It also might be the case that the metabolite, in this case desipramine,
is the primary substance which is active.  The substance you ingest is
slightly different.  The important thing about the difference might be
that some other company could get a patent on trimipramine and could
profit from it.

I do not know whether trimipramine is active, or which metabolites may or
may not be active.  However, it is very true that many drug companies
tried to get on the bandwagon after the huge success of the first
tricyclic, imiprimane.  As many as 10 different tricyclics were marketed,
with relatively minor changes to the imipramine molecule.  The changes
were motivated mainly by the need to create a different substance to
obtain a new patent on.  There were minor differences between all the
brands of tricyclics, but essentially all were the same.  

The term "me-too" was coined to describe this type of drug development.
The practice still persists today.  A notable example would be the statin
drugs used to lower cholesterol.  Many minor variations on the same basic
drug are marketed under various competing brand names.

Here is an informative article I located on the internet which
addresses metabolization.  This specific article refers to the
metabolization of Tricyclic Anti-depressants.

<begin>
It is perhaps not cultural as much as the compound clomipramine was
first used
and tested in Europe before it's introduction to the U.S.. So it would
stand to
reason that the European archives would have a larger body of research
and
study of this med. The actual motivation for mythelating hydrogenating
and
chlorinating parent compounds is originally not done for a better drug
but to
re-patent and trademark an older one-greed actually! But in doing the
chemical
manipulation it is determined that some meds do indeed have certain
properties
that the parent compound doesn't.

The impetus in developing many variations of tca's was also to try
and find a version of an established med that didn't take 8 weeks to
alleviate a depression-so the drug companies tried to create a more
metabolically accesible product that reduced the bodies need to
metabolize it
to a further useable state. Sort of like the differences between
mincycline and
doxycycline versions of tetracycline-they have the basicaly same range
of
antimicrobial activity and acheive their destruction of bacteria the
same but
are metabolized differently and have different plasma and tissue
levels. After
they were used in the field it was discovered that minocycline is more
useful
for prostatic infections then doxy as it has a certain affinity to
penetrate
the gland better and maintains higher concentrations longer. Also it
may be
more useful for arthritic conditions for unknown reasons perhaps the
same
reasons.

By tinkering with established compounds it is cheaper then creating
new ones. As for clomipramine being more like an ssri-its sort of a
reaching
for comparisons. The goal of most med companies is to try and create
products
that mimic the viability of maoi meds without the side effects-this
prompted
the vast surge of research in this field in the early seventies with
the range
of tca's and their analogues. Years ago we considered the tca's either
adrenegic or serotinergic meaning sedating or innervating regardless
of their
actual amine activity which hits many sites including epinephrine-nor
epinephrine-serotonin-and many other metabolites of these amines in
different
ways depending upon the way the drug was tinkered with. By including a
chlorine
ion or hydrogen ion in the molecular chain the organic structure has a
different affinity at the cellular level to bind or not bind with
certain
amines at one or another site along the amine chain or the receptor
chain. This
is why one may find one variant of a compound more succesful then
another-perhaps just due to ones current biology which changes
constantly-then
explaining why the drug poops out so to speak. If the affinity to a
certain
process is weaker in one drug than another this happens as well.

 So it may be hypothisized that for you anafranil had a weaker
imipramine affect then imipramine itself due to the inclusion of the
chloride ion. But ultimately it is the actual effect of imipramine
itself that does the work. Imipramine has been studied the most in the
U.S. simply because it was the first tricyclic discovered and
extensively used - so it became the standard and reference point.
Amazing as it was initially discovered as a treatment for the common
cold. I prefer the pamoate salt version vrs the hydrochloride salt
version as I have seen the pamoate have a gentler and more effective
result-again probably due to the bodies ability to absorb the pamoate
faster and more completely then the hydrochloride-but I have also seen
the opposite as well.
<end