Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

14 QUALITY CONTROL OF MEDICINAL AND AROMATIC PLANTS AND THEIR EXTRACTED PRODUCTS
BY HPLC AND HIGH PERFORMANCE THIN LAYER CHROMATOGRAPHY
14.3 Biological and Chemical Standardization
of Drugs
All test procedures ultimately aim to determine the intrinsic potency
of a drug, which is attributable to the chemical constituents present.
Evaluating the biological potency of a drug provides a direct assessment
of its quality. But, the complexity of the procedures and methods forbids
implying this assessment. Moreover, it is not the practical option when one
handles large numbers of samples. The other option, besides biological
testing, is chemical testing, which uses assay procedures to determine the
quantity of chemical compounds, preferably the active ones, to assess the
quality of a product. This is complementary to recording other specifi cations
like macro- and microscopic characteristics.
14.3.1 Chemical Standardization and Markers
Chemical standardization requires fi rst to identify and select a
chemical constituent of a drug and then to elaborate the assay procedure
for quantifi cation of the chosen compound. Selection of the constituent,
called marker, is a diffi cult task based on several considerations: the chemical
profi le of the drug, biological activity of the chemical constituents, successful
development of the assay procedure, ease of procuring or isolating
the marker, and stability of the marker.
The European Union Guidelines defi ne markers as “Chemically
defi ned constituents or groups of constituents of a herbal substance, a
herbal preparation or a herbal medicinal product which are of interest for
control purposes independent of whether they have any therapeutic activity.”
The WHO defi nes markers as “constituents of a medicinal plant material
which are chemically defi ned and of interest for control purposes.”
Markers serve to calculate the quantity of herbal substances or
herbal preparations in the herbal medicinal product if the marker has been
quantitatively determined in the herbal substance or herbal preparations. The
European Medicines Agency differentiates an active marker from an analytical
marker: an active marker contributes to the therapeutic activity of the drug,
whereas an analytical marker serves only the analytical purposes.
The choice of a marker, in first place, should be for a chemical
constituent of the drug responsible for the activity. More than one marker can
be employed for control purposes, separately or in combination. A second
choice of marker is for a defined chemical constituent that is uniquely associated
with the drug. This is true when active constituents of the drug are
not known or active constituents are unobtainable or unstable for assay purposes.
As a last choice, a marker can be selected among more commonly or
ubiquitously present phytoconstituents. In rare cases, a chemical compound
242