Inhaled analgesic (fluorinated volatile anaesthetic) Inhaled
Methoxyflurane
Methoxyflurane
CPG Reference
Authorised Medications — Methoxyflurane (Penthrox)
Indications
- ✓ Analgesia
Contraindications
- ✕ Hypersensitivity to fluorinated anaesthetics
- ✕ Children under 1 year of age
- ✕ Patients who are unable to understand or co-operate including those affected by alcohol or illicit drugs
- ✕ Patients with a severe head injury and altered state of consciousness
- ✕ Patients susceptible to malignant hyperthermia
Precautions
- ⚠ Monitor for over-sedation and apnoea, particularly in children under 5
- ⚠ Equipment required: Penthrox® Inhaler Device with charcoal filter attached
- ⚠ Renal impairment: renal toxicity in high doses; may worsen declining renal function
- ⚠ Children under 5 may require assistance using the device
- ⚠ Elderly: possible reduction in blood pressure or heart rate
Dosing
Adult
Amount 3 mL vaporized in a Penthrox® Inhaler device
Route Inhaled — patient self-administers via Penthrox® Inhaler
Repeat Inhaled intermittently to maintain adequate analgesia; repeat if necessary after 30 minutes
Max dose 6 mL daily; maximum 5 doses (15 mL) per week; not recommended on consecutive days
Patient must be able to self-administer. Do NOT attach inhaler to oxygen source. Onset of pain relief after 6–10 inhalations. Secure used or partially used Penthrox® inhaler and vial in supplied plastic bag for disposal.
Paediatric (>1 year old)
Amount 3 mL vaporized in a Penthrox® Inhaler device
Route Inhaled — patient self-administers via Penthrox® Inhaler
Repeat Inhaled intermittently to maintain adequate analgesia; repeat if necessary after 30 minutes
Max dose 6 mL daily; maximum 5 doses (15 mL) per week; not recommended on consecutive days
Children under 5 may require assistance using the device. Monitor closely for over-sedation and apnoea. Patient must be able to understand and co-operate with self-administration.
Onset: Pain relief after 6–10 inhalations
Side Effects & Notes
Side Effects
- • Cough (initial dose — advise patient to inhale gently)
- • Dizziness
- • Drowsiness
- • Headache
- • Dry mouth
- • Disinhibition
Clinical Notes
- → Monitoring required post-administration: pain score
- → Patient must be able to self-administer the inhaler — do not administer to patients who cannot understand or co-operate, including those affected by alcohol or illicit drugs
- → Do NOT attach the Penthrox® inhaler to an oxygen source
- → Attach the charcoal filter to the diluter hole before use
- → To increase analgesic concentration, patient can block the diluter hole on the carbon filter
- → Ensure sufficient ventilation when the Penthrox® inhaler is in use
- → Concurrent use of multiple pain-relieving strategies (pharmacological and non-pharmacological) provides superior pain relief compared to any single approach
- → Secure used or partially used Penthrox® inhaler and vial in the supplied plastic bag for disposal
- → In the context of Chest Pain/ACS: administer Methoxyflurane if pain remains >3/10 after the first spray of GTN