Tarsus Doses First Participant in Calliope, A Phase 2 Clinical Trial of TP-05 (lotilaner), a Novel Investigational Oral Tablet for the Potential Prevention of Lyme Disease
Rhea-AI Summary
Tarsus (NASDAQ: TARS) dosed the first participant in Calliope, a randomized, double-blind Phase 2 trial of TP-05 (lotilaner) to evaluate safety, tolerability and pharmacokinetics for potential prevention of Lyme disease by killing infected ticks before transmission.
Calliope will enroll ~700 healthy adults across U.S. endemic regions, aims to complete enrollment during the 2026 tick season, and expects topline results in H1 2027. Prior Phase 2a Carpo showed >90% tick kill within 24 hours and statistically significant benefit versus placebo (p<0.001); preclinical mouse studies showed 90% efficacy versus 0% in controls.
AI-generated analysis. Not financial advice.
Positive
- Phase 2 dosing initiated with first participant enrolled
- Planned enrollment of ~700 adults across endemic U.S. regions
- Topline results expected in H1 2027
- Prior Carpo data showed >90% tick kill within 24 hours (p<0.001)
- Preclinical mice studies demonstrated 90% efficacy versus 0% control
Negative
- TP-05 not yet approved; efficacy for human Lyme prevention remains unconfirmed pending Phase 2 results
- Trial outcome timeline depends on enrollment during the 2026 tick season and could change
News Market Reaction – TARS
On the day this news was published, TARS gained 4.83%, reflecting a moderate positive market reaction.
Data tracked by StockTitan Argus on the day of publication.
Key Figures
Market Reality Check
Peers on Argus
TARS is up about 1.01% with mixed peer moves: AGIO up 14.83%, IRON and TVTX modestly positive, while ARQT and OCUL are down. Only AGIO appears in the momentum scanner, suggesting today’s action in TARS is more stock-specific.
Historical Context
| Date | Event | Sentiment | Move | Catalyst |
|---|---|---|---|---|
| Mar 23 | China TP-03 approval | Positive | -0.6% | China approval of TP-03 triggering $15M milestone payment. |
| Feb 26 | Investor conferences | Neutral | -0.5% | Announcement of participation in two major healthcare investor conferences. |
| Feb 23 | Earnings and guidance | Positive | +7.8% | Strong 2025 XDEMVY sales and cash balance with pipeline progress update. |
| Feb 18 | Board appointment | Positive | +0.8% | Appointment of former Allergan CEO David Pyott to board of directors. |
| Feb 17 | Earnings date set | Neutral | +0.8% | Scheduling of Q4 and full-year 2025 earnings release and webcast. |
Recent fundamentally positive news (earnings beat, China approval) has sometimes led to gains but also showed at least one divergence with a mild post-news pullback.
Over recent months, Tarsus has combined commercial growth with pipeline execution. On Feb 23, 2026, it reported 2025 XDEMVY net product sales of $451.4 million and year-end cash of $417.3 million, with shares rising 7.79%. A China approval for TP-03 on Mar 23, 2026 triggered a $15 million milestone but the stock dipped slightly. Board strengthening and investor conferences rounded out the story. Today’s TP-05 Phase 2 dosing extends that pipeline narrative into Lyme disease prophylaxis.
Market Pulse Summary
This announcement marks a key pipeline milestone as Tarsus doses the first participant in the Phase 2 Calliope trial of TP-05 for Lyme disease prevention in about 700 adults. Earlier Carpo data showed tick kill rates above 90% with strong statistical significance (p<0.001). In parallel, the company reported 2025 XDEMVY sales of $451.4 million, underscoring a commercial base supporting development. Investors may watch enrollment progress in the 2026 tick season and topline data expected in the first half of 2027.
Key Terms
phase 2 clinical trial medical
randomized, double-blind, placebo-controlled medical
pharmacokinetics medical
prophylactic medical
proof-of-concept medical
borrelia burgdorferi medical
placebo medical
preclinical medical
AI-generated analysis. Not financial advice.
| – A pioneering investigational oral prophylactic approach designed to kill Lyme-infected ticks before disease transmission – |
IRVINE, Calif., March 31, 2026 (GLOBE NEWSWIRE) -- Tarsus Pharmaceuticals, Inc. (NASDAQ: TARS) today announced that the first participant has been dosed in the Phase 2 clinical trial (Calliope) evaluating TP-05 (lotilaner), a novel investigational oral therapy designed to potentially prevent Lyme disease by killing Lyme-infected ticks before disease transmission occurs.
Calliope is a randomized, double-blind, placebo-controlled Phase 2 trial evaluating the safety, tolerability and pharmacokinetics of orally administered TP-05 in approximately 700 healthy adults at risk for Lyme disease across endemic regions of the United States. Tarsus plans to complete enrollment during the 2026 tick season, with topline results expected in the first half of 2027.
“For decades, Lyme disease management has focused on treating infection after it occurs,” said Bobby Azamian, M.D., Ph.D., Chief Executive Officer and Chairman of Tarsus. “We believe there is an opportunity to fundamentally shift that paradigm toward prevention by targeting the ticks that transmit the disease. The Calliope trial represents an important step in developing what could potentially be the first FDA-approved on-demand oral prophylactic option designed to help prevent Lyme disease.”
“With climate change and the expanding geographic range of ticks infected with human pathogens contributing to a growing burden of tick-borne illnesses, Lyme disease is becoming an increasingly urgent public health challenge,” said Linden Hu, M.D., the Paul and Elaine Chervinsky Professor of Immunology at Tufts University School of Medicine. “Tick bites and early symptoms are often missed, leading to missed diagnoses or delayed treatment, increasing the risk of serious long-term complications. New prophylactic approaches with the potential to help reduce the risk of infection could play an important role in addressing this growing threat.”
There are currently no U.S. Food and Drug Administration (FDA)-approved pharmacological prophylactic options for Lyme disease, the most common vector-borne disease in the United States. Lyme disease is caused by Borrelia burgdorferi infection and transmitted through the bite of infected ticks. According to recent market research, more than 35 million Americans are considered to be at moderate to high risk of contracting Lyme disease, and an estimated 300,000 – 400,000 people are diagnosed annually.
The Calliope trial design was informed by the Phase 2a Carpo randomized, double-blind, placebo-controlled, proof-of-concept “tick kill” study, in which a single dose of TP-05 demonstrated statistically significant tick mortality versus placebo at both Day 1 and Day 30. Tick kill rates exceeded
About TP-05
TP-05 is an investigational oral systemic formulation of lotilaner. It is believed to be the only non-vaccine, drug-based prophylactic in development designed to kill ticks to potentially prevent Lyme disease transmission.
About Lyme Disease
Lyme disease is the most common vector-borne disease in the United States, transmitted to humans by Borrelia burgdorferi infection following the bite of a tick vector. According to recent market research, more than 35 million Americans are considered to be at high or moderate risk of contracting Lyme disease, and approximately 300,000 – 400,000 people in the U.S. are diagnosed and treated each year. Early signs of Lyme disease are often overlooked or misdiagnosed. Left untreated, Lyme disease can potentially cause severe, often debilitating symptoms with permanent and irreversible damage. The disease can result in inflammation, nerve, joint and muscle pain and swelling, numbness, shortness of breath and – in severe cases – neurological complications such as facial palsy, vision issues and meningitis, including severe headaches and neck stiffness, as well as cardiac complications. Data from the Centers for Disease Control and Prevention (CDC) show that the risk of Lyme disease is spreading to new geographical areas, resulting in a significant need for prophylactic solutions. Currently, there are no FDA-approved pharmacological prophylactic options for Lyme disease.
About Tarsus Pharmaceuticals, Inc.
Tarsus Pharmaceuticals, Inc. applies proven science and new technology to revolutionize treatment for patients, starting with eye care. Tarsus is advancing its pipeline to address several diseases with high unmet need across a range of therapeutic categories, including eye care, dermatology, and infectious disease prevention. XDEMVY® (lotilaner ophthalmic solution)
Forward-Looking Statements
Statements in this press release about future expectations, plans and prospects, as well as any other statements regarding matters that are not historical facts, may constitute “forward-looking statements.” These statements include statements regarding our ability to execute clinical studies including the Phase 2 Calliope trial for the potential prevention of Lyme disease, the time frame for results of our clinical studies, and the quotations of Tarsus’ management and advisors. The words, without limitation, “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “potential,” “predict,” “project,” “should,” “target,” “will,” or “would,” or the negative of these terms or other similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these or similar identifying words. Further, there are other risks and uncertainties that could cause actual results to differ from those set forth in the forward-looking statements and they are detailed from time to time in the reports Tarsus files with the Securities and Exchange Commission, including Tarsus’ Form 10-K for the year ended December 31, 2025 filed on February 23, 2026, copies of which are posted on its website and are available from Tarsus without charge. However, new risk factors and uncertainties may emerge from time to time, and it is not possible to predict all risk factors and uncertainties. Accordingly, readers are cautioned not to place undue reliance on these forward-looking statements. Any forward-looking statements contained in this press release are based on the current expectations of Tarsus’ management team and speak only as of the date hereof, and Tarsus specifically disclaims any obligation to update any forward-looking statement, whether as a result of new information, future events or otherwise, except as required by law.
Media Contact:
Adrienne Kemp
Sr. Director, Corporate Communications
(949) 922-0801
akemp@tarsusrx.com
Investor Contact:
David Nakasone
Head of Investor Relations
(949) 620-3223
DNakasone@tarsusrx.com
