GREEN WHISTLE - METHOXYFLURANE (PENTHROX): AN OPIOID SUBSTITUTE?

[IceWizard]

MIKE RUBIN MD, FACEP FAAEM

Attending Physician
Department of Emergency Medicine
University of Ottawa School of Medicine




PAIN MANAGEMENT STRATEGIES IN THE ED



STOPIOID is a free open access medical education (FOAMed)
resource for health care providers. Postings are evidence based,
with a focus on multi-modal approaches to pain management
and opioid harm reduction. This resource explores methods to
curtail the opioid epidemic while providing appropriate pain control.



GREEN WHISTLE
-
METHOXYFLURANE (PENTHROX):
AN OPIOID SUBSTITUTE?


October 11, 2018
Green Whistle,
Inhalational Anaesthetic,
Methoxyflurane,
Opioid Sparing,
Penthrox,
Procedural Analgesia



Green Whistle - Penthrox Inhaler



Methoxyflurane (Penthrox) is a halogenated ether first used clinically as a volatile
inhalational anaesthetic. It has been used as an analgesic in Australia for the past
30 years (1) and is now available in Europe and Canada as well.

Penthrox is a self-administered, rapid acting analgesic agent for short-term pain relief.
The Penthrox inhaler is a green whistle shaped single use device that delivers
methoxyflurane in analgesic doses. Patients are able to assess their own level of pain
and titrate the amount of Penthrox inhaled for adequate pain control. Continuous
inhalation provides analgesic relief for up to 25-30 minutes, or approximately 1 hour
when administered intermittently. Patients should be advised to take the lowest possible
dose to achieve pain relief (7).

Studies of low-dose methoxyflurane as an analgesic agent show decreases in pain scores
and indicate that methoxyflurane is an efficacious analgesic in the ED and pre-hospital
settings (2) and for procedural analgesia (3).

In a multicentre, randomized, double-blind, placebo-controlled trial of trauma patients
in the ED, methoxyflurane resulted in significantly greater reduction in pain scores and
less need for rescue medication, with initial onset of pain relief occurring at a median
of 4 min (4).

Penthrox may eliminate the need for opioid analgesia for dislocations or fractures, for
example, since the pain relief from Penthrox with or without the addition of simple
non-opioid analgesia, may be sufficient for reduction or splinting (5).

Although methoxyflurane is known to be potentially nephrotoxic at anaesthetic doses,
the much lower doses used for pain relief are not associated with nephrotoxicity or an
increased risk of renal disease (6). Methoxyflurane is contraindicated in patients with
significant renal impairment, prior history of liver dysfunction following halogenated
anesthetic use and susceptibility to malignant hyperthermia.

Inhaled methoxyflurane may offer advantages over other analgesics administered via
the intravenous, intramuscular or intranasal routes in terms of its non-invasive
self-administration, ease of use and/or rapid onset of action (1). As such, this
medication can theoretically improve analgesia while reducing the need for
opioids in the ED.



References:


01 Blair, H.A. & Frampton, J.E. Methoxyflurane: A Review in Trauma Pain.
Clin Drug Investig (2016) 36: 1067.

02 Grindlay J, Babl FE. Review article: efficacy and safety of methoxyflurane
analgesia in the emergency department and prehospital setting.
Emerg Med Australas. 2009;21:4–11.

03 Gaskell AL, Jephcott CG, Smithells JR, Sleigh JW. Self-administered
methoxyflurane for procedural analgesia: experience in a tertiary
Australasian centre. Anaesthesia. 2016;71:417–23.

04 Coffey F, Wright J, Hartshorn S, et al STOP!: a randomised, double-blind,
placebo-controlled study of the efficacy and safety of methoxyflurane for
the treatment of acute pain Emerg Med J 2014;31:613-618.

05 Coffey, F., Dissmann, P., Mirza, K. et al. Methoxyflurane Analgesia in
Adult Patients in the Emergency Department: A Subgroup Analysis of a
Randomized, Double-blind, Placebo-controlled Study (STOP!)
Adv Ther (2016) 33: 2012.

06 Dayan AD. Analgesic use of inhaled methoxyflurane: evaluation of its
potential nephrotoxicity. Hum Exp Toxicol. 2016;35:91–100.

07 Methoxyflurane (Penthrox). Product Monograph. Purdue Pharma. April 6, 2018.