World Health Organization. Quality Control Methods For Medicinal Plant Materials

Geneva, World Health Organization, 1998. — 127 p.Plant materials are used throughout developed and developing countries as home remedies, over-the-counter drug products and raw materials for the pharmaceutical industry, and represent a substantial proportion of the global drug market. It is therefore essential to establish internationally recognized guidelines for assessing their quality. The World Health Assembly - in resolutions WHA31.33 (1978), WHA40.33 (1987) and WHA42.43 (1989) - has emphasized the need to ensure the quality of medicinal plant products by using modern control techniques and applying suitable standards. This manual describes a series of tests for assessing the quality of medicinal plant materials.
The tests are designed primarily for use in national drug quality control laboratories in developing countries, and complement those described in The international pharmacopoeia,' which provides quality specifications only for the few plant materials that are included in the WHO Model List of Essential Drugs.'
This manual does not constitute a herbal pharmacopoeia, but a collection of test procedures to support the development of national standards based on local market conditions, with due regard to existing national legislation and national and regional norms. Publications containing relevant specifications and standards, including those related to the food industry, are listed in the References and Bibliography.
The test methods described here are the best methods currently available. The manual will be revised as needed to incorporate improvements and additional tests and to reflect developments in work being carried out at national and regional levels, including projects aimed at finding replacements for toxic reagents.
In addition to the test methods, some suggestions regarding general limits for contaminants are included. They should be considered as a basis for establishing national limits. WHO is not currently able to recommend limits for contaminants since these are too diverse and there is a lack of consensus. For instance, the draft proposal for limits for some pesticides published in Pharmeuropa, 1993, 5(1): 19, is far more restrictive than that proposed here.
The test procedures cannot take account of all possible impurities. Common sense and good pharmaceutical practice should be applied in deciding whether an unusual substance not detectable by the prescribed tests can be tolerated.
The analysis of medicinal plant materials is not restricted to those methods discussed or recommended here and many techniques similar to those used for the analysis of synthetic drugs are also frequently employed (e.g. volumetric analysis, gravimetric determinations, gas chromatography, column chromatography, high-performance liquid chromatography and spectrophotometric methods). Details of all these methods can be found in The international pharmacopoeia.