Background: This first-in-human volunteer phase I clinical trial aimed to evaluate the safety, tolerability, and anesthesia efficacy of emulsified isoflurane (EI), an intravenously injectable formulation of isoflurane.
Methods: Seventy-eight healthy volunteers were recruited in this open-label, single-bolus, dose-escalation, phase I trial and were allocated into 16 cohorts. Each volunteer received a single bolus injection of EI. The dose started with 0.3 mg/kg (for isoflurane) and was planned to end with 64.6 mg/kg. Postdose vital signs, physical examination, laboratory tests, chest radiograph, 12-lead electrocardiogram, and development of any adverse event were closely monitored as safety measurements. Effectiveness in producing sedation/anesthesia was assessed by Modified Observer's Assessment of Alertness/Sedation and Bispectral Index.
Results: The dose escalation ended as planned. The most common adverse events associated with EI were injection pain (77 of 78, 98.7%) and transient tachycardia (22 of 78, 25.6%). Only at high doses (≥38.3 mg/kg) did EI cause transient hypotension (5 of 78, 6.4%) or apnea (11 of 78, 14.1%), but all the affected volunteers recovered uneventfully. Fast onset of unconsciousness (typically 40 s after injection) was developed in all volunteers receiving doses of 22.6 mg/kg or greater. Waking-up time and depression in Modified Observer's Assessment of Alertness/Sedation correlated well with EI dose. None of the postdose tests revealed any abnormal result.
Conclusions: EI is safe for intravenous injection in human volunteers in the dose range of 0.3 to 64.6 mg/kg. At doses of 22.6 mg/kg or higher, EI produced rapid onset of unconsciousness in all volunteers followed by fast, predictable, and complete recovery.