An Overview of Onpattro

The First Small Interfering Ribonucleic Acid Therapy (siRNA)

In August of 2018, the United States Food and Drug Administration (FDA) fast-tracked the approval of a drug called patisiran, sold under the brand name Onpattro. The treatment is the first in a new class of drugs called small interfering ribonucleic acid therapy (siRNA) to be approved by the FDA.

It's also the first treatment to be approved for patients with hereditary transthyretin-mediated amyloidosis (hATTR), a rare genetic condition in which there is an abnormal buildup of proteins in the organs and tissues. In some cases, this results in a loss of feeling in the extremities.

What Is Onpattro?

Onpattro is a type of RNA interference (RNAi) therapy. RNAi therapy makes use of a process that already occurs in cells at the genetic level. There are two main components of genes: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most people are familiar with DNA, which can be easily recognized by its classic double-stranded (double helix) appearance.

However, there is also single-stranded RNA, which researchers are only beginning to fully understand the importance of, especially when it comes to diseases that are caused by genetic defects passed down through families.

Approved Indications

Onpattro is only approved for use in adult patients with hereditary transthyretin-mediated amyloidosis and polyneuropathy who are still in the early stages of nerve damage (I and II). The medication has not been tested in patients with nerve damage severe enough to require the use of a wheelchair.

About 50,000 people worldwide are known to have hATTR which can cause an array of symptoms in multiple systems in the body. Due to a genetic mutation, a protein produced by the liver called transthyretin (TTR) doesn't do its job the way it should.

People who have hATTR develop symptoms when TTR builds up in their body, forming clusters called amyloid deposits.

Different symptoms which may appear to be unrelated at first arise in various parts of the body due to where the deposits buildup. For example, if TTR builds up in the gastrointestinal system, people develop diarrhea, constipation, and nausea. In the neurologic system, symptoms sometimes appear similar to those of a stroke or dementia. Cardiac disturbances, including potentially life-threatening arrhythmias, are also possible.

Another set of symptoms that afflict many people with hATTR relates to the nerves that control the arms and the legs (peripheral nervous system). When TTR builds up in these nerves, a condition called polyneuropathy can develop. The symptoms of polyneuropathy (including weakness and tingling) can be severe, debilitating, and in some cases life-threatening.

Onpattro has been approved specifically to treat polyneuropathy in patients who have hATTR. The medication is given as a liquid through an intravenous line (IV), a type of drug delivery called infusion. Once it enters the body, the drug goes to the liver where it acts on the production of dysfunctional proteins, shutting it down. When less of the protein is made, ideally the buildup of amyloid deposits will also slow or even stop.

Is Onpattro Safe?

Onpattro works by using a small piece of RNA to disrupt the dysfunctional protein production process in people with hATTR. When introduced into the cell, the RNA delivered by Onpattro can "cut" the mRNA that has the instructions for producing the protein. By silencing the gene, those instructions stop being sent.

In clinical trials for the drug, patients were given one infusion of Onpattro every three weeks for 18 months. Patients who received treatment saw an improvement in polyneuropathy symptoms. Patients who received no medication (a placebo dose) did not see an improvement, and in some cases, nerve damage continued to worsen.

Side Effects

Some patients reported side effects of infusion therapy, including flushing, nausea, and headache. Other medications, such as steroids and antihistamines, can be given to reduce the risk of infusion-related side effects.

Colds, sinus infections, and upper respiratory illness were also reported by some patients receiving Onpattro. However, most side effects were not serious and got better over time.

It's important for patients to know that Onpattro can lower levels of Vitamin A. Patients who take Onpattro may also need to take supplemental Vitamin A to avoid deficiency. Signs of Vitamin A deficiency typically include visual changes such as night blindness.

Dosage

How much Onpattro is prescribed will depend on how much a patient weighs. Most adult patients will receive approximately .3 mg/kg of body weight by infusion every three weeks. Each infusion takes approximately 80 minutes to complete. The amount, frequency, and duration of infusions may be altered depending on how a patient responds, if their health changes, or if they experience side effects.

Infusions usually take place in a hospital or other medical facility where staff can prepare the medication, administer it, and monitor patients during and after the infusion. Some patients will be allowed to have infusions at home with help, such as from a visiting nurse after they have had several successful infusions in the hospital.

Contraindications

There are no known drug contraindications for Onpattro. Data from the clinical trials did not specifically focus on potential drug interactions, but researchers believe it is safe to take Onpattro with most other commonly prescribed medications. Patients should always tell their doctor about any medications or supplements they are taking, even if they are over-the-counter.

More research is needed to assess the safety of using Onpattro in patients who are pregnant or breastfeeding. The medication has been studied and approved for adults. It appears to work as well in men as it does in women. The majority of the patients in the clinical trial were white males. More research is needed to determine if there are any differences in the drug's effectiveness in other patient populations.

All of the patients in the clinical trial were adults and Onpattro is only approved for use in adult patients. The use of Onpattro has not been studied in children.

In 2018, the cost to treat one patient with Onpattro was estimated to be $450,000 per year.

Alnylam, the manufacturer of Onpattro, and other pharmaceutical companies are working on more drugs using RNAi therapy.

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