What is the market for Phase IV pharmaceutical research? Total number
of trials, total number of subjects.

Hi denny!

According to the database at ClinicalTrials.gov, there are currently
115 Phase IV clinical trials underway.  To obtain this information, I
went to:

http://www.clinicaltrials.gov/ct/gui/screen/AdvancedSearch

...and selected "Phase IV" as my search criteria, then selected "Show
all trials, including those no longer recruiting patients."  This
results in a list of all Phase IV trials.  Clicking each link will
take you to a page listing the purpose of the study and the contact
information for the director/sponsor of each study.

Information regarding total number of participants in Phase IV studies
is not available, according to a representative at the Food And Drug
Administration (1-888-INFO-FDA).  She said that the number of study
participants is considered proprietary information by most drug
manufacturers - many will not release this number to the public during
testing.  You may have some luck obtaining the number of participants
in each trial by calling the contact person listed with each trial's
information - however, I called 5 at random and was turned down flatly
by 4 of them.  The fifth gave me a rough number, but informed me that
they had no idea how many would actually be participating until
recruiting ceased.

After Phase IV testing is complete, you can obtain information about
the number of participants in each trial by filing a Freedom Of
Information Act request *for each trial*:

Freedom of Information
http://www.fda.gov/foi/foia2.htm

The FDA representative told me that no information is released without
the specific drug name, and a separate request must be made for
*each*.

Something that might be of further interest is a chart included with
this article about clinical trials, which explaing the various phases
of testing, and gives rough estimates of the number of patients used
in each phase of each trial.

The Drug Development and Approval Process 
http://www.phrma.org/searchcures/newmeds/devapprovprocess.phtml

Hope this helps!

--Missy

Search terms included: [ "phase IV" trials total participants ]

Terrific and fast response! I'm impressed and will return.