Standardisation of Herbal Medicines

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.