cross tolerance of methadone and meperidine

[anhalonium9]

when i was in the hospital once, i was given a "shot" of demerol while on a maintenance dose of 80 mgs. methadone. to my suprise i got high as a kite. never could figure it out. then i read something that said methadone exhibits incomplete and variable cross tolerance with other opioids.

anyone?

 

[BilZ0r]

Interesting... well methadone definately induces some form of cross tolerance or morphine and heroin, but your right, it is often reported to be incompletely cross tolerant..

I can't think of anything that explains it, though my geuss would be something to do with methandone being relatively selective for the Mu receptor, and meperidine being non-selective, as well as possibley effecting non-opioid receptors.

 

[anhalonium9]

does non-selective mean affinity for more than just mu receptors?

 

[fastandbulbous]

Methadone has NMDA antagonist activity as well (too tired to work out how that'll alter things), but NMDA antagonists can slow down/reverse opiaye tolerance

 

[BilZ0r]

yes, non-selective means it hits up more than one receptor.