Trial on Efficacy and Safety of Pritelivir Tablets for Treatment of Acyclovir-resistant Mucocutaneous HSV (Herpes Simplex Virus) Infections in Immunocompromised Subjects

The trial comprises 5 Parts, Part A, B, C, D, E and F. Part A and Part B (Phase 2) have been finalised. * Part A is a randomized, open-label, multi-center, comparative design to assess the efficacy and safety in subjects with ACV-resistant mucocutaneous HSV infection, treated with oral pritelivir or intravenous foscarnet. * Part B is an open-label, multi-center design to assess the efficacy and safety of pritelivir in subjects with ACV-resistant-mucocutaneous HSV and who either: 1. present with foscarnet-resistance/intolerance, or 2. developed foscarnet resistance/intolerance during treatment in Part A (no improvement after at least 5 days of foscarnet therapy or intolerance to foscarnet requiring cessation of foscarnet treatment). Parts C, D, E and F (Phase 3). * Part C is a randomized, open-label, multi-center, comparative design to assess the efficacy and safety of oral pritelivir in subjects with acyclovir resistent (ACV-R) mucocutaneous HSV episodes. Subjects with ACV-R mucocutaneous HSV infection will be randomized 1:1 to receive either oral pritelivir or Investigator's Choice. This trial part is designed to show superiority of pritelivir against Investigator's Choice in obtaining clinical cure, ie, number of subjects with all lesions healed within 28 days. * Part D is an open-label, multi-center design to assess the efficacy and safety of pritelivir in subjects with ACV-R mucocutaneous HSV episodes and who in addition either: 1. present with iv foscarnet resistance/intolerance already at Screening for inclusion, or 2. developed foscarnet resistance/intolerance during treatment in Part C (no improvement after at least 7 days of foscarnet treatment or intolerance to foscarnet requiring cessation of foscarnet treatment). Part D has been closed in June 2022. * Part E is an open-label, multi-center design to assess the safety and efficacy of pritelivir in subjects with acyclovir susceptible (ACV-S) mucocutaneous HSV episodes, (Part E is not being conducted in Germany). * Part F is an open-label, multi-center design to assess the efficacy and safety of pritelivir in subjects with ACV-R mucocutaneous HSV episodes and who in addition either: 1. present with iv foscarnet resistance/intolerance already at Screening for inclusion, or 2. developed foscarnet resistance/intolerance during treatment in Part C (no improvement after at least 7 days of foscarnet treatment or intolerance to foscarnet requiring cessation of foscarnet treatment). 3. cannot be enrolled into Part D anymore because enrollment into Part D has been completed. Dosing of trial medication: Pritelivir oral tablet as single daily doses of 100 mg (following a loading dose of 400 mg as first dose) Comparator per investigator's choice (provided the drug listed below is nationally approved): Foscarnet intermittent infusions of 40 mg/kg every 8 hours or 60 mg/kg every 12 hours (to be adjusted in case of renal impairment) for a minimum of 1 hour duration, or Cidofovir iv infusion of 5 mg/kg body weight given once weekly, or Cidofovir 1% or 3% topical treatment, applied 2 to 4 times daily, or Imiquimod 5% topical treatment, 3 times per week. Duration of treatment: Until all mucocutaneous HSV lesions are healed or up to 28 days, whichever is earlier. A prolongation up to a maximum of 42 days may be possible depending on the clinical progress.