Quality assurance of pharmaceuticals
A compendium of guidelines and related materials Volume 2:
Good manufacturing practices and inspection
WHO good manufacturing practices: specific pharmaceutical products
Sterile pharmaceutical products
Investigational pharmaceutical products for clinical trials in humans
Herbal medicinal products
Herbal medicinal products
The definitions given below apply to the terms used in these
guidelines. They may have different meanings in other
constituents with known therapeutic activity
Substances or groups of substances which are chemically
defined and known to contribute to the therapeutic activity of a
plant material or of a preparation.
herbal medicinal product
product containing, as active ingredients, exclusively plant
material and/or preparations. This term is generally applied to a
finished product. If it refers to an unfinished product, this should
Constituents of a medicinal
plant material which are chemically defined and of interest for
control purposes. Markers are generally employed when constituents
of known therapeutic activity are not found or are uncertain, and
may be used to calculate the quantity of plant material or
preparation in the finished product. When starting materials are
tested, markers in the plant material or preparation must be
A plant (wild or
cultivated) used for medicinal purposes.
medicinal plant material (crude plant material, vegetable
Medicinal plants or parts thereof
collected for medicinal purposes.
powdered plant material, extracts, tinctures, fatty or essential
oils, resins, gums, balsams, expressed juices, etc., prepared from
plant material, and preparations whose production involves a
fractionation, purification or concentration process, but excluding
chemically defined isolated constituents. A plant preparation can be
regarded as the active ingredient whether or not the constituents
having therapeutic activities are known.
Unlike conventional pharmaceutical products, which are usually
prepared from synthetic materials by means of reproducible
manufacturing techniques and procedures, herbal medicinal products
are prepared from material of plant origin which may be subject to
contamination and deterioration, and may vary in composition and
properties. Furthermore, in the manufacture and quality control of
herbal medicinal products, procedures and techniques are often used
which are substantially different from those employed for
conventional pharmaceutical products.
The control of the starting materials, storage and processing
assumes particular importance because of the often complex and
variable nature of many herbal medicinal products and the number and
the small quantity of defined active ingredients present in
Medicinal plant materials should be stored in separate areas. The
storage area should be well ventilated and equipped in such a way as
to protect against the entry of insects or other animals, especially
rodents. Effective measures should be taken to limit the spread of
animals and microorganisms introduced with the plant material and to
prevent cross-contamination. Containers should be located in such a
way as to allow free air circulation.
Special attention should be paid to the cleanliness and good
maintenance of the storage areas, particularly when dust is
The storage of plants, extracts, tinctures and other preparations
require special conditions of humidity and temperature or
protection from light; steps should be taken to ensure that these
conditions are provided and monitored.
To facilitate cleaning and to avoid cross-contamination whenever
dust is generated, special precautions should be taken during the
sampling, weighing, mixing and processing of medicinal plants, e.g.
by the use of dust extraction or dedicated premises.
Specifications for starting materials
In addition to the data called for in sections 14 and 18 of "Good
manufacturing practices for pharmaceutical products"(1), the
specifications for medicinal plant materials should as far as
possible include the following:
• The botanical name, with
reference to the authors.
• Details of the source of the
plant (country or region of origin, and where applicable, method
of cultivation, time of harvesting, collection procedures,
possible pesticides used, etc.).
• Whether the whole plant or
only a part is used.
• When dried plant is purchased,
the drying system.
• A description of the plant
material based on visual and/or microscopical
• Suitable identification tests
including, where appropriate, identification tests for known
active ingredients or markers.
• The assay, where appropriate,
of constituents of known therapeutic activity or
• Suitable methods for the
determination of possible pesticide contamination and the
acceptable limits for such contamination.
• The results of tests for toxic
metals and for likely contaminants, foreign
• The results of tests for
microbial contamination and aflatoxins.
Any treatment used to reduce fungal/microbial contamination or
other infestation should be documented. Instructions on the conduct
of such procedures should be available and should include details of
the process, tests and limits for residues.
Qualitative and quantitative requirements
These should be expressed in the following ways:
1. Medicinal plant material: (a) the quantity of plant material
must be stated; or
(b) the quantity of plant material may be
given as a range, corresponding to
a defined quantity of
constituents of known therapeutic activity.
Name of active ingredient
(a) 900 mg or (b) 830–1000 mg,
corresponding to 25 mg of hydroxyanthracene
calculated as sennoside B
2. Plant preparation:
equivalent quantity or the ratio of plant material to plant
must be stated (this does not apply to fatty or
essential oils); or
(b) the quantity of the plant preparation
may be given as a range, corresponding to a defined quantity of
constituents with known therapeutic activity (see example).
The composition of any solvent or solvent mixture used and the
physical state of the extract must be indicated.
If any other substance is added during the manufacture of the
plant preparation to adjust the level of constituents of known
therapeutic activity, or for any other purpose, the added
substance(s) must be described as "other ingredients" and the
genuine extract as the "active ingredient".
Name of active ingredient
(a) 125 mg ethanolic extract (8:1) or
125 mg ethanolic extract, equivalent to
1000 mg of Sennae folium
or (b) 100–130 mg ethanolic extract (8:1), corresponding
mg of hydroxyanthracene glycosides, calculated as sennoside
Dextrin 20–50 mg
Specifications for the finished product
The control tests for the finished product must be such as to
allow the qualitative and quantitative determination of the active
ingredients. If the therapeutic activity of constituents is known,
this must be specified and determined quantitatively. When this is
not feasible, specifications must be based on the determination of
If either the final product or the preparation contains several
plant materials and a quantitative determination of each active
ingredient is not feasible, the combined content of several active
ingredients may be determined. The need for such a procedure must be
The processing instructions should list the different operations
to be performed on the plant material, such as drying, crushing and
sifting, and also include the temperatures required in the drying
process, and the methods to be used to control fragments or particle
size. Instructions on sieving or other methods of removing foreign
materials should also be given. Details of any process, such as
fumigation, used to reduce microbial contamination, together with
methods of determining the extent of such contamination, should also
For the production of plant preparations, the instructions should
specify any vehicle or solvent that may be used, the times and
temperatures to be observed during extraction, and any concentration
methods that may be required.
5. Quality control
The personnel of quality control units should have particular
expertise in herbal medicinal products to be able to carry out
identification tests, and check for adulteration, the presence of
fungal growth or infestations, lack of uniformity in a consignment
of medicinal plant materials, etc.
Reference samples of plant materials must be available for use in
comparative tests, e.g. visual and microscopic examination and
Sampling must be carried out with special care by personnel with
the necessary expertise since medicinal plant materials are composed
of individual plants or parts of plants and are therefore
heterogeneous to some extent.
Further advice on sampling, visual inspection, analytical
methods, etc., is given in Quality control methods for medicinal
plant materials (2).
6. Stability tests
It will not be sufficient to determine the stability only of the
constituents with known therapeutic activity, since plant materials
or plant preparations in their entirety are regarded as the active
ingredient. It must also be shown, as far as possible, e.g. by
comparisons of chromatograms, that the other substances present are
stable and that their content as a proportion of the whole remains
If a herbal medicinal product contains several plant materials or
preparations of several plant materials, and it is not feasible to
determine the stability of each active ingredient, the stability of
the product should be determined by methods such as chromatography,
widely used assay methods, and physical and sensory or other
1. WHO Expert Committee on Specifications for Pharmaceutical
Preparations. Thirty-second report. Geneva, World Health
Organization, 1992:44–52; 75–76 (WHO Technical Report Series, No.
2. Quality control methods for medicinal plant
materials. Geneva, World Health Organization, 1992
(unpublished document WHO/PHARM/92.559/rev. 1; available on
request from Health Technology and Pharmaceuticals, World Health
Organization, 1211 Geneva 27,
1 Good manufacturing practices for pharmaceutical products, Part Three, section 17. In: WHO Expert Committee on Specifications for Pharmaceutical Preparations. Thirty-second report. Geneva, World Health Organization, 1992:59–72 (WHO Technical Report Series, No. 823). The original numbering has been retained.
2 Parts One and Two, Part Three, section 18, and the Introductory note, General considerations and Glossary of Good manufacturing practices for pharmaceutical products are reproduced elsewhere in this volume (see pp. 6–13, 13–45, 46–53, 75–83).
3 Good manufacturing practices for biological products. In: WHO Expert Committee on Biological Standardization. Forty-second report. Geneva, World Health Organization, 1992, Annex 1 (WHO Technical Report Series, No. 822) and WHO Expert Committee on Specifications for Pharmaceutical Preparations. Thirty-second report. Geneva, World Health Organization, 1993, Annex 3 (WHO Technical Report Series, No. 834).
4 Good manufacturing practices: supplementary guidelines for the manufacture of investigational pharmaceutical products for clinical trials in humans. In: WHO Expert Committee on Specifications for Pharmaceutical Preparations. Thirty-fourth report. Geneva, World Health Organization, 1996, Annex 7 (WHO Technical Report Series, No. 863).
5 Guidelines for the assessment of herbal medicines are provided in Quality assurance of pharmaceuticals: a compendium of guidelines and related materials. Vol. 1. Geneva, World Health Organization, 1997:31–37.
6 Good manufacturing practices: supplementary guidelines for the manufacture of herbal medicinal products. In: WHO Expert Committee on Specifications for Pharmaceutical Preparations. Thirty-fourth report. Geneva, World Heath Organization, 1996, Annex 8 (WHO Technical Report Series, No. 863). p.134-139
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