Herpes simplex virus (HSV) is frequently detected in the respiratory tract of mechanically ventilated patients and is associated with a worse outcome. The aim of this study is to determine whether antiviral therapy in HSV-positive patients improves outcome. Prospective, multicentre, open-label, randomised, controlled trial in parallel-group design. Adult, mechanically ventilated patients with pneumonia and HSV type 1 detected in bronchoalveolar lavage (≥105 copies/mL) are eligible for participation and will be randomly allocated (1:1) to receive acyclovir (10 mg/kg body weight every 8 hours) for 10 days (or until discharge from the intensive care unit if earlier) or no intervention (control group). The primary outcome is mortality measured at day 30 after randomisation (primary endpoint) and will be analysed with Cox mixed-effects model. Secondary endpoints include ventilator-free and vasopressor-free days up to day 30. A total of 710 patients will be included in the trial.
