Comparison of inhalational methoxyflurane (Penthrox®) and intramuscular tramadol for prehospital analgesia

INTRODUCTION Treatment of pain is an important component of prehospital care. Inhalational analgesia agents have attractive strengths, but there is a paucity of studies comparing these with more conventional agents. We aimed to compare inhalational methoxyflurane and intramuscular (IM) tramadol as first-contact analgesia in the Singapore national ambulance service. METHODS Ambulances were randomised to carry either methoxyflurane or IM tramadol for the first six months and crossed over to the other arm after six months. Patients aged >= 16 years, with acute pain arising from musculoskeletal trauma with Numerical Rating Scale (NRS) score >= 3 were enrolled. Variables included NRS reduction, time variables, adverse effects, Ramsay Sedation Scores, and patient and paramedic satisfaction scores on a Likert scale. RESULTS A total of 369 patients were enrolled into this study, but 26 patients were excluded due to missing data. The methoxyflurane arm had a shorter median time taken from arrival at the scene to drug administration (9.0 [interquartile range 6.0-14.0] minutes vs. 11.0 [interquartile range 8.0-15.0] minutes). For patients who achieved reduction in NRS >= 3 within 20 minutes, those in the methoxyflurane arm took a shorter time. However, the methoxyflurane (46.7%) arm experienced lower proportion of patients not achieving NRS reduction >= 3 when compared to the tramadol (71.6%) arm after over 20 minutes. The methoxyflurane arm had significantly higher paramedic and patient satisfaction scores. CONCLUSION For the doses of medication used in this implementation study, methoxyflurane was superior in efficacy, speed of onset and administration, but had more minor adverse effects when compared to IM tramadol.