Michael Benkowitz
Analyst · Morgan Stanley
Thanks, Martine. I will. Good morning, everybody. As Martine noted, today, we report yet another quarter of record revenue at $678 million and 34% growth from the first quarter of 2023. We saw meaningful growth for all of our key products, Tyvaso Orenitram, Remodulin and Unituxin. Before I get into the details on each of the products, I just want to take a moment to thank all of our fellow Unitarians for an amazing quarter.
First, I want to talk about Tyvaso, which when viewing the nebulizer and dry powder inhaler delivery systems together represents our largest product and remains the #1 prescribed prostacyclin treatment in the U.S. Total Tyvaso revenue for the first quarter was $373 million, up 56% over last year, with growth led by continued uptake of Tyvaso DPI, our regular annual price increase and the increased commercial utilization following the implementation of the Part D redesign provisions under the Inflation Reduction Act, or IRA. Again, this quarter, there were no material changes in inventories of Tyvaso DPI at our specialty pharmacy distributors.
During the first quarter, and both distributors remain within their contracted inventory levels. After a relatively consistent monthly referral rate over the course of 2023, referrals are what we call prescriptions, we saw a nice positive trend break in referral levels for both DPI and Nebulizer in the first quarter with about a 10% to 15% total increase in monthly referrals. This is continuing at least so far into the second quarter. Patient starts also increased, but at a lesser rate during the first quarter, but this is not surprising as there is often a many week lag between referrals and starts. But it does appear that starts per month are increasing in line with the first quarter referral level into the second quarter.
During the first quarter, we were pleasantly surprised to see an increase in commercial utilization of Tyvaso due to the implementation of the IRA. We were expecting to see this increase began in the second quarter as patients reach are out-of-pocket maximums. We expect commercial utilization will continue to increase over the balance of the year. Lastly, on Tyvaso, we're well positioned for competition should it come to market this year. The sales force expansion that we began last year is now complete and fully deployed as of January 1. We expect that we'll start to see the impact of this enhanced sales team beginning in the second half of the year.
We are also now engaging regularly with HCPs or health care providers on the key characteristics of our DPI device, namely that Tyvaso DPI requires only 1 breath per cartridge. Our low flow design requires less patient breadth than high-flow devices, which we believe will be beneficial to patients with compromised lungs. The low flow design also allows for a more efficient delivery of treprostinil relative to the nebulizer and other treprostinil DPI devices. And finally, the BREEZE study demonstrated 98% patient satisfaction with Tyvaso DPI. As I said on our last call, these factors, coupled with the experienced physicians have gained through the rapid uptake of Tyvaso DPI since launch, lead us to believe that Tyvaso DPI will compete effectively with similar product offerings in the inhaled market, given our presence in the PAH and PH-ILD community, our commitment to patients and platform of both nebulized and dry powder delivery options.
Moving to Orenitram. We are very excited to report that not only did we achieve record revenue for the quarter, but we eclipsed $100 million in the quarter for the very first time, reaching $106 million during the first quarter, up 20% from the prior year. This was driven by a combination of increased commercial utilization, pricing of what we consider to be an extremely modest inventory buy-in during the quarter, counter to the normal seasonality we experienced with the Orenitram patterns in the first quarter of the year. Because Orenitram is a Medicare Part D is a drug, like Tyvaso DPI, we saw a meaningful increase in commercial utilization for Orenitram due to the implementation of the IRA. Our medical teams continue to have scientific discussions with health care providers on the EXPEDITE induction protocol where PAH patients initiate therapy on Remodulin and then transition to Orenitram based on recent scientific publications as an option for appropriate patients who may not want or need to go on long-term parenteral therapy.
Transitioning to Remodulin. Worldwide Remodulin revenue was $128 million was up 5% from last year with very strong performance across all of our underlying demand metrics. And this is almost 5 years since the first launch of the generic for Remodulin, reflecting our continued commitment to our patients and the product. Remodulin, both intravenous and subcutaneous remains the most prescribed parenteral prostacyclin in the U.S. We expect this momentum to continue, given the high level of referrals and starts in the first quarter. Our Remunity Pump remains the only option for new subcutaneous patient starts. And we have heard through the channel that specialty pharma distributors are beginning to proactively convert -- beginning to proactively convert remaining subcu treprostinil patients to our immunity pump given the discontinuation of support for the CAD MS3 system by its manufacturer.
Regarding the recent approval of the first active inhibitor, based on conversations with physicians, both before and after approval, we expect many practices will take a measured stance toward its wide use and most used initially could be consistent with the product's clinical evidence, largely in combination use with a prostacyclin therapy. Finally, moving to Unituxin. Worldwide revenue of $58 million, a record, was up 19% from the prior year quarter, and U.S. Unituxin revenue was $53 million, was up 21%. U.S. growth was driven by both price and volume.
To wrap up, following this record quarter, we remain confident that we have the product portfolio, marketing muscle, support structures, clinical data and commercial expertise to continue to grow in both PAH and PH-ILD.
With that, I'll turn the call back over to Martine to run the Q&A.