Travere Therapeutics, Inc. ($TVTX)

Hello, and welcome to Travere Therapeutics First Quarter 2026 Financial Results Conference Call. Today's call is being recorded. At this time, I would like to turn the conference call over to Nivi Nehra, Vice President, Corporate Communications and Investor Relations. Please go ahead, Nivi.

Thank you, operator. Good afternoon, and welcome to Travere Therapeutics First Quarter 2026 Financial Results and Corporate Update Call. Thank you all for joining. Today's call will be led by Dr. Eric Dube, our President and Chief Executive Officer. Eric will be joined in the prepared remarks by Dr. Jula Inrig, our Chief Medical Officer; Peter Heerma, our Chief Commercial Officer; and Chris Cline, our Chief Financial Officer. Dr. Bill Rote, our Chief Research Officer, will join us for the Q&A. Before we begin, I'd like to remind everyone that statements made during this call regarding matters that are not historical facts are forward-looking statements within the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Forward-looking statements are not guarantees of performance. They involve known and unknown risks, uncertainties and assumptions that may cause actual results, performance and achievements to differ materially from those expressed or implied by the statement. Please see the forward-looking statement disclaimer on the company's press release issued earlier today as well as the Risk Factors section in our Forms 10-Q and 10-K filed with the SEC. In addition, any forward-looking statements represent our views only as of the date such statements are made, May 4, 2026 and Travere specifically disclaims any obligation to update such statements to reflect future information, events or circumstances. With that, let me now turn the call over to Eric. Eric?

Thank you, Nivi. Good afternoon, and thank you for joining us. This has been a tremendous start to the year for Travere. We've made significant progress across our three strategic priorities. We achieved the first FDA approval in FSGS, we reported a new high in demand for FILSPARI in IgA nephropathy, and we dosed the first new patient in the Phase III HARMONY study of pegtibatinase following restart of enrollment. April 13 marked a pivotal point for the FSGS community and Travere. Achieving the first full FDA approval for FILSPARI in FSGS established it as the first and only approved medicine for this rare and devastating kidney condition. With the potential to help more than 30,000 people living with FSGS without nephrotic syndrome, this approval is a significant indication expansion for FILSPARI and meaningfully increases the opportunity ahead for us. The first quarter also marked another period of exceptional commercial performance in IgA nephropathy. We delivered another quarter of record new patient start forms. As we look ahead, we are already building upon our experience gained from the successful launch of FILSPARI in IgA nephropathy and are executing a strong launch in FSGS. Across IgA nephropathy and FSGS, we are now estimating that more than 100,000 patients in the U.S. could be eligible for FILSPARI. Together, we believe this represents a $3 billion potential peak sales opportunity for FILSPARI, reinforcing a compelling long-term growth trajectory for the company. We are also advancing our pipeline to support further sustainable growth. We recently dosed the first new patient in our pivotal Phase III HARMONY study, evaluating pegtibatinase in classical homocystinuria following the restart of enrollment. Importantly, achieving this milestone puts us on track to deliver top line results in the second half of 2027. Based on the data we've generated to date, we believe this program has the potential to become the first disease-modifying therapy for the HCU community. We expect there are approximately 7,000 to 10,000 people living with HCU globally who would be addressable for pegtibatinase. I'm incredibly proud of our team's accomplishments and look forward to accelerating Travere's growth as we expand our reach and serve more patients across the rare disease community. With that, I'll turn it over to Jula for a medical update. Jula?

Thank you, Eric. I'm very excited to have the first ever approved medicine for the FSGS community now available for patients. As a reminder, FILSPARI was approved to reduce proteinuria in adults and children 8 years and older with FSGS without nephrotic syndrome. I would like to take a moment to highlight how nephrotic syndrome is defined in clinical practice and what it means in the context of which patients may be eligible for FILSPARI. Nephrotic syndrome is a clinical diagnosis and is typically defined by the presence of all three of the following criteria: high levels of proteinuria greater than 3.5 grams per day, low serum albumin levels of less than 3.0 grams per deciliter and the presence of edema. If a patient is missing any one of these criteria, they are not considered to have active nephrotic syndrome. This is different than nephrotic range proteinuria, which is typically greater than 3.5 grams per day. For example, a patient with 4 grams of proteinuria, low serum albumin but no edema will be eligible for FILSPARI. Importantly, nephrotic syndrome is not a chronic state as a patient with FSGS presents without nephrotic syndrome, which represents the majority of the FSGS population spanning all types of FSGS. They are immediately available for FILSPARI. For those who initially present with nephrotic syndrome, physicians will typically use immunosuppression induction to try to control the patient's proteinuria and stabilize them after which these patients may also become eligible for FILSPARI. In addition, based on the data from DUPLEX, patients treated with FILSPARI demonstrated sustained reductions in proteinuria over time with proteinuria levels reaching approximately 1.5 grams per gram or less on average at study end. At these proteinuria levels, patients would be expected to have a much lower risk of relapsing to nephrotic syndrome. Based on our discussions with key opinion leaders following the approval, there is wide enthusiasm for using FILSPARI across the types of FSGS, including among secondary and genetic FSGS. This is supported by our recent publication in [ C JSON ], demonstrating consistent efficacy and safety in patients with genetic FSGS, a population often considered the most difficult to treat. Physicians consistently highlight the need for effective non-immunosuppressive options for long-term disease management. Now let me talk about IgA nephropathy. We recently published data in [ C JSON ] from the PROTECT study, showing that patients with IgA nephropathy who achieved complete remission of proteinuria to less than 0.3 grams per gram experienced rates of eGFR decline of less than 1 milliliter per minute per year, a rate which is similar to healthy aging. The KDIGO guidelines recommend a treatment approach for IgA nephropathy that addresses both kidney injury and upstream immune drivers and include FILSPARI as a first-line option for patients at risk of progression. The data published this month reinforce FILSPARI's role as a foundational medicine in IgA nephropathy, demonstrating that FILSPARI helps more patients reach complete remission, which is associated with improved preservation of kidney function over time. Turning briefly to our pipeline. We are pleased to have reinitiated enrollment in our Phase III HARMONY study of pegtibatinase with the first new patient now dosed. HARMONY is a randomized double-blind study designed to evaluate the efficacy and safety of pegtibatinase compared to placebo with the primary endpoint focused on reduction in plasma total homocysteine, a key driver of disease in classical HCU. The primary endpoint for HARMONY is assessed at 12 weeks, consistent with the primary endpoint timing from our Phase I/II COMPOSE study. Patients who complete the HARMONY study are eligible to enroll in the ENSEMBLE extension study. This open-label extension will allow us to evaluate long-term outcomes, including sustained homocysteine control as well as meaningful aspects for patients such as the potential for greater dietary flexibility and self-administration. This program is supported by data from our Phase I/II COMPOSE study, where pegtibatinase demonstrated rapid, sustained and dose-dependent reductions in total homocysteine levels. At the 2.5 milligram per kilogram dose twice a week, pegtibatinase delivered a 67.1% mean relative reduction in total homocysteine from baseline to 12 weeks as well as maintenance of mean total homocysteine below the clinically meaningful threshold of 100 micromoles and was generally well tolerated. pegtibatinase has the potential to become the first disease-modifying therapy for patients living with classical HCU, and as Eric mentioned earlier, we expect top line data from the HARMONY study in the second half of 2027. Finally, we continue to generate and share new data across IgA nephropathy, FSGS and HCU, and we look forward to upcoming medical meetings, including NKF this week and ERA next month, where we will present additional analyses in both IgAN and FSGS. I'll now turn it over to Peter for a commercial update. Peter?

Thank you, Jula. I'm pleased to share that we started the year strongly and set new records with our FILSPARI performance. The first quarter marked the highest demand to date as we received 993 new patient [ start forms ], reflecting continued expansion among new prescribers and deepening utilization across established accounts. Importantly, we continue to see an increasing number of practices treating multiple IgA nephropathy patients with FILSPARI with [ VVO ] as a meaningful indicator of physicians' confidence with the medicine's foundational and nephroprotective positioning. As new treatment options become available for this indication, FILSPARI remains the most commonly prescribed medicine approved for IgA nephropathy in the U.S. This broad utilization supports our confidence in FILSPARI's continued growth potential in IgAN, and we are seeing strong demand in the start of the second quarter. For the first quarter of 2026, we reported approximately $105 million in FILSPARI revenue despite the typical beginning of the year insurance resets and gross to net dynamics as well as recognizing fewer revenue shipping weeks. The strength of our performance in IgAN and the momentum we have with FILSPARI is directly relevant as we enter the FSGS launch. There is significant overlap in the prescriber base between these two indications, and many nephrologists already have experience with FILSPARI in their IgAN patients. This will support early adoption in FSGS patients, and we anticipate a faster uptake compared to the initial IgAN launch. In fact, early feedback from the FSGS community has been overwhelmingly positive. We received our first patient start forms already on the first day following approval, and we are encouraged by the enthusiasm and engagement we are experiencing. Having spent time in the field over the past 2 weeks, I have seen that enthusiasm firsthand in discussions with nephrologists in their offices, and it reinforces our belief that the FSGS opportunity is expected to be even bigger than IgA nephropathy. Established payer access in IgAN is helping to position FILSPARI for a supportive access environment in FSGS. In fact, we saw our first FSGS reimbursement approvals already in the first week. Payers often manage access at the product and indication level, and our team is focused on expanding payer plans and formularies to include FILSPARI or FSGS. While education on the FSGS indication will be important, we are starting from a position of strength with an experienced commercial team and an established infrastructure. We believe there are more than 30,000 patients in the U.S. with FSGS who are currently eligible for FILSPARI, and we expect that number to grow. In summary, the start of 2026 reflects exceptional commercial execution with record demand and revenue growth. With our continuing performance in IgA nephropathy and FILSPARI recent FSGS approval, I am confident in our ability to continue to delivering strong, sustained growth and long-term leadership across these rare kidney disease indications. I am incredibly proud of our team and the impact they continue to have on patients and physicians, and I'm excited for what lies ahead for us in 2026. I'll now turn the call over to Chris for the financial update. Chris?

Thank you, Peter. As you've heard from the team, we delivered another strong quarter of execution across the business and, recently, we achieved an important milestone with FILSPARI's approval in FSGS that further strengthens our outlook for continued growth. In the first quarter, we generated $124.5 million in total U.S. net product sales, reflecting strong year-over-year growth. Importantly, U.S. net product sales of FILSPARI grew approximately 88% year-over-year to $105.2 million despite typical beginning of year gross net impact and fewer revenue recognition days. As Peter noted, for FILSPARI, we recognize revenue when product is delivered to our specialty pharmacies. This typically occurs a couple of days after shipment from our logistics partner. Due to the quarter end timing and typical early week ordering patterns, the first quarter had 1 fewer shipping weeks than usual. As a result, some FILSPARI shipments made in the first quarter will be recognized in the second quarter. Adjusting for this dynamic and supported by record demand during the first quarter, we believe FILSPARI is on a strong trajectory in IgA nephropathy for the balance of the year. Elsewhere, THIOLA and THIOLA EC contributed $19.3 million in U.S. net product sales during the first quarter, and we recognized $2.7 million in license and collaboration revenue resulting in $127.2 million in total revenue for the first quarter. Moving to operating expenses. Our research and development expenses for the first quarter of 2026 were $57.1 million compared to $46.9 million for the same period in 2025. On a non-GAAP adjusted basis, R&D expenses were [ $51.5 million ] compared to $42.2 million for the same period in 2025. The increase is primarily driven by the restart of enrollment in the Phase III HARMONY study of pegtibatinase during the quarter. Selling, general and administrative expenses for the first quarter of 2026 were $80.3 million compared to $60.4 million for the same period in 2025. On a non-GAAP adjusted basis, SG&A expenses were $69.3 million compared to $53.3 million for the same period in 2025. The increase is primarily attributable to investments in preparation for FILSPARI's launch in FSGS, including an expanded field team as well as investments in IgA nephropathy. Beginning in the first quarter, we revised the presentation of our amortization expense associated with royalty and milestone payments to a separate royalty expense line item in order to provide greater transparency to underlying operating expenses. For the quarter, we recognized $24.8 million in royalty expense compared to $12.4 million for the same period in 2025. The increase is primarily a result of the THIOLA intangible asset reaching the end of its accounting useful life, resulting in amortization of the full amount of the royalty payments accrued this quarter as well as an increase in capitalized FILSPARI royalties. Under accounting policy, THIOLA royalties will now be expensed to royalty expense in the same quarter as a corresponding net sales. Contractual milestones and royalty payments related to FILSPARI will continue to be capitalized to intangible assets and amortized on a straight-line basis over its useful life with only amortized expense recognized within royalty expense. Total other income net for the first quarter 2026 was less than $1 million compared to $1.5 million for the same period in 2025. Net loss for the first quarter of 2026 was $37.1 million or $0.40 per basic share compared to a net loss of $41.2 million or $0.47 per basic share for the same period in 2025. On a non-GAAP adjusted basis, net income for the first quarter was $4.1 million or $0.05 per basic share compared to a net loss of $16.9 million or $0.19 per basic share for the same period in 2025. As of March 31, 2026, we have cash, cash equivalents, marketable securities and receivables of approximately $352 million. Receivables include the $25 million sales-based milestone payment from Mirum Pharmaceuticals that was recognized in the fourth quarter of 2025 and received in April. This is not yet reflected in our cash balance of approximately $264.7 million as of March 31. Looking ahead, we are well positioned to fund our operations with existing resources. We're investing with discipline across our key priorities, including the commercialization of FILSPARI in IgA nephropathy and FSGS, ongoing evidence generation and advancement of the pivotal HARMONY study of pegtibatinase in HCU, alongside building further pegtibatinase supply. We expect continued strong demand in IgA nephropathy to drive sustained revenue growth, with FSGS further contributing to our top line trajectory. Overall, we believe our balance sheet, expected top line expansion and disciplined approach to investing in our priorities position us to execute with confidence and deliver durable long-term growth. I'll now turn the call over to Eric for his closing remarks. Eric?

Thank you, Chris. As we look ahead, our priorities are clear: continue to drive growth by reaching more patients with IgA nephropathy, execute a strong launch in FSGS and enroll our HARMONY study of pegtibatinase. With FILSPARI now approved in IgA nephropathy and FSGS and a pipeline progressing into late-stage development, we believe we are well positioned to deliver meaningful value for patients and shareholders over the near and long term. With that, I'll turn the call back over to Nivi for Q&A. Nivi?

Thank you, Eric. Operator, we can now open up the line for Q&A.

[Operator Instructions] Your first question comes from the line of Joseph Schwartz with Leerink Partners.

This is Will Soghikian on for Joe. Congrats on all the progress this quarter. The one for us on FSGS, you guys have messaged several times that the launch is expected to progress at a faster rate than IgA nephropathy. Could you please characterize what you're seeing at this early stage and how it compares to the original IgAN rollout a few years ago? It seems like the full approval here could also make a difference, especially since we know nephrologists are sometimes slower to adopt innovative medicines. Is what you're seeing in these early days supportive of a more rapid FSGS launch?

Will, thank you so much for the question. And I am very pleased with the early performance and particularly the execution from our field teams. Peter, with that, why don't you give some color to what you are seeing in the early part of the launch?

Absolutely, Eric. And Will, thank you for that question. And indeed, we are confident in a faster uptake in FSGS relative to the IgAN launch for multiple reasons. First of all, this is a very high unmet need and this is the fastest progressive glomerular disease as well where, for IgAN, we really had to establish the urgency to intervene earlier. In addition to that, we built upon a very strong brand awareness and many of the physicians already have the experience with FILSPARI given this is basically the same core point for IgA nephropathy. And from a payer perspective, we already are in most of the formularies and payer plans. We have currently over 97% pathway to access for patients. So we built upon a very strong foundation, and that gives me confidence that we will have a more rapid uptake in FSGS as relative to our initial IgAN launch, and we believe it's an even bigger opportunity with FSGS than IgAN.

Your next question comes from the line of Tyler Van Buren with TD Cowen.

This is [ Greg ] on for Tyler. So you noted that the first FSGS PSFs arrives the day after approval and reimbursed treatment started within 1 week. So how many FSGS PSFs have you recorded thus far in the launch? And what proportion of early starts are coming through payer authorizations versus exceptions or appeals? And what are you seeing on initial payer behavior in general?

[ Greg ], thanks so much for the question. While it's too early for us to be able to quantify some of that, Peter certainly can provide some qualitative and directional views on the demand and the payer dynamics. Peter?

Yes. Greg, I would love to answer that question. But this is a Q1 call, so I'm looking forward to share that with you in the second quarter call. But following my answer on the earlier question on the faster uptake in IgA nephropathy, I would say everything we are seeing so far is confirming what I have said with regards to a faster uptake than our initial IgA nephropathy launch. That accounts both for demand as well as for the early approval rates that we are seeing with payers. We're seeing actually a higher first pass approval at the payer level than what we saw initially for IgAN.

Your next question comes from the line of Anupam Rama with JPMorgan.

I was wondering on the FSGS launch if you could build upon some of your prior comments, which was I know you mentioned that there is a need to further educate physicians. I know that it's only 3 weeks post approval. But I was wondering if you could speak to what's resonating with physicians in terms of the label and the product profile. And then within that, where do you think the education is required?

Anupam, thanks so much for the questions. Peter, why don't you take that? And Jula, I know your team has got extensive engagements with thought leaders, so you can add anything that you might want to. Peter?

Yes. Happy to take that question, Anupam. And to my earlier point, overwhelmingly positive responses from the physicians, but you still have to educate them. You still have to [ read ] to them. I was in the field a few days, and many of the community nephrologists in particular, they may not know yet that FILSPARI was approved. And so that awareness, you have to build. You have to educate physicians also on the label, in particular, with like not being a nephrotic syndrome. That requires some education. Once you explain that, it resonates with physicians because it's very similar to how patients are being treated today. It's actually very consistent also to the guidelines, KDIGO guidelines. But maybe Jula can provide some further context on that.

Yes. Thanks. Our team, as Eric mentioned, has been out at conferences, advisory boards, seminars, and I would say that the approval is getting resoundingly positive feedback from physicians. This patient community has been waiting a long time and they are excited to have a non-immunosuppressive treatment option to control these patients and get their proteinuria down. You did ask about education. Part of it is a reminder about active nephrotic syndrome is not the same as nephrotic range proteinuria. So we are educating around that. But as Peter mentioned, very positive and excitement to have this option to treat their patients.

Your next question comes from the line of Prakhar Agrawal with Cantor Fitzgerald.

So maybe going back to your comments on faster uptake than IgAN. When I go back to the IgAN launch, in the first few full quarters, you had 400 to 450 patient start forms. Is that how should we think about the uptake for FSGS as well? And secondly, on access. Do you expect payers to cover the secondary FSGS patients broadly as well despite the segment not being tested in Phase III? Are you hearing any pushback from the payers?

Prakhar, thanks for the questions. With regard to the uptake, we're not going to be providing guidance and we won't be breaking out the PSFs by indication as we move forward. I will reinforce what Peter shared that everything that we're seeing so far in the first 3 weeks of launch have confirmed what we've been saying around a faster uptake around an eagerness to prescribe. And the payer dynamics really, I think, help in getting patients from PSFs on to therapy. With that said, Peter, why don't you take the question around payer access and the different types of FSGS, secondary, et cetera, and any pushback, if any?

Yes. No, absolutely. And maybe good to start with repeating what I just mentioned that I'm mostly encouraged by the early approval rates that we are seeing for FSGS, that it's higher than what we saw initially for IgA nephropathy. Before I specifically answer the question, maybe it's good to provide a little bit of context that payers understand that FSGS is a more rare disease compared to IgA nephropathy with a more progressive nature. This is what we have been educating payers on over the last 6, 7 months. And in that context, payers are not really focused on like types or subtypes of FSGS. They understand the common injury pathway and how FILSPARI is the first approved medicine for this patient population that is rapidly progressing. So that's what I would say what we are hearing and seeing so far in the context of conversations we have had with payers over the last 6, 7 months.

Your next question comes from the line of Vamil Divan with Guggenheim Securities.

I wanted to just get back the topic around [ the history ] in nephrotic syndrome. I think as we've spoken to some physicians since the approval, there seems to be some confusion about this and if they can prescribe FILSPARI in these patients or not. So I'm just curious maybe you can elaborate there in terms of do you think will payers, physicians focus on you if its history in nephrotic syndrome. And it sounds like maybe you mentioned that maybe educations do need to work on, on that topic. So maybe just elaborate on that in terms of what you're doing to make sure it's clear because it certainly sounds like from your perspective that this should not be a limiting factor.

Thank you, Vamil, for the question. And we firmly believe that this is not going to be a challenge. It's certainly an opportunity to educate. Jula, why don't you talk about the efforts that you're doing and the reaction from nephrologists? Peter, you can talk about how payers may be thinking about this topic.

Yes. This has not been an area of focus from physicians, and we've had a fair bit of engagement and so has Peter's team. So we do not believe that history of nephrotic syndrome should reserve a physician from prescribing FILSPARI. And really, the reason for that is because of our labeled indication. It's for patients without active nephrotic syndrome. And this is very much aligned with KDIGO who recommends patients with active nephrotic syndrome be treated with immunosuppression, while those without it, receive optimized supportive foundational care. And that's where FILSPARI provides the best treatment option for these patients.

And happy to build upon that from a payer perspective. And maybe just to build on what I just mentioned with regards to a more rare disease with a more rapidly progressive disease manifestation. The most important one is to educate payers on that what Jula said. Nephrotic syndrome is a dynamic state. It's not like a chronic state. And payers understand that. These conversations haven't really come up given what I said earlier. This is a rapid progressing disease and payers understand that as well.

Your next question comes from the line of Gavin Clark-Gartner with Evercore.

Actually wanted to pivot over to IgA nephropathy quickly. What are you seeing as a discontinuation rates over time here, let's say, maybe at the 1-year mark and the 2-year mark since patients are in therapy? And how does that actually compare to what you saw in the IgAN Phase III?

All right. Peter, why don't you take that question?

Yes. The compliance and the persistence rate for FILSPARI in IgA nephropathy has been very high. We haven't given specifics on the numbers, but we haven't seen any change or disruption in those rates as well, which gives me high confidence both on the effect it has for patients that they're being helped with it, but also the physicians that they are seeing that this product works for a patient population that historically didn't have a treatment option. Jula, maybe you can provide the context what we are seeing versus what we saw in the PROTECT trial.

Yes. I would say consistent. We saw a fairly high persistence of patients staying on treatment during the 2-year double-blind trial, and I think it's very aligned with what we're seeing commercially. And part of the reason for that is patients have that positive reinforcement. Their proteinuria goes down, they see it, and they feel like they're getting better and with very consistent side effect profile to irbesartan. And so patients tend to stay on therapy, and they understand this should be truly a lifelong -- as long as they keep their kidneys, they should stay on FILSPARI.

Your next question comes from the line of Mohit Bansal with Wells Fargo.

This is Sadia Rahman on for Mohit. So the patient start form number this quarter, again, looks very impressive. Can you provide some color on the conversion rate for these forms to patients ultimately starting treatment? And any reason for any drop-offs along the way?

Thanks, Sadia. Peter, why don't you take that?

Yes. I'm glad that you reflect on the 993 patient start forms as impressive because I'm really impressed with my team that is continuing to show growth in IgA nephropathy in a rapidly [ paced ] environment. With regard to conversion, I would say we continue to convert those patients quite rapidly over time. We continue to make improvements with where we are right now that is not as dramatic as what you saw in the beginning. But we don't see any drop-offs or changes. And I think with regards to translation, patient start forms into revenue, that may be part of your question, I think Chris was providing some color on that with regards to less ordering shipment weeks in Q1 relative to also having the typical gross to net dynamics that you see usually in Q1. I hope that I answered your question, Sadia.

Your next question comes from the line of Laura Chico with Wedbush Securities.

I apologize if this has been asked already, but one question I had was on IgA nephropathy dynamics for FILSPARI. It's great to see the PSF number continuing to increase, and I'm presuming that's predominantly from IgA nephropathy patients. But we also had a competitive update Novartis indicated the ALIGN confirmatory study for Vanrafia did not reach statistical significance. And while they will pursue an FDA approval, full approval, I'm just wondering how that changes your views on the competitive landscape dynamics for IgA nephropathy with FILSPARI. How are you thinking about pushes and pulls on demand drivers in '26? And then I have a quick follow-up, if that's okay.

Okay. Peter, why don't you take that? And certainly, Jula, add anything further as you see the evolution or consistency of the treatment landscape.

Yes. I'm happy to answer that question. I think most important, that this is a market in development. Most growth in this marketplace is not coming from competitive share but mainly from continuation of growing the market, and that's exactly what we see. That what we were anticipating. I think FILSPARI is very well positioned to continue to grow in this marketplace because it's really replacing RAS. There is no other product that has that ability to do so. Most competition is in the other sector more immune-suppressive agents, where the B cells are now playing together with the component inhibitors and historically steroids. What I would say physicians understand the positioning of FILSPARI as the foundational nephroprotective treatment option and understand also FILSPARI's positioning relative to atrasentan.

And just one thing, Laura, before you get to your next question. You had asked about the PSF increase. That is all based in Q1, so that would be IgA nephropathy before the approval of FSGS. So we do expect to see an acceleration of the demand over time as we look at both indications. But that's a very, very solid number of 993 patient start forms in Q1, reflects our performance in an increasingly landscape of multiple treatment options. So I think it's a really impressive number that Peter's team has been able to deliver. And why don't you go to your next question, Laura?

Yes. Just real quick. So we've got a few weeks in April with the FSGS approval. It does seem like a couple of PSFs are coming through here. Just out of curiosity, are these originating from existing FILSPARI IgAN or versus kind of newly activated FILSPARI prescribers? And I'm just kind of curious, should we be presuming these are already established prescribers in these early days and these early quarters of launch?

L:aura, thanks so much for the question. It is early. Peter, why don't you comment on what you're seeing thus far?

Yes. It's indeed early. We see both, to be honest, and more color to come in the Q2 call. But I think in this context, it's good to talk about the halo effect. I've spoken about the halo effect in the past and halo effect from the experienced prescribers for IgAN that now also adopt FILSPARI for FSGS. But vice versa, we're starting to hear anecdotes as well from physicians that have been on the fence are excited about starting for FSGS and, based on that, now are also excited to start prescribing an IgAN. So I think a halo effect will benefit both indications.

Your next question comes from the line of Maury Raycroft with Jefferies.

Congrats on the quarter. Maybe following up on Laura's question, focusing on PSFs. I'm trying to think about how to estimate that going forward for IgAN. And you talked about atrasentan as a competitor, but Otsuka also had a good quarter for PSFs growth in IgAN. And so I'm wondering if you have any perspective in how Otsuka is launching their drug and how are you factoring that into your estimates, and if there's any more perspective you can offer and just switching to biologics and how you're thinking about that in your total estimate for $3 billion in peak sales.

Okay. Let me take a couple of those. And Peter, why don't you comment on what you're seeing from a competitive standpoint and switching? The first is that the PSFs moving forward will provide an aggregate. So I recognize, Maury, what you're probably trying to figure out is what in IgAN alone. What I would say is there's no reason to believe we can't continue this level of performance because of the number of patients out there and the very unique positioning that non-immunosuppressive kidney-targeted therapies are, which Peter can speak to. With regard to the peak year sales of $3 billion, that really is based on continued growth in both indications. And we've talked about FSGS being a larger opportunity than IgA nephropathy. So we fully expect there to be growth in both, but a much faster uptake in FSGS is going to allow us to really reach more of those patients over time and contribute more meaningful to growth at peak. What I would say is that we really don't see the dynamics as taking away from our opportunity or performance. But Peter, why don't you talk about that in the context of new patients as well as switches?

Yes. Maury, I think the most important one is that we don't see B-cell as a direct competitor for FILSPARI. I think conceptually, the way patients are being treated for IgA nephropathy is how it was done in the past with RAS inhibition and, on top of that, you use steroids when needed. That concept is now changing well for us in PSFs and FILSPARI as a superior option for those patients. And for those patients that need additional treatment, you have now B-cells as potentially replacing steroids. The growth in this market is not so much competitive growth. It's really like developing the market. This is a highly underdeveloped market historically. There are still so many patients that are treated with generic RAS inhibitors and generic steroids. You have better options available right now. The KDIGO guideline is reinforcing that. I think you have a more ambitious treatment target nowadays. So that requires often more combination therapy as well. So I think there is space for multiple products to grow. And I think FILSPARI is very well positioned in that nephroprotective foundational treatment category.

Yes. Thank you, Peter. And Maury, maybe if we just take a step back. One of the things that I'd like to reinforce is we talked over the last couple of years around the new entrants coming and really helping to accelerate growth within the IgA nephropathy market. That is not going to take away our performance and our outlook. That's exactly what we're seeing with the entrants that have come to the IgA nephropathy foundation. And I think that the performance that we posted this quarter really reflects the opportunity that we have, but perhaps, more importantly, the opportunity that patients that have been undertreated with off-label therapies have the opportunity to really have innovation moving forward, both with FILSPARI as well as the other therapies. And that's really, I think, going to the foundation for continued performance of FILSPARI.

Your next question comes from the line of Jason Zemansky with Bank of America.

Congrats on the progress, Maybe, Jula, one for you. I was curious as to where you get the sense or are seeing FILSPARI's use sequenced in FSGS. Is it in lieu of the ACE/ARBs? Are these patients usually already on SGLT2s? We've just gotten some mixed feedback regarding if this drug is going to be used first line or whether in those, I guess, uncontrolled well already on an ARB and an SGLT2?

Yes. Thanks for the question. So just like IgA nephropathy, the vast majority of patients are already on some form of a RAS inhibitor, an ACE or an arb, even by the time they get sent to the nephrologist, so predating their diagnosis. It's slightly lower than IgA nephropathy because kids may or may not always be on an ACE inhibitor, but you're still talking at more than 70%, at least 80% of patients are on some form of foundational treatment. And as far as SGLT2 inhibitor, I would say it is used, just potentially not quite as prevalent, because we don't have as great of data on SGLT2s. But as Peter has mentioned multiple times, these patients are very high risk for rapid progression to kidney failure. So physicians will be pulling at many things as they can in their tool belt to try and stabilize these patients. And now they have FILSPARI, which is better and head-to-head versus a RAS inhibitor. So they are going to take patients off their RAS inhibitor and initiate FILSPARI and ideally at their next clinic visit when they see these patients.

And Jula, maybe I can add something else for Jason's question. Particularly for those patients with primary FSGS and particularly those with active nephrotic syndrome, they are, based on the guidelines, going to be treated with an immunosuppressant. And once they are not in active nephrotic syndrome, they would be eligible and likely placed on FILSPARI. So in terms of them not being first-line use, it's a slight nuance but that's also an opportunity moving forward. But Jula, please clarify if there's anything further you'd like to add.

No, that's accurate.

Your next question comes from the line of Alex Thompson with Stifel.

Just a quick follow-up question on IgAN and then maybe I'd like to ask about pegtibatinase as well. Maybe, Chris, are you able to quantify the shipping week impact at all? That would be helpful for the quarter. And then for pegtibatinase and the Phase III, congrats on restarting that. Have you met with sort of the FDA review division recently? And how confident are you that total homocysteine is still going to be an approval endpoint here?

All right. Chris, and then we can turn it over to Bill for the pegti question.

Yes. Thanks for the question, Alex. We don't typically break down individual weeks of revenue. So what I would point you to as the best proxy is to take the average for the quarter, we had about 12 weeks of revenue recognition within the quarter, and that will get you to the best proxy there. Bill?

And I will take the pegti question. We've got Breakthrough Therapy Designation for pegti. So that allows us to have a lot of interaction with the FDA. And through that process, we reached alignment on the endpoint for that HARMONY study. And it was noted in the prepared remarks, that mirrors the timing of what we saw in the COMPOSE study. So it was in a collaborative discussion with the agency where we settled on that 12-week endpoint.

Has that happened since the original alignment this year or since you redosed? Or was that originally the alignment?

That's the original discussion. We haven't had reason to discuss the endpoints of the trial once it was agreed and aligned upon.

Ladies and gentlemen, this concludes the question-and-answer session of today's conference call. I'll hand the call back over to Nivi.

Great. Thank you, everyone, for joining today's call. Have a great rest of your day.

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