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Comment by lordlic | Hacker News Reader

If you IV a single 24mg/kg dose like the sheep in the study, I suspect you won't be experiencing anything at all before you lose consciousness.

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Concur. Standard IV dose in humans for general anesthesia is 0.5-1.0 mg/kg. (I'm a retired neurosurgical anesthesiologist who used ketamine for GA in around 500 patients over 38 years, and smaller IV/IM doses in perhaps 1,000 more individuals)

I was confused by how low that was until I realized you meant per minute. I assume you use a higher dose at first to actually induce unconsciousness?

No, I did NOT mean per minute. Ketamine dose for induction of unconsciousness/general anesthesia is 0.5-1.0 mg/kg as a bolus push over a few seconds. Ketamine comes as 100mg/cc and 10mg/cc: I always used the 10mg/cc formulation IV because it was easier to draw up the precise dose I wanted. Loss of consciousness takes 30 seconds to 1 minute for most people. I never used ketamine drips during anesthesia because it was just one more thing to have to track. Boluses every 30-60 minutes sufficed.

For IM use in children and patients with no venous access, induction of general anesthesia is achieved with a dose of 5-10mg/kg. Here, the 100mg/cc formulation is superior since the volume to be injected is 1/10 that required with the 10mg/cc version.

Addendum: one of ketamine's most common uses is in the Burn Unit, as the general anesthetic of choice for daily burn dressing changes, which often require daily doses for weeks. Most people receiving daily doses become tolerant within a few days, such that the dose has to steadily be increased over the period of treatment. A log book of dates and doses is kept at the patient's bedside because different people will be doing the dressing changes on different days.

For example, if on the first day the dose was a bolus of 1.0 mg/kg IV, and by the fourth or fifth day the patient wasn't rendered unconscious by this dose, a supplemental dose of perhaps 0.5 mg/kg IV would be given there and then, and the next day's starting dose would be 1.5 mg/kg. Sometimes patients would end up receiving 2-3 times their starting dose by the time the series of dressing changes was complete.

That seems kinda low. I've personally never seen anyone get knocked out by a single bolus < 1mg/kg. The only citation I can find is 0,5-2,0 mg/kg if primed with midazolam which sounds more reasonable but is still a big caveat.

A lot of doses < 1 mg/kg are used in e.g. caudal blocks https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4258981/

How many people have you personally never seen get knocked out by a single bolus < 1mg/kg?

Ah, I see. I was conflating the IM and IV dosages; 0.5mg/kg seemed much too low to induce general anesthesia from what I vaguely remembered of IM dosages. Thank you for elaborating.

Have you heard of ketamine making people "immune" to alcohol and other drugs like hallucinogens?

If you want to geek out over the pharmacology, ketamine is mainly an NMDA antagonist, same as the other dissociative hallucinogens, and apparently that's one of the mechanisms of ethanol too, though anecdotally I've only heard complaints about alcohol cross-tolerance issues with GABA agonists.

This whole subject is really interesting and you should at least check out some Wikipedia articles:

https://en.wikipedia.org/wiki/NMDA_receptor_antagonist

https://en.wikipedia.org/wiki/Alcohol_(drug)#Pharmacology

https://en.wikipedia.org/wiki/Receptor_(biochemistry)

Thank you, also to bookofjoe for the answers.

I had found the NMDA receptor connection, but so far not any mention of long term (four to six months) of alcohol insensitivity after ketamine use. If there is one, I'm unable to find it.

Some new information in those Wikipedia links, about other neuroreceptors.

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