Hemgenix

Treatment of Hemophilia B

Hemgenix is used to treat adults with hemophilia B, which is also known as congenital Factor IX deficiency. This condition is caused by a missing or defective gene that prevents the body from producing enough Factor IX, a protein essential for blood clotting. Without enough Factor IX, individuals may experience prolonged bleeding after an injury or spontaneous internal bleeding that can damage joints and organs.

This treatment is typically prescribed for adults who meet specific clinical criteria, including those who:

• Currently use Factor IX prophylaxis therapy to manage or prevent bleeding episodes.
• Have a current or historical occurrence of life-threatening bleeding.
• Experience repeated and serious spontaneous bleeding episodes.

The purpose of this therapy is to enable the body to produce its own Factor IX, which may reduce the frequency of bleeding events and the need for regular factor replacement infusions.

Mechanism of Action

Hemophilia B is caused by a mutation in the gene responsible for producing Factor IX, a protein necessary for blood to clot. Hemgenix uses gene therapy technology to address this deficiency directly.

The treatment consists of a modified, harmless virus known as a viral vector. This vector acts as a delivery system to transport a working copy of the Factor IX gene into the liver cells. The virus itself does not cause disease and cannot replicate inside the body.

Once the functional gene reaches the liver, the following occurs:

• Protein Synthesis: The liver cells begin using the new genetic instructions to manufacture the Factor IX protein.
• Bloodstream Integration: The newly produced Factor IX is released into the blood, where it helps the body form clots normally.
• Bleeding Prevention: With higher levels of Factor IX circulating in the body, patients experience fewer bleeding episodes and a reduced need for frequent protein replacement injections.

This approach is intended as a one-time infusion. By providing the liver with a permanent set of instructions to create the missing protein, the therapy aims to provide long-term protection against bleeding complications associated with Hemophilia B.

Common Side Effects

The most frequently reported side effects of Hemgenix include:

• Increased liver enzymes (ALT or AST)
• Headache
• Flu-like symptoms
• Nausea
• Fatigue or feeling generally unwell
• Elevated blood levels of creatine kinase

Serious Side Effects

Some side effects can be serious and require medical attention or long-term monitoring:

• Infusion-related reactions: During or shortly after the infusion, some patients may experience symptoms such as chest tightness, dizziness, shivering, or high blood pressure.
• Liver toxicity: Hemgenix can cause inflammation of the liver. Healthcare providers monitor liver enzyme levels through blood tests every week for several months after the infusion to check for signs of injury.
• Risk of cancer: As a gene therapy, there is a theoretical risk that the treatment could contribute to the development of liver cancer (hepatocellular carcinoma). Regular ultrasounds and blood tests are typically recommended for ongoing monitoring, particularly in patients with existing risk factors for liver disease.

Infusion Reactions

Infusion-related reactions can occur during or shortly after the administration of Hemgenix. Symptoms may include chest tightness, headaches, abdominal pain, lightheadedness, or flu-like symptoms. Healthcare providers typically monitor patients during the infusion and for at least three hours afterward to manage any immediate reactions.

Liver Health and Monitoring

Elevations in liver enzymes, known as transaminitis, are common after treatment. These elevations may indicate an immune response that could reduce the effectiveness of the medication. To manage this risk, the following steps are typically taken:

• Liver enzyme levels are monitored weekly for at least three months following the infusion.
• Corticosteroids may be prescribed if liver enzyme levels rise above a certain threshold to protect liver function and maintain the treatment's efficacy.
• Regular monitoring continues for a longer period if enzymes remain elevated or while corticosteroids are being tapered.

Risk of Liver Cancer

There is a theoretical risk of developing hepatocellular carcinoma (a type of liver cancer) because the viral vector used in the treatment can integrate into the DNA of liver cells. While this specific complication was not observed in clinical trials for Hemgenix, annual liver health screenings are recommended for patients with existing risk factors, such as cirrhosis, chronic hepatitis B or C, or non-alcoholic fatty liver disease. These screenings usually involve an ultrasound and a blood test for alpha-fetoprotein.

Donation Restrictions

Individuals who have received Hemgenix are advised not to donate blood, organs, tissues, or cells for transplantation. This is a precautionary measure due to the permanent nature of gene therapy.

Pre-existing Immunity

The presence of pre-existing antibodies against the viral vector (AAV5) used in Hemgenix may affect how well the treatment works. While clinical trials included patients with these antibodies, healthcare providers may still consider this factor when determining the appropriateness of the therapy.

Pregnancy

Hemgenix is a gene therapy indicated for the treatment of adults with Hemophilia B. Because Hemophilia B primarily affects males and the medication is approved for use in adult males, there is no information available regarding its use in pregnant women. No animal reproductive studies have been conducted with this medication to evaluate potential risks to a fetus.

Breastfeeding

It is not known whether Hemgenix is present in human milk or if it has any effects on a breastfed infant or milk production. Because the medication is intended for use in adult males, data regarding its safety during lactation are not available.

Patients should discuss any questions regarding reproductive health or the use of gene therapy with their healthcare provider.

Dosage Forms

Hemgenix is available as a suspension for intravenous infusion. It is a sterile, clear to slightly opalescent, and colorless liquid.

Strengths and Packaging

The medication is supplied in single-dose vials. Because the total dose is calculated based on the patient's body weight, Hemgenix is distributed in kits that contain a specific number of vials. These kits may include:

• Between 10 and 48 vials per kit.

Each vial contains a standardized concentration of the active ingredient, etranacogene dezaparvovec-drlb. The healthcare provider determines the exact number of vials needed for a single one-time infusion based on the patient's weight in kilograms.

FDA Approval Status

The U.S. Food and Drug Administration (FDA) approved Hemgenix in November 2022. It is classified as an adeno-associated virus vector-based gene therapy and was the first gene therapy approved for the treatment of Hemophilia B.

Approved Indications

Hemgenix is approved for use in adults with Hemophilia B (congenital Factor IX deficiency). It is specifically indicated for patients who meet at least one of the following criteria:

• They currently use Factor IX prophylaxis therapy.
• They have a current or historical life-threatening hemorrhage.
• They experience repeated, serious spontaneous bleeding episodes.

Safety and Monitoring

The FDA has not issued a boxed warning for Hemgenix. Regulatory labeling requires healthcare providers to monitor patients for adverse reactions during the infusion and to perform regular blood tests to check liver enzyme levels for several months following treatment to monitor for potential liver injury.

Treatment Cost

The list price for Hemgenix is approximately $3.5 million per dose. It is administered as a single, one-time intravenous infusion. While the initial cost is high, the treatment is designed to provide long-term production of Factor IX, which may reduce or eliminate the need for ongoing prophylactic infusions that are traditionally required for hemophilia B management.

Insurance and Financial Assistance

The actual out-of-pocket cost to a patient depends on several factors, including:

• Insurance Coverage: Most private and public health insurance plans require a detailed prior authorization process before approving coverage for gene therapy.
• Negotiated Rates: The final cost paid by insurers often differs from the list price due to negotiated discounts or value-based payment arrangements.
• Patient Support Programs: The manufacturer may offer financial assistance or navigation services to help eligible patients understand their coverage and manage costs.

Patients are encouraged to work closely with their healthcare provider and insurance company to determine specific coverage details and any potential financial responsibilities before starting treatment.