Isoflurane and Methadone interaction
Isoflurane and Methadone: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Methadone (METHADOSE) label · effective 2026-04-27
Managing Risks from Concomitant Use with Benzodiazepines or Other CNS Depressants Concomitant use with benzodiazepines or other central nervous system (CNS) depressants, including alcohol, is a risk factor for respiratory depression and death [see Warnings and Precautions ( 5.2 )].
Reserve concomitant prescribing of benzodiazepines or other CNS depressants in patients in methadone treatment to those for whom alternatives to benzodiazepines or other CNS depressants are inadequate.
Concomitant use with benzodiazepines or other central nervous system (CNS) depressants, including alcohol, may result in profound sedation, respiratory depression, and death.
…with Methadone Concomitant use of methadone and benzodiazepines and/or other CNS depressants (e.g., alcohol, non-benzodiazepine sedative/hypnotics, anxiolytics, tranquilizers, muscle relaxants, general anesthetics, antipsychotics, gabapentinoids [gabapentin or pregabalin], and other opioids), increases the risk of adverse reactions including overdose and death.
In others, gradually tapering a patient off a prescribed benzodiazepine or other CNS depressant or decreasing to the lowest effective dose may be appropriate.
From the Isoflurane (FORANE) label · effective 2024-12-09
Monitor QT interval when administering FORANE to susceptible patients (e.g., patients with congenital Long QT Syndrome or patients taking drugs that can prolong the QT interval).
• Concomitant use of N 2 O and/or opioids reduces the MAC of FORANE.
Opioids Opioids decrease the Minimum Alveolar Concentration (MAC) of FORANE.
In general, anesthetic concentrations of FORANE at equilibrium reduce the ED 95 of succinylcholine, atracurium, pancuronium, rocuronium and vecuronium by approximately 25 to 40% or more compared to N 2 O/opioid anesthesia.
Opioids such as fentanyl and its analogues, when combined with FORANE, may lead to a synergistic fall in blood pressure and respiratory rate.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.