Prodrug
A prodrug is a medication or compound that, after
administration, is metabolized (i.e., converted within the body) into a pharmacologically
active drug. Inactive prodrugs are pharmacologically inactive medications that
are metabolized into an active form within the body. Instead of administering a
drug directly, a prodrug might be used instead to improve how a medicine is
absorbed, distributed, metabolized, and excreted (ADME). Prodrugs are often
designed to improve bioavailability when a drug itself is poorly absorbed from
the gastrointestinal tract. A prodrug may be used to improve how selectively
the drug interacts with cells or processes that are not its intended target.
This reduces adverse or unintended effects of a drug, especially important in
treatments like chemotherapy, which can have severe unintended and undesirable
side effects.
Advantages of Prodrugs:
1.
More stable
2.
Better bioavailability
3.
Low side effects
4.
Less toxic
5.
Desirable
pharmacokinetic profile.
6.
Increase concentration
of drug at site of action.
7.
Increase duration of
action of drug
Prodrugs can be classified into two major types, based
on how the body converts the prodrug into the final active drug form:
Type I prodrugs are bioactivated inside the cells
(intracellularly). Examples of these are anti-viral nucleoside analogs that
must be phosphorylated and the lipid-lowering statins.
Type II prodrugs are bioactivated outside cells
(extracellularly), especially in digestive fluids or in the body's circulatory
system, particularly in the blood. Examples of Type II prodrugs are salicin and certain antibody-, gene- or virus-directed enzyme
prodrugs used in chemotherapy or immunotherapy.
Both major types can be further categorized into subtypes,
based on factors such as (Type I) whether the intracellular bioactivation
location is also the site of therapeutic action, or (Type 2) whether or not
bioactivation occurs in the gastrointestinal fluids or in the circulation
system.
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