Self-administered, inhaled methoxyflurane improves patient comfort during nasoduodenal intubation for computed tomography enteroclysis for suspected small bowel disease: a randomized, double-blind, placebo-controlled trial

The role of inhaled methoxyflurane in acute pain management

Methoxyflurane is an inhaled analgesic administered via a disposable inhaler which has been used in Australia for over 40 years for the management of pain associated with trauma and for medical procedures in children and adults. Now available in 16 countries worldwide, it is licensed in Europe for moderate to severe pain associated with trauma in conscious adults, although additional applications are being made to widen the range of approved indications. Considering these ongoing developments, we reviewed the available evidence on clinical usage and safety of inhaled analgesic methoxyflurane in trauma pain and in medical procedures in both adults and children. Published data on methoxyflurane in trauma and procedural pain show it to be effective, well tolerated, and highly rated by patients, providing rapid onset of analgesia. Methoxyflurane has a well-established safety profile; adverse events are usually brief and self-limiting, and no clinically significant effects on vital signs or consciousness levels have been reported. Nephrotoxicity previously associated with methoxyflurane at high anesthetic doses is not reported with low analgesic doses. Although two large retrospective comparative studies in the prehospital setting showed inhaled analgesic methoxyflurane to be less effective than intravenous morphine and intranasal fentanyl, this should be balanced against the administration, supervision times, and safety profile of these agents. Given the limitations of currently available analgesic agents in the prehospital and emergency department settings, the ease of use and portability of methoxyflurane combined with its rapid onset of effective pain relief and favorable safety profile make it a useful nonopioid option for pain management. Except for the STOP! study, which formed the basis for approval in trauma pain in Europe, and a few smaller randomized controlled trials (RCTs), much of the available data are observational or retrospective, and further RCTs are currently underway to provide more robust data.

A review of the safety and efficacy of inhaled methoxyflurane as an analgesic for outpatient procedures

Methoxyflurane delivered via a hand-held inhaler is a proven analgesic which has been used in Australasia for emergency relief of trauma associated pain since the 1970s. The agent is self-administered by the patient under the supervision of trained personnel. More than 5 million patients have received inhaled methoxyflurane without significant side effects. Methoxyflurane is also licensed in Australasia for the relief of pain in monitored conscious patients requiring analgesia for minor surgical procedures. Recent clinical studies undertaken in a variety of outpatient settings, including colonoscopy, prostate biopsy, dental procedures, bone marrow biopsy, and the management of burns dressings, indicate that inhaled methoxyflurane has significant analgesic activity, without producing deep sedation or respiratory depression. Return to full psychomotor activity is rapid. Thus, methoxyflurane may be a suitable and well-tolerated alternative to traditional i.v. sedative agents for outpatient medical and surgical procedures. There are direct advantages to the patient in terms of rapid recovery and an early return to normal activities, and significant benefits for outpatient departments in terms of cost saving and rate of throughput. Further randomised controlled trials comparing the efficacy, safety, and cost-effectiveness of inhaled methoxyflurane against traditional i.v. sedative techniques are currently in progress.

Psychomotor and cognitive effects of 15-minute inhalation of methoxyflurane in healthy volunteers: implication for post-colonoscopy care

Background and study aims: Colonoscopy with portal inhaled methoxyflurane (Penthrox) is highly feasible with low sedation risk and allows earlier discharge. It is unclear if subjects can return to highly skilled psychomotor skill task shortly after Penthrox assisted colonoscopy. We evaluated the psychomotor and cognitive effects of 15-minute inhalation of Penthrox in adults. Patients and methods: Sixty healthy volunteers (18 to 80 years) were studied on 2 occasions with either Penthrox or placebo in a randomized, double-blind fashion. On each occasion, the subject's psychomotor function was examined before, immediately, 30, 60, 120, 180 and 240 min after a 15-minute inhalation of studied drug, using validated psychomotor tests (Digit Symbol Substitution Test (DSST), auditory reaction time (ART), eye-hand coordination (EHC) test, trail making test (TMT) and logical reasoning test (LRT). Results: Compared to placebo, a 15-minute Penthrox inhalation led to an immediate but small impairment of DSST (P < 0.001), ART (P < 0.001), EHC (P < 0.01), TMT (P = 0.02) and LRT (P = 0.04). In all subjects, the performance of all 5 tests normalized by 30 minutes after inhalation, and was comparable to that with placebo. Although increasing age was associated with a small deterioration in psychomotor testing performance, the magnitude of Penthrox effects remained comparable among all age groups. Conclusions: In all age groups, a 15-minute Penthrox inhalation induces acute but short-lasting impairment of psychomotor and cognitive performance, which returns to normal within 30 minutes , indicating that subjects who have colonoscopy with Penthrox can return to highly skilled psychomotor skills tasks such as driving and daily work the same day.

Self-administered methoxyflurane for procedural analgesia: experience in a tertiary Australasian centre

Methoxyflurane, an agent formerly used as a volatile anaesthetic but that has strong analgesic properties, will soon become available again in the UK and Europe in the form of a small hand-held inhaler. We describe our experience in the use of inhaled methoxyflurane for procedural analgesia within a large tertiary hospital. In a small pilot crossover study of patients undergoing burns-dressing procedures, self-administered methoxyflurane inhalation was preferred to ketamine-midazolam patient-controlled analgesia by five of eight patients. Patient and proceduralist outcomes and satisfaction were recorded from a subsequent case series of 173 minor surgical and radiological procedures in 123 patients performed using inhaled methoxyflurane. The procedures included change of dressing, minor debridement, colonoscopy and incision-and-drainage of abscess. There was a 97% success rate of methoxyflurane analgesia to facilitate these procedures. Limitations of methoxyflurane include maximal daily and weekly doses, and uncertainty regarding its safety in patients with pre-existing renal disease.

The risk of unblinding was infrequently and incompletely reported in 300 randomized clinical trial publications

OBJECTIVES

To assess the proportion of clinical trials explicitly reporting the risk of unblinding, to evaluate the completeness of reporting on unblinding risk, and to describe the reported procedures involved in assessing unblinding.

STUDY DESIGN AND SETTING

We sampled at random 300 blinded randomized clinical trials indexed in PubMed in 2010. Two authors read the trial publications and extracted data independently.

RESULTS

Twenty-four trial publications, or 8% (95% confidence interval [CI], 5, 12%), explicitly reported the risk of unblinding, of which 16 publications, or 5% (95% CI, 3, 8%), reported compromised blinding; and 8 publications, or 3% (95% CI, 1, 5%), intact blinding. The reporting on risk of unblinding in the 24 trial publications was generally incomplete. The median proportion of assessments per trial affected by unblinding was 3% (range 1-30%). The most common mechanism for unblinding was perceptible physical properties of the treatments, for example, a difference in the taste and odor of a typhoid vaccine compared with its placebo.

CONCLUSION

Published articles on randomized clinical trials infrequently reported risk of unblinding. This may reflect a tendency for avoiding reporting actual or suspected unblinding or a genuine low risk of unblinding.