“An effective oral option allows us to treat earlier – and potentially transform patient quality of life”
Refractory herpes simplex virus (HSV) infection remains a persistent and often debilitating complication in immunocompromised patients, particularly following transplantation. At the 52nd Annual Meeting of the European Society for Blood and Marrow Transplantation (EBMT) in Madrid, Dr Genovefa Papanicolaou (Memorial Sloan Kettering Cancer Center) presented results from the phase III PRIOH-1 trial, highlighting the efficacy and safety of pritelivir – an oral antiviral with the potential to reshape management of acyclovir-resistant HSV.
Herpes simplex infections are relatively uncommon in transplant recipients, but when they occur, they can be severe, persistent and highly morbid. Most patients are already receiving acyclovir prophylaxis, so breakthrough infections are frequently resistant. In this setting, treatment options are extremely limited. Existing therapies, such as foscarnet, are intravenous, toxic and often require hospitalisation. There has been a clear lack of safe, effective, orally bioavailable therapies for refractory HSV – this is precisely the gap pritelivir was designed to address.
PRIOH-1 was a multicentre, open-label, randomised phase III study in immunocompromised patients with refractory HSV infection. Refractory disease was defined as lack of improvement after at least seven days of appropriately dosed standard antiviral therapy, typically a nucleoside analogue.
Patients were randomized to receive either oral pritelivir or investigator’s choice therapy. In practice, the latter most commonly involved intravenous foscarnet, although other options such as cidofovir were permitted. Pritelivir was administered as a 400 mg loading dose on day one, followed by 100 mg daily.
The primary endpoint was complete lesion healing at day 28, defined as full epithelialisation of all lesions. Secondary endpoints included healing by day 42 and other clinically relevant outcomes such as hospitalisation.
The study met its primary endpoint, demonstrating clear superiority of pritelivir over investigator’s choice. Approximately 63% of patients in the pritelivir arm achieved complete lesion healing by day 28, compared with around 34% in the control arm. This represents a substantial improvement in outcomes for a population with otherwise limited treatment options.
Pritelivir addresses a critical unmet need. Its oral administration and favourable safety profile distinguish it from current therapies, particularly foscarnet, which is associated with nephrotoxicity, electrolyte imbalances and fluid overload.
Importantly, these data may prompt a shift in how we approach refractory HSV. Historically, escalation to agents like foscarnet has often been delayed until patients deteriorate significantly. With an effective oral option, clinicians may intervene earlier – at the first signs of treatment failure – potentially improving outcomes and quality of life.
HSV lesions in this population can be profoundly impactful: they are painful, disfiguring and can interfere with nutrition, hydration and psychological wellbeing. Earlier and more tolerable treatment could meaningfully reduce this burden.
While PRIOH-1 reflects real-world practice by allowing a range of comparator therapies, it will be important to see how pritelivir performs outside the clinical trial setting. Encouragingly, efficacy was consistent across patient subgroups, but post-approval real-world data will be key to confirming its broader impact.
About the European Society for Blood and Marrow Transplantation (EBMT)
The EBMT is a community of healthcare professionals, involved in clinical haematopoietic cell transplantation and cellular therapy, who share their experiences and develop co-operative studies. The EBMT has a governing body called the Board of Association and three sets of groups that channel the society’s research aims and other activities: the EBMT Working Parties, Committees, and Nurses Group, which addresses issues within the field specifically related to nursing.
This content has been developed in collaboration with the European Society for Blood and Marrow Transplantation for touchHEMATOLOGY. Views expressed are the speaker’s own and do not necessarily reflect the views of Touch Medical Media.
Disclosures: Genovefa Papanicolaou has no conflicts of interest to declare in relation to this article.
Cite: PRIOH-1: Pritelivir outperforms standard therapy in refractory HSV. touchHEMATOLOGY. 15th April 2026.
Interviewer: Caroline Markham
Related content
- FDA grants orphan drug status to zavabresib in myelofibrosis
- PARADIGM challenges role of intensive chemotherapy in newly diagnosed AML
- FDA grants orphan drug status to zavabresib in myelofibrosis
SIGN UP to touchHEMATOLOGY!
Join our global community today for access to thousands of peer-reviewed articles, expert insights and learn-on-the-go education across 150+ specialties, plus concise email updates and newsletters so you never miss out.
