Formulation
Clinically useful drugs are formulated by drug
companies into preparations that can be administered
orally. intra\"enously. or by another route. The fonnu·
lation of a drug depends on the following factors:
-The barriers that the drug is capable of passing.
Intravenous drugs are injected directly into the blood
stream. In contrast, oTal preparations must pass
through the wall of the gastrointestinal tract and
blood vessel walls before entering the bloodstream.
-The setting in which the drug will be used. An
intravenous preparation might be appropriate for a
drug which is administered during surgery, but
would be inappropriate for home administration of
aspirin
.
-The urgency of the medical situation
. The delaybefore onset of action varies between preparations of
the same drug. Emergency situations often caU for
intravenous administration of agents which might
normaUy be administered by another route.
-Stability of the drug. Drugs which are denatured by
acid are not good candidates for oral preparations
because they may be destroyed in the stomach
(stomach pH = 2).
• First Pass Effect.
Blood from the gastrointestinal tract passes
through the liver before entering any other
organs. During this first pass through the liver, a
fraction of the drug (in some cases nearly all) can be
metabolized to an inactive or less active derivative.
The inactivation of some drugs is so great that the
agents are useless when administered orally.
