Hemgenix Side Effects: What to Expect and When to Call Your Doctor

Hemgenix (etranacogene dezaparvovec-drlb) was evaluated in 57 adults with moderately severe to severe hemophilia B across two clinical studies — a Phase 2b trial of 3 patients and the pivotal Phase 3 HOPE-B trial of 54 patients. Importantly, no serious adverse reactions were reported in clinical trials. However, Hemgenix does have important side effects and monitoring requirements that every patient should understand before treatment.

The Most Common Side Effects of Hemgenix (Occurred in ≥5% of Patients)

The following adverse reactions were reported in at least 5% of patients in the clinical trials:

Elevated ALT (alanine aminotransferase): The most commonly reported side effect. Elevated liver enzymes were seen in 24 of 54 patients in the HOPE-B trial. Most elevations were asymptomatic, occurred in the first 4 months post-infusion, and resolved either spontaneously or with corticosteroid treatment.

Headache: Reported in a significant proportion of patients, typically mild to moderate.

Blood creatine kinase (CK) elevations: Elevations in this muscle enzyme marker were observed post-infusion. Generally asymptomatic.

Flu-like symptoms: Including fever, chills, body aches, and fatigue. Usually transient.

Infusion-related reactions (IRRs): Occurred in approximately 33% of patients. Symptoms include chest tightness, headache, abdominal pain, lightheadedness, shivering, flushing, rash, and elevated blood pressure. Most resolved within a day.

Fatigue and malaise: General tiredness and feeling unwell were reported by multiple patients, typically in the early post-infusion period.

Elevated AST (aspartate aminotransferase): Elevated in 19 of 54 patients in the HOPE-B trial, often occurring alongside ALT elevations.

The Most Serious Risk: Hepatotoxicity

The most important warning associated with Hemgenix is immune-mediated hepatotoxicity — liver damage caused by your immune system attacking the liver cells that have been transduced by the AAV5 vector.

Here is what to know:

Liver enzyme elevations are closely monitored: your doctor will test your ALT and AST weekly for the first 3 months, then monthly for up to 1 year after infusion.

If ALT rises above the upper limit of normal, your doctor will likely start a course of corticosteroids (such as oral prednisolone 60 mg/day) with a subsequent taper. The average corticosteroid treatment duration in clinical trials was 81.4 days.

Elevated liver enzymes can also reduce the effectiveness of Hemgenix by damaging transduced hepatocytes (liver cells that are producing Factor IX).

Avoid hepatotoxic agents (including alcohol, certain herbal supplements, and potentially hepatotoxic medications) especially in the first year post-infusion, as these can worsen liver damage.

Infusion-Related Reactions: What Happens During Administration

During the Hemgenix infusion, medical staff will monitor you continuously. The infusion is delivered at a maximum rate of 500 mL/hour and typically takes several hours, depending on your weight (patients weighing 126–130 kg receive approximately 252–260 mL of drug, plus saline carrier).

You will also be monitored for at least 3 hours after the infusion ends. If an infusion-related reaction occurs:

The infusion may be slowed or temporarily stopped

Antihistamines and/or corticosteroids may be given to manage symptoms

In rare cases of anaphylaxis, emergency treatment will be initiated — this is why administration only occurs at centers equipped for emergency response

Long-Term Monitoring: What to Expect for Up to 5 Years

Hemgenix requires long-term monitoring beyond the first year:

Factor IX activity monitoring continues weekly for 3 months, then periodically over time to assess durability of expression.

Patients with preexisting liver cancer risk factors (such as prior hepatitis B or C, cirrhosis, or alcohol use) require liver ultrasound and alpha-fetoprotein (AFP) monitoring for up to 5 years due to the theoretical (but not yet observed in Hemgenix patients) risk of hepatocellular carcinoma from AAV vector integration.

Patients should not donate blood, organs, tissues, or cells after receiving Hemgenix due to vector distribution in the bloodstream.

When to Call Your Doctor After Hemgenix

Contact your hemophilia treatment center immediately if you experience:

Yellowing of the skin or eyes (jaundice)

Severe abdominal pain, especially in the upper right quadrant

Unexplained bleeding or bruising (may indicate diminishing Factor IX activity)

Signs of allergic reaction: hives, difficulty breathing, swelling of face, lips, or throat

For information on drug interactions with Hemgenix, read Hemgenix Drug Interactions. And if you're still searching for a center near you with Hemgenix available, medfinder.com can help.