A Pilot Study on the Use of Methoxyflurane (Penthrox®) for Pain Control in the Emergency Department

Patients commonly visit the emergency department (ED) for pain after musculoskeletal injury and need early treatment with analgesic. Prompt and adequate pain relief can reduce suffering and promote early discharge and return to work. Nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids are the major injectable analgesic used for moderate to severe pain in EDs in Hong Kong. They are given via intravenous or intramuscular route for faster onset of action to achieve rapid pain relief in the emergency setting. However, injections are invasive and can be distressing for patients. Methoxyflurane (Penthrox®) is recently introduced to our emergency department as an inhalational analgesic. It has been granted registration approval in Hong Kong since 2018, but it is not widely used in the locality. Methoxyflurane is a volatile fluorinated hydrocarbon self-administrated by inhalation through a portable hand-held whistle-shaped inhaler device (Penthrox®) to relieve pain associated with trauma or minor surgical procedures in stable and conscious patients. In this study, the investigators will evaluate the efficacy and safety Penthrox® in the treatment of acute traumatic pain in hospital emergency department setting by comparing it to another conventional analgesic commonly used.


Eligibility Criteria:
Inclusion Criteria:

* Patients of both sexes from 18 to 64 years of age
* Presented to the ED in Ruttonjee Hospital for musculoskeletal injury within 72 hours of onset (Types of injury include contusion, sprain, crushing, burn, laceration, fracture and dislocation)
* Moderate pain at screening (10-point Numeric Rating Scale ≥4 to ≤7)

Exclusion Criteria:

* Critical or life-threatening condition requiring resuscitation
* Limb-threatening condition or any injuries requiring immediate management
* Hemodynamically unstable (systolic blood pressure \<90 mmHg, diastolic blood pressure \<60mmHg)
* Respiratory distress with respiratory rate \>20 breath per minute or oxygen saturation \<95% on room air
* Pregnant or breastfeeding women
* Impaired consciousness from any cause such as head injury and acute intoxication, based on the judgement of investigator
* Any physical, visual or cognitive conditions that may affect patient's ability to use visual analog scale for self-assessments of pain intensity
* Concomitant use of other analgesic within 5 hours (8 hours for diclofenac sodium) prior to presentation to ED
* Other pre-existing chronic pain condition
* Unable or refuse to provide written informed consent
* Unable to understand and converse in the language spoken
* Contraindication to inhalational methoxyflurane

  1. Known personal or family history of hypersensitivity to methoxyflurane or any fluorinated anesthetics
  2. Known pre-existing clinically significant renal or hepatic impairment
  3. Known personal or family history of malignant hyperthermia
  4. Concomitant use of nephrotoxic agents such as gentamicin, tetracycline, colistin, polymyxin B and amphotericin B
  5. Concomitant use of cytochrome P450 inducers such as alcohol, isoniazid, phenobarbital and rifampicin
* Contraindication to intramuscular ketorolac

  1. Known allergy to NSAIDS
  2. Known pre-existing clinically significant renal impairment or at risk for renal failure due to volume depletion
  3. Active major bleeding
  4. Suspected or confirmed cerebrovascular bleeding
  5. History of peptic ulcer disease, gastrointestinal bleeding or perforation
  6. Concomitant use of aspirin, other NSAIDS, anticoagulant or novel anticoagulant agent, pentoxifylline and probenecid
  7. Known bleeding disorders such as haemophilia, thrombocytopenia
  8. Heart failure
  9. Per-operative period of coronary artery bypass graft (CABG) surgery
  10. Concurrent asthmatic attack