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Dr. Bob is Robert Hsiung, MD,
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Posted by mogger on December 1, 2005, at 13:55:39
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
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
Posted by med_empowered on December 1, 2005, at 19:01:22
In reply to Re: zyprexa: 5mg, dopamine blocked?, posted by Tomatheus on December 1, 2005, at 15:58:10
hi! I also can't tell you exactly how much D2 blockage to expect. However, one interesting thing about antipsychotics is the *huge* variation from individual to individual. 5mgs/Zyprexa may have 70% or so D2 ocoupancy in some people with first-epsidoe psychosis (apparently, at around 70%, the D2 blockade is sufficient for antipsychotic use; at around 80%, EPS starts to pop up). However, other individuals may not get this sort of symptom-control until they reach 15-20+mgs/day. As an example...a BP I friend of mine takes Symbyax (the zyprexa plus prozac combo) as his primary treatment. He takes the 12/50 caps, which is 12mgs zyprexa, 50mgs prozac. He's had great results and few side effects. When I tried 2.5mgs/day zyprexa--one half of a 5mgs tab--I developed pronounced akakthisia.
Are you starting out on 5mgs/zyprexa? For depression, that strikes me as a bit high. Personally, I'd use a pill cutter to chop the pills in half (or fourths, if you'd prefer) and then adjust the zyprexa dose in small increments until you feel better, but still have minimal side effects. Also, some people dont take the antipsychotic during the entire treatment period...in years past, when the older antipsychotics were used to augment antidepressants (ex: perphenazine), it was pretty common for a patient to take a low-dose of the antipsychotic for a week or two, and then discontinue it once the symptoms of depression had improved. I think that's probably a strategy worth re-visiting with today's antipsychotics.
Anyway, as the other poster mentioned, part of the rationale of the antipsychotic augmentation seems to be that there can actually be an *increase* in levels of certain key neurotransmitters, rather than a decrease. This is definitely the case with Symbyax; the levels of dopamine, serotonin, and norepinephrine were all increased significantly while on Symbyax, much more so than with treatment with either Prozac alone or Zyprexa alone.
Posted by mogger on December 1, 2005, at 22:06:26
In reply to Re: zyprexa: 5mg, dopamine blocked?, posted by Tomatheus on December 1, 2005, at 15:58:10
Thanks so much for the info!
mogger
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