http://www.pharmamedix.com/principiovoc ... rmacologiaLa ketamina (o chetamina; INN: ketamine) è un anestetico generale, non barbiturico, ad azione rapida, ottenuto a partire dalla fenciclidina (PCP). E’ disponibile sotto forma di miscela racemica, contenente uguali quantità dei due isomeri: (S+) ketamina e (R-) ketamina. La (S+) ketamina è caratterizzata da una potenza analgesica pari a 3-4 volte quella dell’isomero (R-).
La ketamina possiede elevata attività analgesica, associata però ad intensi effetti collaterali, soprattutto causati dalla stimolazione del sistema cardiovascolare. L’azione analgesica dell’enantiomero (S+) ketamina è risultata maggiore nell’uomo rispetto alla donna. Nella donna infatti la clearance del farmaco aumenta di circa il 20%, condizione che comporta, a parità di dosaggio, una concentrazione plasmatica di ketamina significativamente più elevata nei pazienti di sesso maschile (Sigtermans et al., 2009). L’azione analgesica si manifesta a dosi subanestetiche per inibizione acompetitiva dei recettori NMDA del glutammato.
http://www.bluelight.org/vb/threads/447 ... mine/page6fairnymph ha scritto:Most ketamine is racemic, i.e. it is composed of equal parts S/(+) and R/(-) ketamine. The (+) isomer of ketamine is more potent than the (-) isomer. It also seems that (+) ketamine would be superior as a psychedelic tool, for a number of reasons.
Some facts/differences worth noting:
In a study which used male adults, the amount of ketamine needed for total anaesthesia was ~271 mg (+) ketamine vs ~409 mg racemic ketamine. [1]
(+) ketamine is generally considered to be approx. 2-3 times more potent than (-) ketamine.[3]
(+) ketamine is cleared from the body in HALF the time it takes for racemic ketamine. The clearance of (-) ketamine takes only slightly longer than racemic ketamine.[1]
(-) ketamine significantly inhibits the clearance of (+) ketamine. This means that if you have pure (+) ketamine, after you come out of a k-hole, the aftereffects of the k will wear off more quickly than they would if you had done racemic ketamine.[1]
(+) ketamine inhibits the dopamine transporter 8 times more potently than (-) ketamine.[2]
However, application of S(+)-ketamine was associated with a remarkably smoother emergence period, a profound postoperative analgesia, a more rapid recovery of cerebral functions, and a greater preference by the study persons. The incidence of psychotomimetic phenomena appeared to be negligibly less after S(+)-ketamine in comparison to racemic ketamine, but their quality was described as far less unpleasant. Clinical use of S(+)-ketamine administered at one-half of the usual dose is thus not only associated with a reduction of undesirable adverse effects without altering ketamine's anaesthetic and analgesic potency, but also offers distinctive improvements due to the reduced drug load. Moreover, increasing experimental evidence supports a remarkable neuroprotective effect of S(+)-ketamine, which may become a promising drug for new therapeutic approaches to neuroprotection.[3]
It was found that , and that at these concentrations (R)-ketamine interacts also weakly with the sigma receptor sites, where (S)-ketamine binds only negligibly....R)-ketamine did not produce psychotic symptoms, but a state of relaxation. The (S)-ketamine-induced metabolic hyperfrontality appears to parallel similar metabolic findings in acute psychotic schizophrenic patients and encourages further investigations of glutamatergic disturbances in schizophrenia.
This leads me to believe that the psychedelic effects of racemic ketamine are being produced by the (+) isomer. This would further lead me to conclude that pure (+) ketamine would be more psychedelic in its subjective effects -- as well as less sedating (as noted in the study). [4]
With sub-anaesthetic doses of ketamine in humans, 50% of the test subjects who took racemic ketamine experienced anterograde amnesia (could not remember portions of the k-experience) , while only 8% of those who took (+) ketamine experienced amnesia. This means that your ability to recall a ketamine trip would be greatly improved if you were taking pure (+) ketamine. [5]
Subjective mood was judged by the volunteers to be significantly better after S-(+)-ketamine, and volunteers found S-(+)-ketamine to be more acceptable than racemic ketamine. The frequency of dreams was the same after both drugs. No unpleasant dreams were reported after S-(+)-ketamine, but one of the volunteers who received racemic ketamine had uncomfortable dreams. It seems that (+) ketamine has a distinct positive vibe to it, unlike racemic ketamine which is more neutral (or even negative) in its psychological effects. [6]
http://www.bluelight.org/vb/threads/447 ... mine/page6daytripper10 ha scritto:So there seems to be a lot of debate about the s+, racemic, and r- isomers of ketamine.
Recently SWIMs source changed and went from the shard crystals (green box) to the other kind of crystals (red box).
http://farm5.static.flickr.com/4064/470 ... c7a6_b.jpg
The effects are totally different. The shard crystal k-hole was clean and memorable, not confusing and uncomfortable. The shard crystal ketamine left your mind still able to think, able to read (whereas the new one makes you have to close one eye to read things on the computer screen.) The shards seem much cleaner and the k-holes more interesting and memorable.
Is this correlated to the s+/r- isomer difference? Any thoughts?
La mia esperienza con due batch diversi:
Primo batch
Venduto come: "Ketamina indiana"
Aspetto: Cristalli aghiformi molto piccoli
Metodo d'assunzione: IM
Salita: Lenta e lineare
Effetto: Lucido seppur dissociato. Lo stato mentale sembra sovraeccitato
Potenza percepita: Normale, simile a quella farmaceutcia
Discesa: Abbastanza veloce e pulita
Hangover: Poco invadente
Commento finale: Probabilmente un racemo
Secondo batch
Venduto come: "Isomero (S)+"
Aspetto: Cristalli granulari di media grandezza (molto simili ai cristalli sulla destra nel post sopracitato)
Metodo d'assunzione: IM
Salita: Abbastanza rapida, come una nube scura che mi avvolge
Effetto: Confuso e dissociato, molto simile alla MXE (per un attimo ho pensato fosse un batch sbagliato)
Potenza percepita: Piu' forte di quella farmaceutica
Discesa: Lunga e tortuosa (al risveglio ero ancora avvolto nel torpore chimico)
Hangover: Piuttosto evidente e lungo
Commento finale: Forse era l'isomero (S)+?
Pur non avendo alcuna certezza riguardo ai batch, cos'e' che non torna? Come descritto nel secondo post che ho citato, l'isomero (S)+ dovrebbe avere una discesa piu' rapida e dovrebbe innescare un'esperienza meno intensa. Inoltre un racemo dovrebbe provocare un hangover piu' fastidioso.
Che cosa ne pensate? Avete esperienze a riguardo?
ATTENZIONE: Assumere ketamina in cristalli via IM e' pericoloso per tutta una serie di motivi. Consiglio a tutti di leggere questo mio post: http://forum.psiconauti.net/viewtopic.php?p=5191#p5191
