Design Space...a
simple explanation...
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Design Space- What is the basic
explanation for the ICH Q8 “Design Space” concept?
Design Space is
“the multi-dimensional combination and interaction of input variables (e.g.
material variables) and process parameters that have been demonstrated to
provide
assurance of quality.
What’s all that supposed to
mean?
Maybe a basic example might help…along with the typical diagram
which represents various
bodies of knowledge regarding our process...I
bet this diagram gets as overworked as the "V
Model"...but I
digress...
(I realize it looks clunky, but the rectangles work with the
html code...)
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Industry
Survey...
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So let’s assume the unit
operation is mixing a powder in water…and let’s only look at one
variable….for example, the temperature of the water used in mixing
process- obviously this is
a gross simplification but it really is just
to discuss the concept…and the diagram above would
indicate 2
variables, say a range of temperature and pH for each state of
control…
Area of
knowledge-The process has been tested, with
documented results, within your “area
of knowledge”…your broad range of
knowldege may include some situations that did not result
in
success...you're just documenting what you know through testing and
experiment...
Obviously it is implied that testing outside these stated
boundaries have never been formally
tested and documented…seems
reasonable…who’s trying to mix powders with water near
freezing, for
example…
Area of
success- The process has been tested, and
consistently produces desired results
within your “area of
success”…note the increasing control of variable i. e. temperature...
establishing these more realistic parameters begins to define the range you
absolutely need
to operate your process
within...
Area of
control- Your “area of control” defines
boundaries for selected parameters that will
obviously produce desired
results…this represents the most restrictive area for accepting
variations in process parameters. This is what gets documented as
development data and
you will be held to it, so get it right…as the
expression goes, “Quality by Design…”
Expanding this approach to cover an
entire process of multiple unit operations with multiple
variables is
obviously much more complicated than the simplistic example cited
above…especially for you biotech types…but you might get a basic feel based
on this simple
example…
What is the benefit of all of
this?
You own your information…you establish your parameters and
performance
criteria…understand this…why are you killing yourself to
maintain control within a narrow band
if it doesn’t have any impact on
product quality…thoughtful review and analysis of these issues
will
allow for careful control of critical parameters and less precise control where
it would be
appropriate…
Area of
Knowledge
(20 +/- 6 Deg C)
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Area of
Success
(20 +/- 3 Deg C)
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Area of
Control
(20 +/- .5 Deg C)
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Area outside of
applicable
testing
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The "Design Space"
Diagram...
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