Posted by Tomatheus on December 1, 2005, at 15:58:10
In reply to zyprexa: 5mg, dopamine blocked?, posted by mogger on December 1, 2005, at 13:55:39
Mogger,
I'm by no means an expert in this area, but I'll do my best to try to answer your question based on some of the limited research I've done.
To my knowledge, all of the biochemical tests involving Zyprexa have been done in rats, so I don't think one can really say with 100 percent certainty how strongly Zyprexa blocks dopamine receptors in humans. And actually, even though antipsychotics are known primarily for their blockade of dopamine receptors, the actions Zyprexa (an "atypical" antipsychotic) are believed to be a lot more complex than that. My information in a recent post (http://www.dr-bob.org/babble/20051126/msgs/584151.html) about Zyprexa's blockade of the D1 and D2 receptors actually came from a relatively old study done by Eli Lilly and Co. (Moore et al., 1992). It was also reported in this study that Zyprexa was believed to block a serotonin receptor (5HT2) and possess anticholinergic properties. More recently, evidence has emerged that Zyprexa not only blocks D1, D2, and 5HT2 receptors, but also D3, D4, 5HT6, M1 muscarinic, and alpha 1-adrenergic receptors (Bymaster et al., 1999). To make matters even more complicated, microdialysis studies have shown that the administration of Zyprexa actually increased extracellular dopamine and norepinephrine levels in the prefrontal cortex, and increased extracellular dopamine (but not norepinephrine) levels in the neostriatum and nucleus accumbens (Bymaster et al., 1999). And finally, as much as the information I've provided demonstrates the complexity of Zyprexa's actions, keep in mind that I'm no expert and may be missing even more information.
So, in terms of Zyprexa's ability to augment SSRIs, the drug's mechanisms of action are so multifaceted that it's difficult (especially for patients like us) to understand the relative contributions of all of Zyprexa's effects and how some of these effects may serve to augment SSRIs. Being the amateur patient that I am, I sort of get the impression that because Zyprexa is first and foremost an antipsychotic, its strongest mechanism of action is its blockade of the dopamine receptors. But that's just an educated guess, so I could be way off. It's also important to remember that different psychiatric patients are believed differ from one another in terms of brain chemistry, so even though the addition of Zyprexa to an SSRI may serve to augment its effects in one patient, it could potentially be detrimental in a different patient.
So, I'm not sure how well this answers your question, but take it for what it's worth.
Tomatheus
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REFERENCES
Bymaster, F., Perry, K. W., Nelson, D. L., Wong, D. T., Rasmussen, K., Moore, N. A., et al. (1999). Olanzapine: A Basic science update. British Journal of Psychiatry Supplement, 37, 36-40.
Moore, N. A., Tye, N. C., Axton, M. S., & Risius, F.C. (1992). The behavioral pharmacology of olanzapine, a novel "atypical" antipsychotic agent. Journal of Pharmacology and Experimental Therapeutics, 262, 545-51.
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> Hi there,
> I am on 5mg of Zyprexa and was wondering if anyone knew whether Zyprexa blocks a lot of dopamine at that dose? How does it augment an SSRI (I am on 200mg of zoloft) if it blocks dopamine? Many thanks, I am clueless in this subject,
> mogger
poster:Tomatheus
thread:584237
URL: http://www.dr-bob.org/babble/20051126/msgs/584253.html