What Does "In Vitro" and "In Vivo" Mean?

QUESTION: I have been reading more and more medical material, to better
understand my own health status. I keep coming across reports of a medicine's
effectiveness "in Vitro" and "in Vivo". I think I understand what it means,
but will you explain this concept?
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ANSWER: I am sure you have already consulted your medical dictionary (and
I'll bet you have one), but for everyone's benefit, a few definitions first.
Both terms are derived from the Latin, "vitro" referring to glass, and "vivo"
to life. When a medication is effective in vitro it means it has been shown
to have an action in an artificial or "glass" environment, a test tube being
the example, representing laboratory investigation. Usually this occurs in
the first stages of developing a new medication, when testing reveals that a
possible benefit can be achieved. These laboratory experiments give
scientists the first lead towards a new discovery or breakthrough. Yet that's
a long way from providing a usable ingredient for medication, for there are
still safety tests needed to prove that there are no harmful effects
associated with the new chemical or agent. This experimentation must first be
conducted in animals, and then human volunteers, in living subjects or "in
vivo". When safety has been demonstrated, testing in actual patients may then
be started, and the long process of proving that the good or beneficial
outcomes seen in the first stages of investigation actually occur in real,
live patients. Many times the hopes influenced by the initial results can not
be demonstrated in actual situations, and the research must be abandoned.
Developing safe and effective medicines is a long and costly process which
explains, in part, why medications are sometimes so expensive.