Source: Health Products Regulatory Authority (ZA) Revision Year: 2021 Publisher: Equity Pharmaceuticals (Pty) Ltd., 100 Sovereign Drive, Route 21 Corporate Park, Nellmapius Drive, Irene, Pretoria
Pharmacological classification: A. 2.9 Other analgesics
ATC code: N02BG09
Methoxyflurane vapour possesses analgesic properties when inhaled at low concentrations. The precise mechanism of action whereby methoxyflurane produces analgesia at sub-anaesthetic doses is unknown, although a reduction in substance P- and β-endorphin-like immunoreactivity in the brain has been suggested.
After methoxyflurane administration, drowsiness may occur. The myocardium is minimally sensitised to epinephrine (adrenaline) by methoxyflurane. The blood pressure decreases in a dose dependant manner. This may be accompanied by bradycardia.
The blood pressure decrease noted is accompanied by reduced cardiac contractile force and reduced cardiac output.
Biotransformation of methoxyflurane occurs in man. As much as 50 to 70% of the absorbed dose is metabolised to free fluoride, oxalic acid, difluoro-methoxyacetic acid and dichloroacetic acid. Both the free fluoride and the oxalic acid can cause renal damage, which is dose-related.
Methoxyflurane diffuses into fatty tissues. Hence methoxyflurane is released slowly from this reservoir and becomes available for biotransformation for many days. Peak serum fluoride levels are seen 2 to 4 days after a dose.
About 60% of methoxyflurane uptake is excreted in the urine as organic fluorine, fluoride and oxalic acid; the remainder is exhaled unaltered or as carbon dioxide.
Studies have shown that higher peak blood fluoride levels are obtained earlier in obese than in nonobese and in the elderly.
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