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SNRIs | Antidepressant Topic Index | MAOIs

1.  Three Ring Circus

Defined by their three-ring chemical structure, almost all tricyclic antidepressants (TCAs) work in pretty much the same way: norepinephrine reuptake inhibition, alpha-1, H1, and M1 antagonism, and sodium voltage channel blocking. Most also do enough serotonin reuptake inhibition to make a difference, and some are also 5HT2A and 5HT2C antagonists. TCAs discussed on this site include:


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2.  But Wait, There’s Four

Tetracyclic - having four rings - antidepressants like Remeron and amoxapine are usually lumped in with TCAs even they don’t really work enough like TCAs to warrant that. Enough places and papers refer to Remeron (mirtazapine), etc. as TCAs anyway, so we may as well put them on the same page.1 However, Asendin (amoxapine) is unofficially classified as an atypical antipsychotic by Stahl and other pharmacologists, based upon its efficacy in treating schizophrenia and mechanism of action, while all the others have a similar mechanism of action that is completely different than amoxapine, and are grouped as noradrenergic and specific serotonergic antidepressants (NaSSAs). All it takes is one more to be approved in the US and they’re getting their own Crazymeds class.

3.  TCA Dosage Equivalents

As far as tricylic ADs are concerned you’d think it would be fairly easy to put together, as there are three essential components of a TCA’s mechanism of action that make it an effective antidepressant: norepinephrine and serotonin reuptake inhibition, and alpha-1 norepinephrine antagonism. Some of them do more, but those are the main three for AD action. Turns out only three are roughly equivalent as far as raw potency is concerned - desipramine, my dear friend protriptyline, and nortriptyline. So while 25mg of desipramine = 25mg of nortriptyline, and it’s close enough to 1:1 until you hit 100mg, protriptyline’s pharmacokinetics are so loopy that I wouldn’t put any money on one 20mg dose of protriptyline being equivalent to two 10mg doses of protriptyline. Then we start getting into some meds being the active metabolites of others and a hell of a lot of other complexities.

3.1  By the Numbers

Take a look for yourself. These are measures of potency, and potency is not the same as how well a drug works. It isn’t even the same as the effect a drug will have in your brain. Why? These are the base substances, and not the various salts (hydrochloride (HCl), mesylate, pamoate, etc.) that are the active ingredients in many meds. That usually makes a difference in how well a substance is absorbed and distributed throughout your system. According to the results shown on the first table, clomipramine is exactly ten times as potent when it comes to making norepinephrine hang around your synapses than loxapine is, but if the formulations of two drugs resulted in five times as much loxapine per milligram getting to your brain and staying there than was the case with clomipramine, then the clomipramine would be only twice as potent2.

The lower the number, the greater the strength.
SERT: Serotonin transport
NET: Norepinephrine transport
DAT: Dopamine transport
“transport” is another way of referring to reuptake.
These tables are sortable. Just click on a column header to sort the table by that column. Clicking on the same header more than once toggles between ascending and descending.

Binding Profiles of Selected Tricyclic and Tetracyclic Antidepressants

Med (generic)SERTNETDAT5-HT1A5-HT2Aα1α2D2H1Musc
amitriptyline4.30353,25032024268151,2301.0313.8
clomipramine0.28382,1907,00027383,2001903137
desipramine17.60.833,1906,7003151156,3503,40085132
dosulepin8.6465,3102,3002584702,400?3.625
doxepin6829.512,10028326241,1851,3800.2152
imipramine1.40378,5007,650115613,1501,3102468
lofepramine705.418,0004,6002001002,7002,00036067
nortriptyline184.371,14030243582,2651,8858.294
protriptyline19.61.412,1003,800701306,6002,3002525
trimipramine1492,4503,7808,00032246801800.2758
amoxapine5816.04,3102200.6502,600160251,000
loxapine2,4003809,0002,9001.7282,400704.9450
maprotiline5,80011.11,00012,000120909,4003502.0570
mianserin4,0001019,4001904.3744.32,1971.7820
mirtazapine>100,0001,640>100,000?6960819>5,4541.6794

.

From Tricyclic antidepressant pharmacology and therapeutic drug interactions updated Receptor profile, Ki (nmol/l), of TCAs and comparator drugs: uptake inhibition and receptor antagonism (HCR data)


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Mixed with the NSRI reboxetine for comparison.

generic name5-HTNAH1α1Musc5-HT2A
mirtazapine>10,0004,6000.1450067016
mianserin>4,000710.40348207
doxepin6829.50.24248325
amitriptyline20501271829
imipramine76040324680
clomipramine0.145415322535
nortriptyline100106.3553744
dothiepin7870440038260
desipramine180.83110100100280
reboxetine587.2310>1000>1000>1000

.

If you like these kind of data, see the page on SSRI dosage equivalents.

We also have a forum for TCAs on Crazymeds Talk, and Remeron has its own forum, so if this page and the pages for individual TCAs aren’t enough for you, take a look at that part of this site.


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SNRIs | AD Topic Index | MAOIs



1 That the acronym TeCA hasn't caught on doesn't help much either.

2 I made that up just to have an example using TCAs. A real case is Paxil vs. Prozac. Paroxetine is 14 times as potent as fluoxetine in serotonin reuptake inhibition, but Paxil (paroxetine HCl) is only twice as potent as Prozac (fluoxetine HCl).


Tricyclic & Tetracyclic Antidepressants (TCAs) by Jerod Poore is copyright © 2010 Jerod Poore

Last modified on Sunday, 16 March, 2014 at 16:42:59 by JerodPoorePage Author: Jerod PooreDate created: 26 November 2010

All drug names are the trademarks of someone else. Look on the appropriate PI sheets or ask Google who the owners are. The way pharmaceutical companies buy each other and swap products like Monopoly™ real estate, the ownership of any trademarks may have changed without my noticing.





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Almost all of the material on this site is by Jerod Poore and is copyright © 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, and 2014 Jerod Poore. Except, of course, the PI sheets - those are the property of the drug companies who developed the drugs the sheets are about - and any documents that are written by other people which may be posted to this site will remain the property of the original authors. You cannot reproduce this page or any other material on this site outside of the boundaries of fair use copying without the express permission of the copyright holder. That’s usually me, so just ask first. That means if want to print out a few pages to take to your doctor, therapist, counselor, support group, non-understanding family members or something like that - then that’s OK to just do. Go for it! Please. As long as you include this copyright notice and something along the lines of following disclaimer, I’m usually cool with it.



All rights reserved. No warranty is expressed or implied in this information. Consult one or more doctors and/or pharmacists before taking, or changing how you take any neurological and/or psychiatric medication. Your mileage may vary. What happened to us won’t necessarily happen to you. If you still have questions about a medication or condition that were not answered on any of the pages you read, please ask them on Crazy Talk: the Crazymeds Forum.
The information on Crazymeds pertains to and is intended for adults. While some information about children and adolescents is occasionally presented (e.g. US FDA approvals), pediatric-specific data such as dosages, side effects, off-label applications, etc. are rarely included in the articles on drugs or discussed on the forum. If you are looking for information regarding meds for children you’ll have to go somewhere else.
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All information on this site has been obtained through our personal experience and the experiences family, friends, what people have reported on various reputable sites all over teh intergoogles, the medications’ product information / summary of product characteristic (PI/SPC) sheets, and from sources that are referenced throughout the site. As such the information presented here is not intended as a substitute for real medical advice from your real doctor, just a compliment to it. You should never, ever, replace what a real doctor tells you with something from a website on the Internet. The farthest you should ever take it is getting a second opinion from another real doctor. Educate yourself - always read the PI/SPC sheet or patient information leaflet (PIL) that comes with your medications and never ever throw them away.
Crazymeds is not responsible for the content of sites we provide links to. We like them, or they’re paid advertisements, or they’re something else we think you should read to help you make an informed decision about a particular med. Sometimes they’re more than one of those things. But what’s on those sites is their business, not ours.
Very little information about visitors to this site is collected or saved. From time to time I look at search terms used and which pages they bring up in an effort to make the information I present more relevant. And the country of origin, just because I’m geeky like that. That’s about it. Depending on how you feel about Schrodinger, our privacy policy should either assuage or exacerbate your paranoia.
All brand names of the drugs listed in this site are the trademarks of the companies named on the PI/SPC sheet associated with the medication, sometimes on the pages about the drugs, even though those companies may have been acquired by other companies who may or may not be listed in this site by the time you read this. Or the rights to the drug were sold to another company. And any or all of the companies involved may have changed their names.
Crazymeds is optimized for the browser you’re not using on the platform you wish you had. Between you and me, it all looks a lot cleaner using Safari or Chrome, although more than half of the visitors to this site use either Safari or Internet Explorer, so I’m doing my best to make things look nice for IE as well. I’m using Firefox and running Windows 72. On a computer that sits on top of my desk. With a 23 inch monitor. Hey, at least you can make the text larger or smaller by clicking on the + or - buttons in the upper right hand corner. If you have Java enabled. Like 99% of the websites on the planet, Crazymeds is hosted on domain running an open source operating system with a variety of open source applications, including the software used to display what you’ve been reading. As such Crazymeds is not responsible for whatever weird shit your browser does or does not do when you read this site3.
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1 While there are plenty of books to help you with hypochondria, for some reason there’s not much in the way of websites. Then again, staying off of the Internet is a large part of curing/managing the disorder.

2 Remember kids, Microsloth operating systems are like TOS Star Trek movies with in that every other one sucks way, way more. With TOS Star Trek movies you don’t want to bother watching the odd-numbered ones. With Microsloth OS you don’t want to buy and install the even-numbered ones. Anyone who remembers ME and Vista knows what I mean.

3 Have I mentioned how open source operating systems for commercial applications is one of the dumbest ideas in the history of dumb ideas?
[begin rant] I rent a dedicated server for Crazymeds. It’s sitting on a rack somewhere in Southern California along with a bunch of other servers that other people have rented. The hardware is identical, but no two machines have exactly the same operating systems. I don’t even need to see what is on any of the others to know this. If somebody got their server at the exact same time, with the exact same features as I did, I’m confident that there would be noticeable differences in some aspects of the operating systems. So what does this mean? For one thing it means that no two computers in the same office of a single company have the same operating system, and the techs can spend hours figuring out what the fuck the problem could be based on that alone. It also means that application software like IP board that runs the forum here has to have so many fucking user-configurable bells and whistles that even when I read the manual I can’t find every setting, or every location that every flag needs to be set in order for a feature to run the way I want it to run. And in the real world it means you can get an MBA not only with an emphasis on resource planning, but with an emphasis on using SAP - a piece of software so complex there are now college programs on how to use it. You might think, “But don’t people learn how to use Photoshop or Adobe Illustrator in college?” Sure, in order to create stuff. And in a way you’re creating stuff with SAP. But do you get a Bachelor of Fine Arts degree with an emphasis on Photoshop?
Back in the Big Iron Age the operating systems were proprietary, and every computer that took up an entire room with a raised floor and HVAC system, and had less storage and processing power than an iPhone, had the same operating system as every other one, give or take a release level. But when a company bought application software like SAP, they also got the source code, which was usually documented and written in a way to make it easy to modify the hell out of it. Why? Because accounting principles may be the same the world over, and tax laws the same across each country and state, but no two companies have the same format for their reports, invoices, purchase orders and so forth. Standards existed and were universally ignored. If something went wrong it went wrong the same way for everyone, and was easy to track down. People didn’t need to take a college course to learn how to use a piece of software.
I’m not against the open source concept entirely. Back then all the programmers read the same magazines, so we all had the same homebrew utilities. We even had a forerunner of QR Code to scan the longer source code. Software vendors and computer manufacturers sponsored conventions so we could, among other things, swap recipes for such add-ons and utilities. While those things would make our lives easier, they had nothing to do with critical functions of the operating system. Unless badly implemented they would rarely cause key application software to crash and burn. Whereas today, with open source everything, who the hell knows what could be responsible some part of a system failing. [/end rant]

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