Kiniksa Pharmaceuticals International - Earnings Call - Q3 2025

Executive Summary

• Q3 delivered strong topline growth with ARCALYST net product revenue of $180.9M (+61% YoY, +15% QoQ), prompting a second guidance raise this year to $670–$675M for FY25; however, diluted EPS of $0.23 fell below consensus while revenue beat materially.
• Versus S&P Global consensus, revenue beat by ~$13.5M (+8.1%), while EPS missed by ~$0.14 (−37.3%); management attributed higher collaboration expense to stronger collaboration profit on higher sales, pressuring EPS despite positive operating leverage.
• Commercial KPIs improved: prescribers surpassed 3,825 (+350+ new in Q3), average total therapy duration increased to ~32 months, and Q3 was the highest new prescriber quarter since launch—underscoring expanding breadth and durability of adoption.
• Pipeline momentum: KPL‑387 received FDA Orphan Drug Designation (pericarditis) and remains on track for Phase 2 dose‑focusing data in 2H26, supporting a broader IL‑1α/β inhibition franchise narrative and potential future penetration gains.

What Went Well and What Went Wrong

• What Went Well

  • Record commercial execution: ARCALYST revenue rose to $180.9M (+$24M QoQ; +$68.6M YoY), driven by higher active patients, prescriber breadth (>3,825 total; >350 new in Q3), and longer therapy duration (~32 months).
  • Guidance raised again: FY25 ARCALYST net sales increased to $670–$675M (from $625–$640M), reflecting sustained trajectory even as management factors normal year‑end dynamics.
  • Cash strengthening alongside growth: Cash, equivalents, and ST investments rose by ~$44M QoQ to $352.1M with no debt, and management reiterated annual cash‑flow positivity under the current plan.
  • Quote: “We’ve raised our full‑year net sales guidance to between $670 million to $675 million… we expect to continue to grow ARCALYST revenue.” – Sanj K. Patel, CEO.

• What Went Wrong

  • EPS below Street: Diluted EPS ($0.23) missed consensus despite revenue beat; collaboration expense rose with collaboration profit, limiting EPS leverage.
  • Operating expenses accelerated: Total OpEx increased to $156.8M (vs. $136.6M in Q2 and $121.9M in Q3’24), including higher collaboration expenses tied to stronger sales.
  • Modeling headwind items: Growth‑to‑net trended down YTD to 8.9% (from 9.5% YTD in Q2), and the tax rate and collaboration expense ran higher than some Street models (management pointed to sales strength and jurisdictional mix).

Transcript

Operator (participant)

Thank you for standing by and welcome to the Kiniksa Pharmaceuticals Third Quarter 2025 Earnings Conference Call. At this time, all participants are in listen-only mode. After the speaker's presentation, there will be a question and answer session. To ask a question during this session, you'll need to press star one one on your telephone. If your question has been answered and you'd like to remove yourself from the queue, simply press star one one again. As a reminder, today's program is being recorded. Now I'd like to introduce your host for today's program, Jonathan Kirshenbaum, Investor Relations Officer. Please go ahead, sir.

Jonathan Kirshenbaum (Associate Director of Investor Relations)

Thank you, Operator. Good morning, everyone, and thank you for joining Kiniksa's call to discuss our third quarter 2025 financial results and recent portfolio execution. A press release highlighting these results can be found on our website under the Investors section. As for the agenda for today's call, our Chief Executive Officer, Sanj K. Patel, will start with an introduction and overview of our business. From there, Ross Moat, our Chief Corporate and Commercial Officer, will discuss our IL-1 Innovation franchise and provide an update on our first commercial execution. Kiniksa's Chief Financial Officer, Mark Ragosa, will review our third quarter 2025 financial results. Finally, Sanj will share closing remarks and kick off the Q&A session, for which Dr. John Paolini, our Chief Medical Officer, and Eben Tessari, our Chief Operating Officer, will also be on the line.

Before getting started, please note that we will be making forward-looking statements today that are subject to risks and uncertainties that may cause actual results to differ materially from these statements. A review of such statements and risk factors can be found on this slide, as well as under the caption "Risk Factors" contained in our SEC filings. These statements speak only as of the date of this presentation, and we undertake no obligation to update such statements except as required by law. With that, I'll turn it over to Sanj.

Sanj Patel (Chairman and CEO)

Thanks, Jonathan, and good morning, everyone. Year-to-date in 2025, we've continued to execute and meaningfully advance our commercial business and clinical development portfolio. The use of IL-1α and IL-1β inhibition with ARCALYST has increasingly become the preferred treatment for recurrent pericarditis, driving significant ARCALYST revenue growth and positioning our franchise for long-term success, both with ARCALYST and KPL-387. We continue to be excited about the potential of our IL-1 inhibition franchise and fully intend to remain the market leader in recurrent pericarditis. Given the fact that, as last reported, we were only 15% penetrated into the multiple recurrence patient population, we expect to continue to grow ARCALYST revenue. To this point, as announced this morning, we've raised our full-year net sales guidance to between $670 million to $675 million from our previous guidance of $625 million and $640 million.

We also believe KPL-387 could be an important advancement in the treatment options available for patients, potentially increasing penetration and growing the recurrent pericarditis market. We remain on track to report data from the phase 2 dose-focusing portion of the phase 2/3 trial in the second half of next year. Additionally, we are pleased to report that early this month, the FDA granted KPL-387 orphan drug designation for the treatment of pericarditis, which includes recurrent pericarditis. Importantly, we have maintained a robust financial position while continuing to create value without relying on the capital markets. Turning to the growing adoption of IL-1α and IL-1β inhibition with ARCALYST, we've introduced and advanced a fundamental shift in the treatment paradigm for this disease. Ross will share more details about this in a moment.

In the third quarter, ARCALYST revenue grew to $180.9 million, which represents a growth of approximately $24 million over the previous quarter and approximately $69 million compared to the third quarter of 2024. While we're pleased with this growth, we continue to believe in the significant opportunity for additional growth ahead. As of the end of the second quarter, we were only 15% penetrated into the multiple recurrence opportunity, and we continue to see ARCALYST utilized earlier in the course of the disease. As previously stated, approximately 20% of ARCALYST prescriptions have been written for patients following their first recurrence. For patients who failed NSAIDs or colchicine, physicians are more readily turning to targeted dual IL-1α and IL-1β inhibition with ARCALYST, rather than risk an unnecessary flare by treating patients again with a previously unsuccessful treatment.

Overall, the progress we've made reflects the medical community's growing adoption of IL-1 pathway inhibition and speaks to the future value creation of our IL-1 inhibition franchise. With that, I'll turn it over to Ross.

Ross Moat (Chief Corporate and Commercial Officer)

Thank you, Sanj. The growing understanding of recurrent pericarditis, being driven by the cytokines interleukin-1α and interleukin-1β, has been a key driver behind the growth we've seen in the adoption of ARCALYST. As an increasing number of healthcare professionals update their approach in how to treat recurrent pericarditis with targeted IL-1 immunomodulation, we've seen a substantial increase in the number of active commercial patients on ARCALYST. Specifically, this is a result of our team driving increases in two key areas. Firstly, in Q3, new patient enrollments grew by their highest level in a quarter since launch.

This is represented in the growth of prescribers of more than 350 in the quarter, leading to a total prescriber count launched to date of more than 3,825, including around 28% or more than 1,000 prescribers who have written ARCALYST for two or more patients. Secondly, once on treatment, patients are staying on ARCALYST for longer, which speaks to both the duration of the disease and patient satisfaction on ARCALYST. At the end of Q3, the total average duration of therapy increased to approximately 32 months. These two levers increased the number of active commercial patients and contributed to our ability to raise our revenue guidance for the full year 2025.

Our commercial organization has been highly focused on evolving the treatment landscape for patients suffering from this chronic, highly debilitating disease by increasing education and driving the utilization of interleukin-1α and interleukin-1β inhibition towards becoming the new standard of care for recurrent pericarditis. We have built a highly effective commercial infrastructure and built upon many years of established relationships with the recurrent pericarditis community to improve the care for patients. In the four and a half years since the launch of ARCALYST, we've continued to hone our messaging, and we've improved our effectiveness through utilization of AI and digital marketing to inform which physicians to visit and, importantly, when they're most likely to see a recurrent pericarditis patient.

Thanks to the compelling clinical and real-world data generated in Rhapsody and Resonance, our payer approval rate remains very high, and we continue to be focused on delivering excellent support to patients through Kiniksa One Connect, our patient services program. This combination of robust data, access, and support enables healthcare professionals to feel confident that their patients will get onto therapy, be well-supported, and receive the type of efficacy we've seen in the published literature. As a result of the continued growth in patients on ARCALYST, today we raised and tightened our full-year 2025 ARCALYST net sales guidance from between $625 million to $640 million to now between $670 million and $675 million, which is a $40 million increase in guidance between the midpoints.

Our increased guidance reflects the robust trajectory of ARCALYST revenue in 2025, while also accounting for typical year-end industry dynamics, which is consistent with our historical fourth quarter performance. As you've heard, we're pleased with our solid execution and progress and are incredibly excited about the opportunities we have ahead. As we continue to focus on maximizing the growth of ARCALYST, we are also excited about the opportunity to advance the care of recurrent pericarditis patients in the future with KPL-387, our development program. This is our fully owned monoclonal antibody antagonist targeting the IL-1 receptor to inhibit both IL-1α and IL-1β. The totality of data shows that inhibiting the activity of both of these key cytokines is a core component of delivering a highly efficacious treatment for recurrent pericarditis.

With this program, we're advancing a validated mechanism with the potential to address key patient needs and expand penetration into the addressable market by enabling a convenient monthly subcutaneous dose in an autoinjector. Surveyed patients and healthcare professionals have indicated a preference for a highly efficacious IL-1α and IL-1β inhibitor with this target profile. Specifically, approximately 75% of all surveyed recurrent pericarditis patients report that they would prefer the KPL-387 target profile over those of available commercial and current investigational therapies. On the physician side, more than 90% of healthcare professionals stated a high likelihood of prescribing KPL-387 for new patients, as well as being receptive to switching current patients upon a patient's request. It's also worth noting that healthcare professionals broadly agree that the introduction of KPL-387 would expand the IL-1α and IL-1β inhibition market overall.

As we've previously announced, the dose-focusing portion of the phase 2/3 development program of KPL-387 is currently underway, and we expect those data in the second half of 2026. With that, I'll turn the call over to Mark Ragosa to review our third quarter financials. Mark.

Mark Ragosa (CFO)

Thanks, Ross. This morning, I will cover our third quarter 2025 financial performance. Our detailed results can be found in the press release we issued earlier today. There are several items on this slide that I'd like to call your attention to, starting with our income statement on the left-hand side. First, ARCALYST revenue grew 61% year-over-year in the third quarter to $180.9 million, with adoption of IL-1α and IL-1β inhibition for recurrent pericarditis continuing to drive significant gains in active commercial patients and duration of therapy. Second, operating expenses grew 29% year-over-year in the third quarter to $156.8 million, primarily due to collaboration expenses, which were driven by continued strong ARCALYST collaboration profit growth.

Third, due to strong revenue growth against more moderate operating expense growth, net income was $18.4 million in the third quarter of 2025, compared to a net loss of $12.7 million a year ago. The right-hand side of this slide provides the calculation of ARCALYST collaboration profit, which drives collaboration expenses. ARCALYST collaboration profit grew a significant 118% year-over-year to $126.6 million in the third quarter, as profit split eligible COGS, as well as commercial and marketing costs, held steady against higher sales. Lastly, at the bottom of this slide, we continue to expect our current operating plan to remain cash flow positive on an annual basis, and in the third quarter, our cash balance increased by approximately $44 million to $352.1 million.

As you've heard from Sanj and Ross, we further advanced our commercial business and clinical portfolio, as well as maintained a strong balance sheet in the third quarter. As a result, Kiniksa added to its significant momentum and remains well-positioned to continue to help patients, as well as to create additional value in both the near and long term. With that, I'll turn the call back to Sanj for closing remarks.

Sanj Patel (Chairman and CEO)

Thanks, Mark. As you've heard, Kiniksa continues to execute both commercially and clinically, and we are well-positioned to build significant future value as we grow our IL-1α and IL-1β inhibition franchise. As ever, we are committed to bringing additional treatment options to patients that are suffering from debilitating diseases with unmet need. I'll now turn the call back to the operator for questions. Thank you.

Operator (participant)

Certainly. Our first question comes from the line of Geoff Meacham from Citi. Your question, please.

Mary Kate (Head of Art Advisory)

Morning. This is Mary Kate on for Geoff. Thank you so much for taking our question. You're seeing duration increase here for ARCALYST, which is encouraging. Could you comment on maybe the patient and physician feedback you're hearing from these longer users? Thank you.

Sanj Patel (Chairman and CEO)

John, do you want to take that?

John Paolini (CMO)

Sure. In general, what we're seeing, certainly in terms of the academic literature, is an appreciation of the duration of disease, and therefore the necessity of treating to that duration of the disease in order to minimize the amount of recurrences that patients experience. What we know from the literature is that the median duration of disease is three years, with a third of patients still suffering disease at five years and a quarter at eight years. The other data that we have, in fact, which we recently shared at the European Society of Cardiology meetings, is that continued treatment without interruption resulted in a 99.5% reduction in event rates post-treatment or on treatment compared to pre-treatment. That creates a very powerful message, if you will, for clinicians that treating to the duration of the disease is the best way to manage the disease.

Ross Moat (Chief Corporate and Commercial Officer)

Thanks, John. Maybe just to add on top of that as well, in terms of the healthcare professional patient feedback that we're getting, generally, we receive very positive feedback for those patients that have been on therapy for quite some time and a growing amount of time up to now, 32 months on an average total duration of therapy. What we see on the healthcare professional side is generally due to the high access rates that we get, that the healthcare professionals see their patients get onto therapy reasonably quickly and easily thanks to the higher approval rate. That kind of provides confidence that their patients are going to get onto therapy and helps them to then look for future patients, knowing that their patients will get onto therapy.

For the patients themselves, the fact that they've been on therapy for longer, I think, is also part of the evidence of doing well on therapy. We continue to hear very high satisfaction from patients on therapy, and I think that backs up what we've seen both in the clinical world and the real-world evidence of how highly efficacious and well-tolerated this drug is. As a reminder, it's been designed to be used over the course of the treatment, the duration of the disease, and to match that duration of the disease with the treatment duration. This has really been designed as a long-term therapy to address what is a chronic multi-year and highly debilitating disease for most patients. The feedback has really been very good from both healthcare professionals and patients overall.

Operator (participant)

Thank you. Our next question comes from the line of Anupam Rama from JPMorgan. Your question, please.

Anupam Rama (Managing Director and Senior Equity Analyst)

Hey, guys. Thanks so much for taking the question and congrats on the quarter. Can you talk a little bit about how you guys have incorporated the updated ACC guidelines into your marketing efforts and what the early innings, what you've learned from the guideline update? I think that was just a couple of months ago, right, in August of this year? Thanks so much.

John Paolini (CMO)

Hi, Anupam. Thanks for the question. I'll start off with a brief summary of the concise clinical guidance and then hand it over to Ross regarding your question about incorporation of the guidance into the fieldwork. Specifically to the concise clinical guidance, this is really, you know, this came out in August and represents an affirmation of what we've seen from the literature and actually driven by the data that we've helped to generate, which is positioning IL-1 pathway inhibition as second line after NSAIDs and colchicine, which is a real advance in the treatment paradigm to be truly steroid-sparing. That was driven by the initial data from the Rhapsody study, where half the patients were treated second line after NSAIDs and colchicine.

That was then picked up from our Resonance registry showing year-on-year after the approval of ARCALYST, a reduction in the use of corticosteroids and a rise in IL-1 pathway inhibition led by ARCALYST in the treatment of these patients. That was then picked up by JACC Advances and JACC Imaging in the thought leader literature. Ultimately, it culminated, if you will, in the concise clinical guidance, which is a real affirmation from a practice entity to provide guidance to clinicians. That creates that strong foundation that Ross and his team have been building on. Ross, over to you.

Ross Moat (Chief Corporate and Commercial Officer)

Thank you, John. I think it was really much-needed guidance that we were pleased to see, given that this is really the first U.S.-focused guidance publication that's really out there. We're utilizing it certainly within a promotional perspective and incorporating it within promotional materials. As John said, it's really an affirmation of the type of messaging that we've really been providing since launch. It's wonderful to have further publications from experts in the field affirming the type of approach and new approach to managing this disease compared to historic available drugs, and in particular around the utilization of corticosteroids, which we've always promoted ARCALYST as a really steroid-sparing agent and a drug which should be utilized ahead of corticosteroids.

Having this type of publication out there, which we have incorporated within our materials now as well from a promotional perspective, is a huge help, knowing that the use of corticosteroids is probably not the most advanced way of treating this condition now that there is a targeted immunomodulation approach, specifically looking at the key driver of this disease, which is interleukin-1 alpha and beta, and being able to inhibit that. We really see as the modern way of treating this disease, and we hope will become the new standard of care.

Anupam Rama (Managing Director and Senior Equity Analyst)

Thanks so much for taking our question.

Operator (participant)

Thank you. Our next question comes from the line of Roger Song from Jefferies. Your question, please.

Roger Song (Senior Equity Research Analyst)

Great. Congrats for the quarter, and thank you for taking our question. My question is related to the first occurrence. Since your revenue is driving very well, penetration continues to be very good. How should we think about the first occurrence if that's the population you will start to think more about? What could drive further penetration into that population? Thank you.

Ross Moat (Chief Corporate and Commercial Officer)

Yeah. Thanks, Roger. This is Ross again. Yes, as you noted, we have seen an increase over time in how physicians are utilizing ARCALYST within the first recurrence of recurrent pericarditis. As a reminder, that really is the breadth of the label. The label is completely agnostic to the number of flares a patient must have gone through and suffered from before they become eligible for this targeted immunomodulation therapy. We have promoted it to recurrent pericarditis overall. Certainly, early on in the launch, we did see the physicians were utilizing it more within the two-plus recurrence group, which is the 14,000 patient population in any given year. We've seen a lot of utilization there.

I think as physicians become more and more comfortable and familiar with how to prescribe the drug, and then going back to the first question, that the physicians and patients have a good experience when they're on the drug, and in fact, they get access to therapy and see the type of results that we've seen in the clinical world, that provides greater confidence of using it earlier on in the disease. I think what we're seeing is physicians taking a mindset of why should we let patients continue to suffer from additional flares before they become eligible for this targeted treatment. We have seen now around 80% of our patients that are prescribed ARCALYST within the two-plus recurrence group, and around 20% of all of those that are prescribed ARCALYST within the first recurrence group. Obviously, that has grown in percentage terms over time.

As we said in the prepared remarks, we are incredibly excited about the future opportunity, knowing that we announced midway through this year that we were around 15% penetrated into the two-plus recurrence group without even taking into account those patients in the first recurrence. The opportunity ahead to serve many, many more patients, while we're happy with our current commercialization, the future is certainly there for us to address and help many more patients in the future.

Roger Song (Senior Equity Research Analyst)

Excellent. Thank you.

Operator (participant)

Thank you. Our next question comes from the line of Eva Fortea-Verdejo from Wells Fargo. Your question, please.

Eva Fortea-Verdejo (Biotech Equity Research Analyst)

Good morning. Thanks for taking our questions and congrats on the quarter. Two from us. First, on ARCALYST, can you discuss the growth dynamics for the quarter? Second, on KPL-387, what will be the drivers of your decision on the phase 3 dose, given that, if I recall correctly, the phase 2 is powered to demonstrate a statistical difference? Thanks.

Mark Ragosa (CFO)

Thanks, Eva. I guess first on the growth to net, for the quarter year to date, it was 8.9% down from 9.5% year to date in the second quarter. It was lower and in line with our historical pattern where we see it highest in the first quarter due to industry dynamics such as benefit plan resets and copay support, and then lower in the second and the third quarter, and then moving slightly higher in the fourth quarter as industry dynamics begin to play a factor again.

John Paolini (CMO)

Eva, thanks for the question about KPL-387 dosing. Importantly, the phase 2 portion of the study is a dose-focusing type study rather than a formal dose-ranging type study. That is because our modeling has shown that the 300 mg subcutaneous dose, which in healthy volunteers lasts for almost two months, should provide sufficient coverage for monthly dosing. Therefore, the phase 2 study is designed really anchored on that 300 mg subcutaneous every month dose, and then looking to see that 300 mg given every other week does not provide additional efficacy, and that lower doses exhibit weakness, which would then all affirm the use of the 300 mg subcutaneous dose level. That is how we will look at that information and move forward into phase 3. Thank you for the question.

Eva Fortea-Verdejo (Biotech Equity Research Analyst)

Got it. Thanks.

Operator (participant)

Thank you. Our next question comes from the line of Nick Larissa from TD Cowen. Your question, please.

Nick Larissa (Vice President and Biotech Equity Research Analyst)

Thanks very much for taking the question and congrats on the great quarter. Can you discuss what drove the strong increase in the number of prescribers this quarter compared to last quarter, and what the plan is to continue this uptake? Also, what proportion of recurrent pericarditis patients do the 3,800 current ARCALYST prescribers actually see? Thank you.

Ross Moat (Chief Corporate and Commercial Officer)

Sorry, Nick. Can you just repeat the last part of the last question? I just paid you off.

Nick Larissa (Vice President and Biotech Equity Research Analyst)

Yeah. What proportion of recurrent pericarditis patients do the 3,800 prescribers see?

Ross Moat (Chief Corporate and Commercial Officer)

Okay. Thanks very much. Let me answer the question, and please come back if it doesn't answer it fully. Yeah. We've seen that there's been a significant increase in the number of prescribers. This is actually in Q3, the highest increase that we've seen in any quarter launched to date. That's more than 350 new prescribers coming in who have never prescribed ARCALYST before, prescribing it for recurrent pericarditis. That takes the total to more than 3,825. About 28% of that total group have written for two or more patients. I think the things that lead into that is just more confidence, more awareness of ARCALYST as the treatment choice. I'm sure the ACC guidance has also been somewhat of a help towards that, just providing more validation, if you like, of the way of how to treat this disease.

Our team have been very targeted in their approach, both our sales team in the field calling upon healthcare professionals. We've done a lot of work to really try to understand where the patients are presenting into. As a reminder, this is a disease space where the patient population is pretty widely dispersed. There's the opportunity to go into many physicians, or there's the opportunity for recurrent pericarditis patients to go into many physicians. I think we're getting better at both honing our messaging as well as understanding the patient throughput, and not only which physicians these patients are going into, but also using more innovative technology to play through when we believe those patients are going to be visiting healthcare professionals. We're using a lot of kind of AI and digital innovation approaches to guide our field team.

On the other side of that, we're also very focused on digital marketing and making sure that our messaging around ARCALYST and recurrent pericarditis goes far and wide across the population outside of our in-person resources. There's a lot of tactics that we have to try to drive that. We've seen some substantial growths, and that's certainly a big part of the Q3 results that we've seen. As we know, there's still a significant opportunity ahead for us.

We're very focused on continuing the breadth, growing the breadth of prescribing, as well as being very focused on once someone is prescribed once, helping them to support and find the second patient and the third patient and onwards, because we know there's a significant population out there who unfortunately still get a very high level of either underdiagnosis or misdiagnoses, as evidenced in a Harris poll, which showed that there was an average of 2.7 misdiagnoses before patients end up with a correct diagnosis of recurrent pericarditis. We have an awful lot of work still to do, but the opportunity to grow the breadth and depth is pretty significant.

Nick Larissa (Vice President and Biotech Equity Research Analyst)

Thank you very much. Appreciate it.

Operator (participant)

Thank you. Our next question comes from the line of Paul Choi from Goldman Sachs. Your question, please.

Paul Choi (Biotechnology Analyst)

Hi. Good morning, and congratulations on the quarter. I have a few questions. My first is for Ross, and thanks for all the details on the slides. For the 45% of patients who restart versus the other sort of half or 55% who don't, can you maybe walk us through why they're not restarting and just sort of what the commercial efforts are to chase these patients? My second question is for Mark. Both the collaboration expense and tax rate came in higher than I think the street were modeling. Can you maybe just remind us if there are any one-offs on both those line items for this quarter and if that should be the sort of the run rate going forward in terms of our modeling? My third, maybe for John, is a competitor will have phase 2 proof of concept data in RP in the not-too-distant future.

Can you maybe just remind us of how you're thinking about this? Are you assuming clinical success, and how you think the data might compare to Rhapsody? Thanks for all the questions.

Ross Moat (Chief Corporate and Commercial Officer)

Thanks very much for those questions, Paul. I'll make a start on the first one, then hand over to Mark and then to John for the final question. Thank you very much for that. Your initial question on ARCALYST is around the 45% restart rate and those patients that are not restarting and why is that. Actually, we have a slide that provides a bit of detail on the duration of therapy on our corporate deck as well. This ultimately shows that the average time of the initial treatment is now around 17.5 months, up from 17 months at our last earnings call. The median is around 12 months.

The fact is that depending upon when a patient starts on therapy and how long they've suffered with the disease prior to the initiation of ARCALYST is one of the several factors that goes into a healthcare professional's judgment call on how long a patient needs to be on therapy for. When patients stop, on average initially at 17.5 months, there's around 45% of those patients that come back onto therapy. As a reminder, when patients do come back onto therapy, it's generally very quick in terms of around eight weeks or within an eight-week time period for the vast majority of the patients that restart, which makes perfect sense when you think about the washout time and the tenacity of the underlying disease. For those patients that don't restart therapy, we don't collect very much data on that.

It's difficult to know precisely why patients don't come back onto therapy other than to make assumptions on that, which could be around the fact that they are just through the disease and they stop and don't suffer from symptomology again and don't come back onto therapy. The good news is when patients do come back onto therapy, whether it's within the eight-week time period or indeed much longer, which is for a minority of patients, when they do come back onto therapy, it's generally a very easy and quick process for them to do so. Generally, there's a payer approval already in place. It's quite easy to get the next shipments of ARCALYST ready. We know that when patients go back onto therapy after suffering symptomology again, they come back under control very quickly with ARCALYST. That's what we've seen around the initial and the restarts.

That's the totality of adding up the treatment periods, which for some patients is several stops and restarts over time. That takes us to the average total duration of therapy now of 32 months, up from 30 months at last reported. Mark?

Mark Ragosa (CFO)

Great. Yeah. Thanks, Paul, for the question. As it relates to sort of your P&L questions, we don't provide specific guidance, but clearly, collaboration expense was up quarter-over-quarter and year-over-year, and largely due to ARCALYST sales growth. As we kind of detailed in the prepared comments, collaboration expenses are largely driven by continued ARCALYST sales growth, which was very strong in the quarter. I would say regarding tax, the drivers remain the same as they have in past quarters as well. Tax on income earned in the U.K., Switzerland, and the U.S., net of Citi R&D and stock-based comp credits.

John Paolini (CMO)

Paul, this is John. Thanks for your question about the competitive landscape. Yes, the field is awaiting data from an inflammasome inhibitor, phase 2 data. In that sense, not so much Rhapsody, but rather those data are structured in some way similar to the phase 2 data that we had reported for REG back in 2019 at the beginning of the program, which is relatively short-term therapy and mostly single active arm. In that sense, you would expect with near-term, short-term therapy, especially if you have an inflammasome inhibitor, and an inflammasome is, of course, the driver of IL-1β, which then causes IL-6 production, which goes to the liver, which is where the C-reactive protein comes from. You might expect to see a good inflammasome inhibitor, just like colchicine, should bring C-reactive protein down. The point is that the inflammasome is relatively downstream in the pathophysiology of recurrent pericarditis.

As you know, when the pericardiocyte is injured, IL-1α is released as a preformed cytokine as an alarmant, and that sets off a localized inflammatory response, which itself causes pain and damage. It does then trigger the inflammasome, which then causes the recruitment of that broader inflammatory response. That is why we're really focused on blocking both IL-1α and IL-1β in order to control the disease. That is what we showed in Rhapsody in a longer phase 3 program where you have continued treatment, initially over nine months, but ultimately over 18 months, and then ultimately out to three years, where we showed a 99.5% reduction in events once patients were on treatment, and that the only events that occurred were during the setting of brief study drug interruptions.

In that sense, a drug like ARCALYST is designed to be given long term, and it remains to be seen whether other strategies could be successful. That kind of sets the bar, if you will, for what effective therapy looks like.

Paul Choi (Biotechnology Analyst)

Okay. Great. Thanks for taking our questions.

Operator (participant)

Thank you. Our next question comes from the line of David Nierengarten from Wedbush Securities. Your question, please.

David Nierengarten (Senior Biotechnology Equity Analyst)

Hey, thanks for taking the question. I had one on the transition arm of the KPL-387 study, and I was just wondering if you were biasing the study to different prior therapies. Are half the patients going to be previously treated with steroids, or is it just an even split among prior therapies? Thanks.

John Paolini (CMO)

Thanks, David. Appreciate the question. Your question is about the transition to monotherapy dosing and administration study, which is a supplemental study as part of the total filing package. This study is designed to help inform clinicians how to move patients onto KPL-387 from other prior therapies. That includes really the totality of therapies that are available, so NSAIDs and colchicine, corticosteroids, and other IL-1 pathway inhibitors. It is a global study, so it covers those practice patterns across the world. The study is designed to capture that information and to test the efficacy and safety of those dosing paradigms that are used in order to make that transition to KPL-387 monotherapy. It is designed to capture the necessary information for each one of those types of transitions in order to provide critical information, if you will, for the label to advise clinicians.

There is not necessarily, nor does there need to be, any type of pre-specified hypothesis or specific population balance other than giving the necessary information to inform regulatory authorities' positions on how that works.

David Nierengarten (Senior Biotechnology Equity Analyst)

Okay. Thanks.

John Paolini (CMO)

Thanks, David.

Operator (participant)

Thank you. This does conclude the question and answer session of today's program. I'd like to hand the program back to Sanj Patel, Chairman and Chief Executive Officer, for any further remarks.

Sanj Patel (Chairman and CEO)

Thanks, Operator. Thanks, everybody, for joining the call today and for the questions, of course. We look forward to the remainder of the year and providing additional updates in the future. In the meantime, we will crack on. Thank you.

Operator (participant)

Thank you, ladies and gentlemen, for your participation in today's conference. This does conclude the program. You may now disconnect. Good day.