Microorganisms form a major part of the natural recycling processes for biological matter in the environment. As such, they possess a wide variety of degradative capabilities, which they are able to exert under relatively mild physicochemical conditions.
SPOILAGE—CHEMICAL AND PHYSICOCHEMICAL
DETERIORATION OF PHARMACEUTICALS
Microorganisms form a major part of the natural recycling processes for
biological matter in the environment. As such, they possess a wide variety of
degradative capabilities, which they are able to exert under relatively mild
physicochemical conditions. Mixed natural communities are often far more
effective cooperative bio-deteriogens than the individual species alone, and
sequences of attack of complex substrates occur where initial attack by one
group of microorganisms renders them susceptible to further deterioration by
secondary, and subsequent, microorganisms. Under suitable environmental
selection pressures, novel degradative pathways may emerge with the capability
to attack newly introduced synthetic chemicals (xenobiotics). However, the
rates of degradation of materials released into the environment can vary greatly,
from half-lives of hours (phenol) to months (‘hard’ detergents) to years
(halogenated pesticides).
The overall rate of deterioration of a chemical depends on its molecular
structure; the physicochemical properties of a particular environment; the type
and quantity of microbes present; and whether the metabolites produced can
serve as sources of usable energy and precursors for the biosynthesis of
cellular components, and hence the creation of more microorganisms.
Pharmaceutical formulations may be considered as specialized
microenvironments and their susceptibility to microbial attack can be assessed
using conventional ecological criteria. Some naturally occurring ingredients
are particularly sensitive to attack, and a number of synthetic components, such
as modern surfactants, have been deliberately constructed to be readily
degraded after disposal into the environment. Crude vegetable and animal drug
extracts often contain a wide assortment of microbial nutrients besides the
therapeutic agents. This, combined with frequently conducive and unstable
physicochemical characteristics, leaves many formulations with a high potential
for microbial attack unless steps are taken to minimize it.
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