Read this article to learn about the Standardisation of Herbal Medicines. After reading this article you will learn about: 1. General Considerations of Standardisation of Herbal Medicines 2. Procedures and Analytical Methods Used for Achieving “Standard” Herbal Medicines.
General Considerations of Standardisation of Herbal Medicines:
Apart from the enormous analytical and technical problems in standardisation of herbal medicines, standards for ingredients and recommended daily doses (RDDs) have not been clearly established by any of the regulatory authorities in the world.
In some Asian countries where herbal medicines are widely used (e.g. China, India, Thailand), and in some European countries (e.g. Germany), monographs of the more commonly used herbal products have appeared in national pharmacopoeias and similar botanical data bases.
These monographs can be a source of information to estimate RDDs. Furthermore, a text book by Fetrow and Avila (2001) provides a benchmark for ingredients and dosage levels for a large number of plants used in complementary and alternative medicines.
At the international level, the World Health Organization (WHO) (World Health Organization, 2004) has developed a strategy to review traditional medicines and included within this review is a program to develop monographs for herbal ingredients.
In European countries, the European Scientific Cooperative on Phyto-therapy (ESCOP) was established to advance the scientific status of phytomedicine and to assist with the harmonisation of their regulatory status.
Additionally, the Association of South East Asian Nations (ASEAN) has established a committee to assure the quality of herbal medicines, particularly those most widely and commonly used by the people in the ASEAN countries, as well as to promote their utilisation in primary health care.
A Pharmacopoeia is a collection of quality standards for medicines and their components. In order to obtain marketing authorization for a medical product, the ingredients or the medicinal product must generally comply with a pharrpacopoeial standard. Thus, pharmacopoeial standards may provide guidance on acceptable purity criteria for that ingredient.
An important aspect of the quality control of herbal extracts is the need to use consistent quality herbal extracts. Standardised extracts arise out of the need to create a uniform product, with batch-to-batch consistency. An herbal extract should be standardised for content of the active constituents to the limits that are set in its monograph.
The extract, for which the active constituents (single or groups) are known, can be standardised so that it contains a known amount of the active ingredients in a clearly defined amount of an herbal extract. For example, pomegranate fruit peel extract, which is used in antioxidant preparations, should be standardised to contain allergic acid content not less than 13% w/w.
Similarly, Senna alata leaf extract that is used in antifungal preparations should be standardised to contain total anthraquinone content not less than 16% w/w. However, where possible, it is better to define a ‘fingerprint’ of the herbal extract.
There are two types of standardizations. One is based on identifying and quantifying an extract to a pure compound e.g. curcumin, capsaicin, allicin, etc. The second identifies and concentrates one or more as active constituents, making it as a concentrated active constituent extract.
This means that other naturally occurring constituents in the extract are displaced. The examples of the latter are rhinacanthin-rich Rhinacanthus nasutus extract, madecassoside and asiaticoside-rich Centella asiatica extract, and anthraquinone- rich Senna alata extract.
By definition, a standardised herbal extract involves pre-determining one or a number of biochemical constituents as either active, or as marker, compounds, and this result in three very distinct types of herbal extracts.
1. The Active Constituent Extracts:
The active constituent extracts may be only a partial representation of the herb’s normally occurring constituents. This limits the broad range of known traditionally properties and uses of the herb in favour of a single use. For example, curcumin, capsaicin, asiaticoside, etc.
2. The Active Constituent-Enriched Extracts:
The high degree of concentration necessary to produce this type of extract causes a corresponding displacement and lack of other constituents, which in a few cases have subsequently been shown to be even more effective than the originally presumed active constituent.
For example, the antifungal activity of rhinacanthin-rich Rhinacanthus nasutus extract against Trichrophyton rubrum (MIC 7.5 µg/ml) is higher than that of its main active constituent, rhinacanthin-C (MIC 15.1 µg/ ml).
The antifungal activity of anthraquinone (aloe-emodin and emodin) rich Senna alata extract against T. mentagrophytes and Microsporum gyseum (MICs 62 and 250 µg/ml, respectively) is higher than that of its main active constituents, aloe-emodin (inactive) and emodin (MICs 125 and 1000 µg/ml, respectively.
3. Marker Extract:
This type of the extracts establishes that a specified amount of a marker compound is present in the extract. It must be noted that a marker does not represent the active constituent, but is selected as a biochemical constituent characteristic of the plant.
The marker extracts are used for positive identification, or to create a higher degree of uniform potency, but not proven as active constituents. For the latter, it remains to be proven whether this is consistent with the potency of the whole herb.
Procedures and Analytical Methods Used for Achieving “Standard” Herbal Medicines:
Currently, quality-related problems (lack of consistency, safety, and efficacy) seem to be overshadowing the potential genuine health benefits of various herbal preparations. A major cause of these problems seems to be related to the lack of simple and reliable analytical methods for the chemical analysis of herbal materials.
The active constituent is responsible for the intended pharmacological activity or therapeutic effects of a botanical raw material, or herbal preparation.
However, a marker compound is a chemical constituent that is also used for identification and/or standardisation processes, especially when the active constituents are not known or identified. Chemical standardisation often involves chemical identification by spectroscopic or chromatographic fingerprint techniques, and quantitative analysis for active constituents or marker compounds if available.
The key challenges in the development of analytical methods for botanicals and herbal preparations are:
(a) Analysis of active compounds or markers in a complex or crude extract,
(b) Lack of standard reference substances,
(c) Target analytes may be thermally labile,
(d) Selection of extraction and separation methods, and
(e) Batch-to- batch variation of the composition of the plant material obtained.
The analytical methods developed should be validated. With the chemical fingerprint, the method should be able to perform composition analysis and monitor the batch-to- batch variation of the plant materials obtained for use.
Methods that are simple, rapid and environmentally friendly are attractive options for the user. For the analysis of botanicals and herbal preparations, a holistic solution involving the combination of the methods of extraction, separation and analytical techniques are required.