![[dr. bob]](/dr-bob-sm.gif)
Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 17 of 17. This is the beginning of the thread.
Posted by Janelle on March 30, 2002, at 2:15:32
I've read that certain foods (I don't recall which ones - cheese?) must NOT be eaten if a person is on an MAOI, and I'm wondering why not?
Is it that the inhibition of the enzyme (monamine oxidase?) also inhibits metabolism of certain foods?
Thanks!
Posted by fachad on March 30, 2002, at 6:18:20
In reply to Why R there diet restrictions w/ MAOI's?, posted by Janelle on March 30, 2002, at 2:15:32
MAO, like most things in the body, does more than one thing. It breaks down monoamines like NE, 5HT, and dopamine.
It also breaks down a protein amino acid called "tyramine". Tyramine has the effect of increasing blood pressure.
So if you are on an MAOI and you eat tyramine containing foods, your blood pressure can shoot up to extremely dangerous levels. This potentially fatal reaction is called a "hypertensive crisis" and requires immediate medical attention.
The possibility of a patient having a hypertensive crisis has made many pdocs steer away from prescribing MAOIs.
> I've read that certain foods (I don't recall which ones - cheese?) must NOT be eaten if a person is on an MAOI, and I'm wondering why not?
>
> Is it that the inhibition of the enzyme (monamine oxidase?) also inhibits metabolism of certain foods?
> Thanks!
Posted by Janelle on March 30, 2002, at 15:26:35
In reply to Re: Why R there diet restrictions w/ MAOI's? » Janelle, posted by fachad on March 30, 2002, at 6:18:20
Fachad,
First, thanks for the explanation about MAOI's and diet restrictions. My understanding now is that if a person is on an MAOI, which inhibits MAO from breaking down tyramine, and a person eats tyramine containing food, the tyramine which would then be *free* so to speak would shoot the person's BP through the roof.
What about a person with chronic LOW BP? This question literally just occurred to me as I'm typing this! Let's say I was on an MAOI and ate food that contained tyramine, with my low BP, would it still be raised so (too) high, or might it just reach a normal level?!!! Hmmm ... ironically, whenever I go to a doc and they take my BP they tell me I'm "lucky" to have low BP - everyone is so concerned about high BP, but lemme tell you, low BP is the pits. It makes you tired and lethargic, you get dizzy if you stand up too fast, and a host of other bothersome symptoms. Not that I want high BP, I just want NORMAL BP, like I used to have.
I've asked various docs what can be done about low BP and they kinda shrug and avoid the question. A few have told me to increase my salt intake. So it's my understanding that there's virtually nothing to do for low BP.
I have no intention of going on an MAOI, but can't help wondering if it could take care of my low BP if I did take one and ate tyramine-containing foods! Just a stupid thought ...!
Posted by Janelle on March 30, 2002, at 15:31:18
In reply to Re: Why R there diet restrictions w/ MAOI's? » Janelle, posted by fachad on March 30, 2002, at 6:18:20
Fachad,
I have a parallel question to one I had about SSRI's (can't remember if you were one of the people who had answered that question or not) ... why, if MAOI's are designed to inhibit MAO, are there a bunch of different brands of them - is the chemical structure of each MAOI different so each MAOI acts on several different things (besides MAO) and these things vary from MAOI to MAOI ... like the way I was told that each SSRI affects several different things, and these things vary from SSRI to SSRI (they all do not just affect Serotonin), and this is why different people react differently to the various SSRI's. Is it like this for MAOI's also?
Posted by christophrejmc on March 31, 2002, at 1:02:03
In reply to FACHAD: follow-up question #2 re MAOI's! » fachad, posted by Janelle on March 30, 2002, at 15:31:18
(Hope you don't mind me answering your question directed to fachad...)
> why, if MAOI's are designed to inhibit MAO, are there a bunch of different brands of them - is the chemical structure of each MAOI different so each MAOI acts on several different things (besides MAO) and these things vary from MAOI to MAOI ... like the way I was told that each SSRI affects several different things, and these things vary from SSRI to SSRI (they all do not just affect Serotonin), and this is why different people react differently to the various SSRI's. Is it like this for MAOI's also?
There are two major differences in the MAOIs: selectivity and reversability.
There are two subtypes of MAO, A and B; some MAOIs selectively inhibit only one isozyme, the others inhibit both (although not always equally).
Reversability pertains to how an MAOI binds to MAO. Once an irreversable MAOI binds to MAO, it cannot be detached. The reversable inhibitors (all of which selectively deanimate MAO-A (the subtype responsible for most of the destruction of tyramine)) only bind to MAO for a short while and can be displaced by certain biogenic amines (most importantly tyramine), thus there is a very low risk of tyramine-induced hypertensive crisis.
There are also differences within each group unrelated to MAO inhibition (like the SSRIs).
Also, in reference to your first question: I don't think your initial BP would really matter. (MAOIs actually decrease BP for most people, by the way.) Your BP might not increase as much as someone normo-/hypertensive, but I believe it would still be at an uncomfortable level. If you think that you have Neurally Mediated Hypotension, there are medications used to treat it...
Hope this is of some help.
-Christophre
Posted by fachad on March 31, 2002, at 20:52:47
In reply to FACHAD: follow-up question #1 re MAOI's! » fachad, posted by Janelle on March 30, 2002, at 15:26:35
Well, your question shows that you do understand the mechanics of the MAO / tyramine / BP issue.
But MAOIs for a person with low BP is just a terrible idea. First, MAOIs cause low BP; it is one of the most common side effects.
Second, to eat even a little tyramine food to try to raise your BP could be disastrous. You would most likely dramatically overshoot and end up with dangerously high BP.
They don't call it a "hypertensive crisis" for nothing. It happens very fast and puts people at risk for stroke or other serious problems.
For your chronic low BP, I find that caffene or Sudafed (psueduoephedrine, a decongestant) raise my BP slightly. Both increase BP by causing blood vessels to constrict.
> Fachad,
>
> First, thanks for the explanation about MAOI's and diet restrictions. My understanding now is that if a person is on an MAOI, which inhibits MAO from breaking down tyramine, and a person eats tyramine containing food, the tyramine which would then be *free* so to speak would shoot the person's BP through the roof.
>
> What about a person with chronic LOW BP? This question literally just occurred to me as I'm typing this! Let's say I was on an MAOI and ate food that contained tyramine, with my low BP, would it still be raised so (too) high, or might it just reach a normal level?!!! Hmmm ... ironically, whenever I go to a doc and they take my BP they tell me I'm "lucky" to have low BP - everyone is so concerned about high BP, but lemme tell you, low BP is the pits. It makes you tired and lethargic, you get dizzy if you stand up too fast, and a host of other bothersome symptoms. Not that I want high BP, I just want NORMAL BP, like I used to have.
>
> I've asked various docs what can be done about low BP and they kinda shrug and avoid the question. A few have told me to increase my salt intake. So it's my understanding that there's virtually nothing to do for low BP.
>
> I have no intention of going on an MAOI, but can't help wondering if it could take care of my low BP if I did take one and ate tyramine-containing foods! Just a stupid thought ...!
Posted by fachad on March 31, 2002, at 21:00:52
In reply to FACHAD: follow-up question #2 re MAOI's! » fachad, posted by Janelle on March 30, 2002, at 15:31:18
Once again, it boils down to "intersubjective differences".
People just have these unique biochemistries that react differently to different drugs, even though those drugs are supposed to do the same thing.
I think part of it is also subjective perception and subjective interpretation. By that I mean there is what the drug does (in your brain), and how you experience it and interpret it (in your mind).
> Fachad,
>
> I have a parallel question to one I had about SSRI's (can't remember if you were one of the people who had answered that question or not) ... why, if MAOI's are designed to inhibit MAO, are there a bunch of different brands of them - is the chemical structure of each MAOI different so each MAOI acts on several different things (besides MAO) and these things vary from MAOI to MAOI ... like the way I was told that each SSRI affects several different things, and these things vary from SSRI to SSRI (they all do not just affect Serotonin), and this is why different people react differently to the various SSRI's. Is it like this for MAOI's also?
Posted by Janelle on April 1, 2002, at 0:46:41
In reply to Re: FACHAD: follow-up question #2 re MAOI's! » Janelle, posted by christophrejmc on March 31, 2002, at 1:02:03
Hi there,
I don't mind at all that you answered my question directed to fachad, in fact, I apprecite the extra info!
I'm just not sure I follow it all ...
The irreversable MAOI sounds horrible - why would there be an irreversable med? I think I must be missing something! You wrote "once an irreversable MAOI binds to MAO, it cannot be detached." EEEK - this sounds very scary. If the MAOI can't be detached from the MAO, why would a person keep needing to take that MAOI day after day?
Posted by christophrejmc on April 2, 2002, at 0:23:00
In reply to CHRISTOPH: More about MAOI's! » christophrejmc, posted by Janelle on April 1, 2002, at 0:46:41
> The irreversable MAOI sounds horrible - why would there be an irreversable med? I think I must be missing something! You wrote "once an irreversable MAOI binds to MAO, it cannot be detached." EEEK - this sounds very scary. If the MAOI can't be detached from the MAO, why would a person keep needing to take that MAOI day after day?
Well, irreversable just means that once you stop the MAOI, MAO levels won't return to normal until they are re-synthesized (usually within a week or two depending on age, gender, &c.).
Posted by djmmm on April 2, 2002, at 10:21:43
In reply to CHRISTOPH: More about MAOI's! » christophrejmc, posted by Janelle on April 1, 2002, at 0:46:41
"irreversible" just refers to the chemical bond the MAOI forms to the enzyme...
Posted by BlueJay Bird on April 2, 2002, at 14:33:17
In reply to Re: CHRISTOPH: More about MAOI's!, posted by djmmm on April 2, 2002, at 10:21:43
Posted by BlueJay Bird on April 2, 2002, at 14:34:22
In reply to THANK YOU BOTH! :-) (nm), posted by BlueJay Bird on April 2, 2002, at 14:33:17
Posted by christophrejmc on April 2, 2002, at 18:20:26
In reply to Re: CHRISTOPH: More about MAOI's!, posted by djmmm on April 2, 2002, at 10:21:43
> "irreversible" just refers to the chemical bond the MAOI forms to the enzyme...
True, but what about Parnate (and others that aren't truly irreversible in that sense) being classified as irreversible? Also, it's my understanding that not a whole lot is known about the exact mechanism of MAO inhibition... am I wrong?
Posted by djmmm on April 3, 2002, at 7:04:13
In reply to Re: CHRISTOPH: More about MAOI's! » djmmm, posted by christophrejmc on April 2, 2002, at 18:20:26
As far as I know Parnate is also an irreversible MAOI. It too forms an "irreversible" chemical bond (covalent) to the MAO enzyme...Parnate has a rather short half life, but active metabolites, and these active metabolites also bond to MAO.
Posted by Elizabeth on April 4, 2002, at 22:08:53
In reply to Re: CHRISTOPH: More about MAOI's!, posted by djmmm on April 3, 2002, at 7:04:13
> As far as I know Parnate is also an irreversible MAOI.
Yeah, that's my understanding too. Irreversible enzyme inhibition just means that the drug interacts with the enzyme (here, MAO) in such a way that the enzyme is effectively "destroyed," as opposed to competitive or reversible inhibitors, which tack onto the enzyme but can be displaced by other substrates if high enough concentrations (of the other substrate, that is) are present. I'm not very up on biochemistry, but I believe that the "bond" formed isn't an ordinary covalent bond -- enzymes like MAO are big, complicated molecules that interact in big, complicated ways. (Nardil and Parnate themselves are pretty simple though -- both of them are very similar to amphetamine.)
Irreversible enzyme inhibitors are also sometimes called "suicide inhibitors," which is either very appropriate or in very poor taste (I can't decide which) when applied to an antidepressant.
> Parnate has a rather short half life, but active metabolites, and these active metabolites also bond to MAO.
That's interesting. I didn't know that anything was known about the metabolites of Parnate, except that they aren't amphetamine or methamphetamine.
-elizabeth
Posted by djmmm on April 5, 2002, at 12:50:46
In reply to Re: More about MAOI's! » djmmm, posted by Elizabeth on April 4, 2002, at 22:08:53
The irreversible bond is a covalent bond...you are correct in saying that the reversible MAOIs are displaced, in fact, it is tyramine that displaces the reversible MAOI bond at higher concentrations.
Posted by Elizabeth on April 7, 2002, at 19:56:16
In reply to Re: More about MAOI's!, posted by djmmm on April 5, 2002, at 12:50:46
> The irreversible bond is a covalent bond...
Ahh okay. (Well, we knew it wouldn't be ionic...) Like I said, I don't know much biochemistry; enzymes seem large and mysterious to me!
> you are correct in saying that the reversible MAOIs are displaced, in fact, it is tyramine that displaces the reversible MAOI bond at higher concentrations.
Tyramine, or any other substrate at high enough concentrations!
-e
This is the end of the thread.
Psycho-Babble Medication | Extras | FAQ
Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.org
Script revised: February 4, 2008
URL: http://www.dr-bob.org/cgi-bin/pb/mget.pl
Copyright 2006-17 Robert Hsiung.
Owned and operated by Dr. Bob LLC and not the University of Chicago.