Focal segmental glomerulosclerosis (FSGS) is a long-term condition where scar tissue forms in your kidneys. People with small amounts of scar tissue may not have any symptoms at all. Proteinuria (leaking protein from your blood into your urine) can happen as FSGS worsens. Proteinuria can cause more kidney damage. Eventually, some people with FSGS will have more serious kidney damage leading to nephrotic syndrome, kidney failure, or the need for a kidney transplant.
There are limited treatment options available for FSGS. In April 2026, the FDA approved Filspari (sparsentan), the first specific treatment option to reduce urine protein levels in people with FSGS before it progresses to nephrotic syndrome.
Continue reading to learn more about the benefits of taking Filspari, how it works, and what to expect with use.
You may also want to read about Filspari side effects and Filspari interactions.
How Does Filspari Work for FSGS?
Your kidneys’ number one job is to “clean” your blood. It does this with tiny filters in your kidneys, called glomeruli. In people with FSGS, scar tissue forms in at least some of your glomeruli, making it hard for your kidneys to do their job.
Endothelin-1 and angiotensin II are hormones in your body involved in regulating blood pressure and kidney function. These hormones seem to be overly active in certain conditions such as FSGS and may play a role in kidney damage. Filspari blocks two specific targets in your body where endothelin-1 and angiotensin II work. This seems to help protect the filters in your kidneys and reduce the amount of protein that leaks into urine.
How Do I Take Filspari for FSGS?
Filspari is a tablet that you take once a day, around the same time each day, either before your morning or evening meal. You should be consistent and take it before the same meal every day.
For treating FSGS, your starting dose will be based on your weight. If you weigh 50 kg (around 110 pounds) or less, you will likely start with 200 mg once a day. If you weigh more than 50 kg, or more than 110 pounds, your starting dose will likely be 400 mg once a day. Starting doses are usually taken for the first 14 days. Then you will likely double your starting dose and take the higher dose from that point forward.
Note that these instructions are based on standard dosing guidance for Filspari. You should not change your dose without your health care provider telling you to do so. Always follow the instructions from your health care provider, which may be different for your specific situation. Ask your pharmacist or health care provider if you have questions about how to take Filspari.
If you have trouble swallowing Filspari tablets, you can mix them with water to make it easier. Consider the following steps for it.
- Crush your tablet (using a pill crusher or mortar and pestle).
- Mix the crushed tablet in 1/2 cup of water (Note: It will not dissolve).
- Drink the water and tablet mixture right away. Do not save it for later.
- Add a little bit more water to the container if there are any small pieces of tablet left in the container. Swirl the water around and drink all of it.
If you miss a dose, skip the missed dose. Just take your next dose when you normally would. Do not take double or extra doses to make up for a missed dose.
If you have any questions about how to take Filspari, talk to your pharmacist or health care provider.
How Was Filspari Studied for FSGS?
Researchers studied how well Filspari worked in children and adults with FSGS in one clinical trial. In this study, people were randomly assigned to receive either Filspari or irbesartan. Irbesartan is an angiotensin II receptor blocker (ARB), which is a medicine for high blood pressure, heart failure, other heart conditions, and kidney problems. Neither the participants nor the researchers knew who was receiving which treatment.
People who had previously had a kidney transplant or had taken certain medicines within the last three months, such as abatacept, cyclophosphamide, or rituximab, were not able to participate in the study. People taking other medicines that affect the immune system, such as azathioprine, calcineurin inhibitors (cyclosporine or tacrolimus), mycophenolate mofetil, or steroids, had to be on a stable dose for at least one month before they could join the study.
People taking certain medicines had to stop taking them two weeks before they could start taking the study medicine.
Here are a couple of terms and definitions you should be familiar with in order to better understand how Filspari was studied.
- Estimated glomerular filtration rate (eGFR) predicts how much blood, in milliliters (mL), your kidneys can filter each minute. It is calculated using a lab test, your age, and sex. In general, the higher the number, the better job your kidneys are doing at filtering your blood. An eGFR of 90 mL/min/1.73 m2 or higher is considered normal kidney function. As kidney function gets worse, eGFR goes down, meaning your kidneys are not as good at filtering your blood.
- Urine protein-creatinine ratio (UPCR) compares the amount of protein in your urine (in grams) to the amount of creatinine in your blood (also in grams). In general, lower is better, meaning more protein is staying in your blood, and less protein is leaking into your urine. A normal UPCR is usually less than 150 mg/g or 0.15 g/g.
The people in this study had the following characteristics when the study started.
- The average age was 42 years; ages ranged from 9 to 75 years.
- Just over half of the participants were male (54%); the rest were female (46%).
- 73% were White, 13% Asian, 7% Black or African American, and 7% identified as being of other, multiple, or unknown race.
- The average eGFR was 63 mL/min/1.73 m2.
- The average UPCR was 3.1 g/g.
The main goal of the study was to evaluate the rate of change in kidney function using eGFR over 108 weeks (around two years). The study also looked at changes in urine protein levels over this same time frame.
What Benefits Were Seen?
The change in eGFR from the beginning to the end of the study was not significantly different for people who took Filspari compared to those who took irbesartan. Kidney function seemed to continue to change in both groups at about the same rate.
While Filspari did not slow the rate of kidney function decline compared to irbesartan, it did show a benefit in reducing urine protein levels, especially in people without nephrotic syndrome.
The table below shows how much urine protein levels changed during the study for each treatment group.
All study participants | People without | People with | ||||
|---|---|---|---|---|---|---|
Filspari (184 people) | Irbesartan (187 people) | Filspari (129 people) | Irbesartan (125 people) | Filspari (55 people) | Irbesartan (62 people) | |
| Percent reduction in UPCR at two years | 46% | 30% | 48% | 27% | 39% | 37% |
| Average difference from Irbesartan | 22% | 29% | 3% | |||
In people who did not have nephrotic syndrome at the start of the study, Filspari did a better job than irbesartan at reducing urine protein levels. After about two years of treatment, people taking Filspari had a significantly greater drop in their urine protein levels than people taking irbesartan.
Keep in mind that your results may differ from what was seen in this study.
How Long Does It Take for Filspari to Work?
Filspari seems to start working fairly quickly. In the study discussed above, there was a noticeable lowering of urine protein levels (especially in people without nephrotic syndrome) as early as about six weeks after starting the medicine. Urine protein levels seemed to stay at this lower level throughout the rest of the two-year study.
What to Expect When Getting Your Medicine
Filspari is part of the FDA Risk Evaluation and Mitigation Strategy (REMS) program. This program is required by the FDA for certain medicines. The Filspari REMS program helps make sure you and your health care provider are informed about how to take Filspari safely, including monitoring your liver function with regular blood tests.
As part of this REMS program, your health care provider will discuss the risks of liver damage with you. You will also need to have regular blood tests done to see how well your liver is working before and while taking Filspari. You can learn more about the Filspari REMS program by visiting this website or calling 833-513-1325.
Is There Any Assistance Available?
Yes. The drugmaker of Filspari offers a support program, Travere TotalCare, to help patients and caregivers during treatment with Filspari. Below are the examples of how you can benefit from this program:
- Direct phone number to reach a nurse
- Help getting started and staying on track with your Filspari treatment
- Help with receiving your Filspari refills
- Information about cost savings opportunities that may be available
- Communication and updates about Filspari by text, phone, or email
You can find out more information and enroll in Travere TotalCare by going to this website or calling 833-FILSPARI (833-345-7727).
What Other Considerations Should I Be Aware Of?
Filspari can be harmful to a fetus. If there is any chance you can get pregnant, your health care provider will do a pregnancy test before you start this medicine and talk with you about your birth control options. It is important to use an effective form of birth control before starting Filspari, while you are taking it, and for two weeks after your last dose. If you find out you are pregnant while taking Filspari, stop taking it right away and call your health care provider.