Posted by SLS on March 15, 2002, at 18:09:38
In reply to Re: A case of Seroquel induced TD, posted by OldSchool on March 15, 2002, at 10:30:35
Hi OldSchool.
> "Ms. A, a 44-year-old woman with schizophrenia and chronic active psychosis, was resistant to conventional antipsychotic therapy. She was treated for many years with clotiapine, haloperidol, perphenazine, thioridazine, and penfluridol."
It is possible that the true culprit was this person's prior exposure to the older neuroleptics. Although I don't know exactly how it happens, Seroquel (quetiapine) may have "unmasked" the TD that had been both produced *and* masked by the likes of Haldol.
> "As with cases in the literature of clozapine-induced tardive dyskinesia [1], it is possible that the present case of tardive dyskinesia was due to the late effects of previous classical neuroleptic treatment"
I am not touting the safety of using Seroquel or any of the other atypical neuroleptics, but a fuller understanding of the risks these drugs carry of producing TD must take into consideration the treatment history of those people in whom it emerges. Perhaps like Cam W. could provide some insight into the case report. I don't know how to account for the 6 month period of latency between the introduction of Seroquel and the appearance of TD. Perhaps Seroquel is the culprit, but I don't think this case can segregate the contributions of all of the drugs involved. On Medline, you will find anecdotal reports of EPS, including TD, observed in association with all of the atypical neuroleptics. It would be interesting to compare the treatment histories of the individual cases.
Of the atypicals, it is suggested that Clozaril (clozepine) and Seroquel are the least apt to produce EPS. Risperdal seems to be the most apt. In fact, Clozaril and Zyprexa are sometimes used to mitigate pre-existing EPS. It is thought that the ability of these drugs to block serotonin 5-HT2a/c receptors yields a better balance between serotonin and dopamine pathways. Some researchers hypothesize that this balance helps protect one from developing TD. However, Seroquel is the weakest antagonist at these receptors. It is also the weakest dopamine D2 antagonist of all the neuroleptic antipsychotics. Because Haldol and the other older neuroleptics bind so tightly to the D2 receptor, any AP-induced D2 receptor supersensitivity would be masked because most of them remain occupied and blocked by these same drugs. Being the weakest D2 antagonist, and without sufficient 5-HT2a/c receptor antagonism to promote a balance, Seroquel would be the least capable of maintaining the mask, thus allowing EPS to bleed through.
To examine the relative potency of these drugs to bind to various receptors, you can take a look at the following chart. It is an inverse association. The bigger the number, the weaker the attachment.
http://sl.schofield3.home.att.net/medicine/aripiprazole_binding.pdf
- Scott
poster:SLS
thread:97844
URL: http://www.dr-bob.org/babble/20020313/msgs/98200.html