controlled studies, 16% of Spinraza-treated patients developed platelet levels below the normal limit. Because platelets are essential for blood clotting, low platelets increase the risk of serious bleeding, including at the lumbar puncture site.

Your doctor will check platelet counts and coagulation studies before every Spinraza dose. Contact your doctor immediately if you notice:

Cuts or wounds that bleed for a long time or don't stop

Small red spots under the skin (petechiae)

Unexplained bruising or skin discoloration

Nosebleeds, bleeding gums, blood in urine or stool

Heavy or unusual menstrual bleeding

2. Kidney Damage (Glomerulonephritis)

Kidney toxicity, including potentially fatal glomerulonephritis (inflammation of the kidney's filtering units), has been reported with antisense oligonucleotide therapies. In controlled studies, 58% of Spinraza-treated patients had elevated urine protein, compared to 34% of sham-controlled patients. Your doctor will test your urine for protein before every dose.

Seek immediate medical attention for:

Decreased urine output or difficulty urinating

Swelling in the legs, ankles, or feet (edema)

Unexplained fatigue, weakness, or confusion

Shortness of breath not explained by SMA respiratory muscle involvement

3. Rare but Serious Post-Marketing Side Effects

Since Spinraza's approval, post-marketing surveillance has identified additional rare but serious adverse events:

Serious infections from lumbar puncture — including bacterial meningitis. Sterile technique is critical during administration.

Hydrocephalus — cases were reported in children and adults post-approval; causal relationship to Spinraza is unclear.

Hypersensitivity reactions — including angioedema, urticaria, and rash. Seek emergency care for symptoms of severe allergic reaction.

Aseptic meningitis — inflammation of the meninges without bacterial infection; has been reported post-approval.

Growth Effects in Infants

Spinraza may reduce growth as measured by height when administered to infants. This was observed in the controlled clinical study. It is currently unknown whether this effect is reversible if treatment is discontinued. Pediatric providers should monitor height regularly in infants receiving Spinraza.

When to Call Your Doctor Immediately

Contact your treatment center right away if you experience any of the following after a Spinraza injection:

Unexpected or excessive bleeding anywhere on the body

Symptoms of kidney problems (reduced urination, swelling, fatigue)

High fever, severe headache, neck stiffness (possible meningitis)

Signs of allergic reaction: hives, swelling of lips/tongue/throat, difficulty breathing

The 10-Year Safety Record

Despite these risks, Spinraza's safety profile is well-characterized and generally manageable with appropriate monitoring. The low-dose regimen has been studied in patients treated for up to 10 years, providing more long-term data than almost any other SMA therapy. The monitoring protocol before each dose — labs and urinalysis — is designed to catch problems early, before serious complications develop.

Also see: Spinraza Drug Interactions: What to Avoid and Tell Your Doctor for information on medications that may interact with Spinraza.

Need help finding a Spinraza treatment center or navigating access? Visit medfinder.com.