We have made a lot of progress with the FDA in designing the development path for ISS and intend to refine the design of our Phase III program as data emerge from the Phase II program, including the results of dose selection from the planned study. In conclusion, we are pleased with our rapid progress building out BioMarin’s leadership in multiple growth-related conditions, and we look forward to updating you on our progress with these clinical programs in the coming months. Thank you for your attention, and I’ll now turn the call over to Brian for our financial updates.
Brian Mueller: Thank you, Hank. Please refer to today’s press release summarizing our financial results for full details on the first quarter of 2024, including reconciliations of GAAP to non-GAAP financial measures. All first quarter 2024 results will be available in our upcoming Form 10-Q, which we expect to file in the coming days. In the first quarter of 2024, BioMarin generated record total revenue of $649 million, representing 9% year-over-year growth, 13% on a constant currency basis, driven by continued strong demand for VOXZOGO. Our base portfolio of products, including KUVAN, contributed $484 million of net product revenues in the first quarter. Looking more closely at net product revenue in the first quarter, VOXZOGO revenues of $153 million represented 74% year-over-year growth, that level of growth was despite the supply constraint on VOXZOGO discussed last year and expected to continue through the second quarter of this year.
Our plan for supply to satisfy the forecasted commercial demand around the middle of this year remains intact. 21% revenue growth of PALYNZIQ in the first quarter demonstrated continued momentum for the only biologic approved for the treatment of PKU, offset by lower KUVAN revenues as expected. With NAGLAZYME and ALDURAZYME contributions in the first quarter were not surprising given the usual variable global ordering patterns for those brands. Importantly, we continue to observe commercial patient growth in these brands that we expect will drive sustainable revenue growth over time despite the quarterly order timing. GAAP R&D expenses in the first quarter were $205 million, an increase of $33 million year-over-year, primarily due to increased early-stage research activities as well as increased activity in our clinical programs.
GAAP SG&A expense in the first quarter was $226 million, representing a year-over-year increase of $15 million, driven by the continued support of the global VOXZOGO market expansion, as well as corporate expenses in the quarter. This financial performance in Q1 drove an operating margin of 13.6% on a GAAP basis and 23.8% on a non-GAAP basis. Moving to the bottom line. GAAP net income for the first quarter was $89 million, an increase of $38 million year-over-year and representing GAAP diluted earnings per share of $0.46. Non-GAAP income for the first quarter was $140 million, representing non-GAAP diluted earnings per share of $0.71 and growth of 18% over the same period in 2023. The R&D prioritization decisions made in the first quarter will positively impact non-GAAP diluted earnings per share in 2024, due to now lower levels of expected R&D expense in the second half of 2024 versus prior guidance.
We estimate that the discontinuation of the four programs announced today will result in a reduction of between $50 million to $60 million in R&D expense in 2024. And as Alexander and Hank mentioned, we are prioritizing three of our pipeline assets as well as the VOXZOGO indication expansion. And we identified opportunities to accelerate the development of those assets this year. Therefore, there is a planned offsetting increase in 2024 R&D expenses of approximately $15 million to $20 million which, together with the planned reductions, we extract will result in lower projected R&D expense for the full year of between $35 million to $40 million. Those anticipated net R&D spend reductions in 2024 are driving an expected increase to our non-GAAP operating margin guidance to 24% to 25%.
And an increase to our full year non-GAAP diluted earnings per share guidance to between $2.75 to $2.95 per share. Noteworthy is that we are maintaining our prior projections for the full year, except for the changes in R&D, including total revenue guidance, which remains the same as communicated in February. Also, this update does not include the impact of any further potential strategic business decisions and potential future cost efficiencies to be discussed at Investor Day. As we look forward to Q2 2024, we continue to anticipate limited revenue growth in Q2 versus Q1 due to the timing orders — timing of orders for the enzyme products and similarly for VOXZOGO, while we manage through the supply constraint. We expect higher operating expenses in Q2 versus Q1 due to normal quarterly business dynamics, our various 2024 strategic initiatives and the timing of expenses.
With all this in mind, we expect limited total revenue growth in Q2 versus Q1, and we expect non-GAAP operating margin and EPS to be lower in Q2 than in Q1. In the second half of ’24, we anticipate more meaningful revenue growth as we expect VOXZOGO supply constraints to be resolved. From an expense point of view, we expect all of the reduced R&D for the discontinued programs announced today to begin to be realized in the beginning of Q3 through the end of the year. Lastly, while we plan to share our updated capital allocation strategy at Investor Day regarding our $495 million of convertible notes maturing in August of this year, we plan to leverage our strong cash position and expected operating cash flow to repay the notes with available cash.
Furthermore, given the settlement structure of the notes, we are planning for a share neutral outcome should the notes be in the money at maturity with the goal of returning value to shareholders by avoiding the potential dilution associated with the 4 million underlying shares. As we move into our next chapter of BioMarin, we are executing on our growth strategy with impressive performance driven by VOXZOGO in achondroplasia in our pursuit of new indications, a durable and growing enzyme products business and an increased focus on streamlining the business through cost structure transformation and operating model efficiencies. Together, this presents an opportunity to drive meaningful improvements in our financial performance and sustainable shareholder value creation.
Thank you for your continued support, and we will now open up the call to your questions. Operator?
Operator: Thank you. We will now begin the question-and-answer session. [Operator Instructions] We’ll go first to Phil Nadeau at TD Cowen.
Phil Nadeau: Good evening. Thanks for taking our questions and congratulations on good quarter. Just wanted to follow up on your comments on ROCTAVIAN. Can you give us some sense of what you need to see to support continued investment in the ROCTAVIAN program or maybe asked another way, what would you have to see over the next several months in order to decide to out-license ROCTAVIAN or curtailed future investments there? Thank you.
Alexander Hardy: Thanks very much for the question, Phil. As you heard today, our focus from the R&D side is to allocate assets to the highest value and clearly, we have a high level of current ROCTAVIAN investments and continued challenges with commercial uptake. What we’re saying today is that at Investor Day, we will communicate our evaluation criteria, and the timing for that valuation criteria at Investor Day on the September 4. The possible outcomes of that, I’ll just elucidate. One would be that we see the uptake, the ramp starting to happen in a meaningful way, and that would be a state of course approach would be the outcome. The second would be, we see a lower potential for the asset and a path towards a reasonable return on investment by right-sizing the level of investment across the organization from an R&D, medical affairs and commercial standpoint.
And thirdly, the third possible outcome would be, we remove it from our portfolio, and we divest the asset. So we’re not ready yet to share the evaluation criteria or when valuation criteria timing would be, but we will provide more information on this at Investor Day. I just wanted to also highlight that even as we speak right now, we’ve really focused our strategy and execution with ROCTAVIAN. We’re focused on the site level pull-through of the patients in the three major commercial markets where reimbursement established, United States, Germany and Italy. We have focused our life cycle management activities. So the ongoing studies, ones where we feel that there is a high potential, which is the prior inhibitor population, the registration in Japan.
And we will continue to drive towards an evaluation and communicate more at Investor Day. Thank you, Phil.
Operator: We’ll go next to Geoff Meacham at Bank of America.
Geoff Meacham: Good afternoon, guys. Thanks for the question. I know you’ve talked about label expansion for VOXZOGO being of the highest important strategically. I guess the question is, in the near term, what are the next steps in optimizing the current formulation for VOXZOGO? I wasn’t sure what the cadence of data coming up is for that. Thank you.
Henry Fuchs: Yeah. Hi, Geoff. Hank here. So big picture, absolutely, your question started in the right direction, which is all of the activities that are underway to expand our CNP franchise into as many areas where there’s potentially transformative medical benefit for children with statural impairments, not least of which is entering into a Phase III registration-enabling trial in hypochondroplasia and as I delineated, we’re now well underway in terms of idiopathic short stature. And we’re really making great progress with our long-acting formulation. So in the category of additional presentations to delight patients, we have a lot of stuff that’s also going on internally that for proprietary reasons, we won’t detail until we’re ready to get a little further along.
