Forzinity: Everything You Need to Know About a New Medicine for Barth Syndrome

Barth syndrome is a rare genetic disorder that mostly affects males and can cause problems with the heart, muscles, and immune system. Common symptoms of Barth syndrome include weak muscles, tiredness, slow growth, frequent infections, and heart problems that may start within the first few months after birth.

There is no cure for Barth syndrome, and treatment usually focuses on managing the different problems that may arise. In September 2025, Forzinity (elamipretide) was approved to improve muscle strength in adults and children with Barth syndrome who weigh at least 66 pounds, making it the first medicine specifically approved for this rare disease.

What Is Barth Syndrome?

Barth syndrome is a rare disease that is estimated to affect 1 in every 300,000 to 400,000 people, most of whom are males. It affects the mitochondria, often called the “powerhouses of the cell,” which are present in cells throughout your entire body, including in muscles like the heart. Barth syndrome is caused by a change in a gene called tafazzin (TAZ), which affects how your body makes a special fat called cardiolipin. Cardiolipin helps the mitochondria produce energy in the body. When cardiolipin does not work properly, the heart and other muscles, which require a lot of energy to work properly, do not function as well. This can lead to muscle weakness, heart problems, and tiredness.

How Does Forzinity Work to Treat Muscle Weakness in People With Barth Syndrome?

Forzinity works by binding to cardiolipin in mitochondria, helping to restore their normal shape and function so they can produce energy more efficiently. By improving energy production in muscle cells, Forzinity may help ease muscle weakness and tiredness in people with Barth syndrome.

How Do I Use Forzinity?

Forzinity is given as an injection under the skin (subcutaneous) once daily, at the same time each day. It can be given by a health care provider, a trained caregiver, or by yourself once you’ve learned how to do it safely. Forzinity is injected under the skin, into the belly (abdomen) — at least 2 inches away from your belly button — or into the outer area of your thigh. You should “rotate” injection sites each time you use Forzinity. This means that you should inject Forzinity into a different area of the abdomen or outer thigh each day. Rotating the injection sites helps prevent skin problems at areas where Forzinity is injected. Do not inject Forzinity into any area where your skin is sore or sensitive, bruised, red, or hard. Also, avoid injecting it into scars or stretch marks. After you have used your dose of Forzinity, make sure to throw away any used needles and syringes in an FDA-approved sharps container. You can find out more about sharps disposal in the state you live in on the FDA website at fda.gov/safesharpsdisposal. If you do not have an FDA-approved sharps disposal container, you can use a household container if it meets all of the following criteria:

• Made out of heavy-duty plastic that needles can’t pierce
• Can be closed with a tight-fitting, puncture-resistant lid
• Remains upright and stable during use
• Leakproof
• Has a warning label on the outside indicating it contains hazardous waste

How Was Forzinity Studied in People With Barth Syndrome?

A clinical study called TAZPOWER was done to test the safety and effectiveness of Forzinity in people with Barth syndrome. To be included in the study, people needed to be at least 12 years old, weigh more than 66 pounds, and not have significant kidney disease. In the first part of the study, people got daily injections of Forzinity 40 mg or a placebo (containing no medicine) under their skin for 12 weeks. Then, after four weeks of no treatment, people were switched to the treatment they did not get during the first treatment period (daily injections of Forzinity or placebo) and continued getting that treatment for 12 weeks. After completing the second treatment period, people could enroll in an extension study for three years, where everyone got a daily injection of Forzinity. Researchers looked at two different tests to see how well Forzinity worked to improve muscle weakness and tiredness.

• Six-minute walk test. This test looks at how far a person can walk in six minutes. It helps health care providers measure endurance, strength, and how well the heart and lungs are working.
• Total fatigue score on the Barth Syndrome Symptom Assessment. The Barth Syndrome Symptom Assessment is a scoring tool that checks how severe your Barth syndrome symptoms are. The total fatigue score is calculated by adding up the scores from responses to specific questions related to symptoms of tiredness.

They also looked at whether muscle strength in the leg muscle used to straighten the knee (called the knee extensor muscle) improved over the entire study period. Increased strength in this muscle may help with everyday activities, such as standing up more easily or walking longer distances.

The extension study looked at how safe and tolerable Forzinity was when taken daily for more than three years.

What did the study population look like?

The TAZPOWER study included 12 males with Barth syndrome. Their ages ranged from 12 to 35 years, with an average age of 19.5 years. The average weight of people was about 112 pounds. One person was multiracial (not defined), and the remaining 11 were White; no one in the study was Hispanic or Latino.

Ten people from the original study went on to participate in the extension study.

What did the study find?

When comparing participants who received Forzinity with those who got a placebo, researchers did not find noticeable differences in the six-minute walk test or the total fatigue score on the Barth Syndrome Symptom Assessment. However, longer-term treatment with Forzinity resulted in stronger muscle strength in the leg muscle used to straighten the knee.

What Should I Know About the Long-Term Effectiveness of Forzinity?

The FDA approved Forzinity through a pathway called “accelerated approval” based on the long-term study results showing that it improved leg muscle strength in people with Barth syndrome. The FDA’s accelerated approval pathway allows for earlier approval of medicines for serious conditions based on early signs showing that they might help offer relief for the condition, even if their full benefit has not been confirmed at the time of approval. For Forzinity to continue to be approved for the treatment of Barth syndrome, the FDA will require another study. This study will confirm whether the improvements in muscle strength seen in the TAZPOWER study equate to benefits for people with Barth syndrome.

How Can I Manage Side Effects?

The most common side effect of Forzinity is redness, itching, or pain at the site where the medicine is injected, also called an injection site reaction. If you have any of these symptoms, it might help to apply a cold compress to the affected area. Over-the-counter medicines, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin), may also help with pain. If you have any bothersome skin problems in the area where you inject Forzinity, talk to your health care provider. They may recommend steroid creams or antihistamines that may help with these symptoms. If you have any symptoms of a more serious allergic reaction after using Forzinity, such as rash, hives, cough, or difficulty breathing, do not use any more doses of the medicine and get emergency help. A serious allergic reaction may happen within minutes of getting a Forzinity dose or even months later.

Getting Your Medicine: What to Expect

The drugmaker estimates that Forzinity will be available to order by December 2025. Once available, you must get Forzinity from a specialty pharmacy called AnovoRx.

There is a patient support program called Mito Assist that can help you train how to use Forzinity at home, as well as with insurance or cost-related issues. You can learn more by calling 833-458-9099.