The purpose of this clinical trial is to find out whether an investigational medication, givosiran, can prevent or reduce attacks and symptoms associated with porphyria. It is also looking to better understand the safety of givosiran and how the how the body responds to it.

Who is eligible for ENVISION?

The ENVISION trial is for people who:

  • Have a confirmed diagnosis of AIP, HCP, VP, or ADP
  • Have had at least 2 porphyria attacks in the past 6 months that required either:
    • Hospitalization, or
    • Urgent healthcare visit*, or
    • Treatment with hemin at home
  • * Urgent healthcare visits are urgent, unscheduled office/practice visits, infusion center visits, or emergency department visits that do not require hospitalization

To find out if you are eligible to participate in ENVISION some information from your medical records will be needed and additional tests will be performed.

Will everyone get the investigational medication?

For the first 6 months of the trial, participants will be randomly assigned to 1 of 2 groups:

  • Investigational medication: There is a 50% chance of being assigned to this group
  • Placebo: There is a 50% chance of being assigned to this group.

A placebo looks just like the investigational medication but does not contain any active ingredients.

If participants have an attack during the study, they will be able to take hemin (if available).

Neither participants nor the study team will be able to choose which group they are assigned to. In addition, neither of them will know if they are assigned to receive the investigational medication or the placebo. This is called double-blind.

In both groups, the study medication is given as a subcutaneous injection (just under the skin). After completing the 6-month double-blind treatment period, participants will enter the open-label extension (OLE) period where all participants will receive monthly injections of the investigational medication for up to 30 months (2.5 years).

What about my usual porphyria attack treatments?

ENVISION participants will be instructed by the study doctor on how to treat any attacks that occur during the trial. The study doctor will also discuss how to manage any chronic symptoms that may be experienced, including pain.

Participants who currently take hemin on a regular basis to prevent attacks (prophylaxis usage) will need to stop taking it when they enter screening. This is to allow the researchers to see the effects of the investigational medication. It ensures that any effects that could otherwise be due to taking hemin are not attributed to the investigational medication.

How long does the ENVISION study last?

Participation in ENVISION will last up to approximately 38 months.

(1-2 visits)

up to 2 months

To check eligibility for the trial

Double-Blind Treatment

6 months

Participants will be randomly assigned to 1 of the following treatment groups:


During this time participants will have 8 study visits. There is a 50% chance of receiving the investigational medication and a 50% chance of receiving a placebo, given once a month.

Open-Label Extension (OLE)

Up to 30 months (2.5 years)

During this time participants will have regular study visits. All participants will receive the investigational medication once a month

Will it cost me anything to participate?

The study medication and all trial-related procedures are provided at no cost. In addition, transportation to and from study visits, or reimbursement for travel-related costs may also be provided.

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