Medicinal herbs constitute an important source for traditional systems of medicine (ayurveda, homoeopathy, siddha, Chinese medicine and herbalism) and synthetic system of medicine. In rural areas, 75 percent of the population is dependent on herbal medicines for healthcare. A study from America demonstrated that 34 percent of the patients used one or the other system at least once a year. Herbals or natural products are becoming popular which can be attributed to the belief that they are safe.
The herbal drug industry is considered to be a high growth industry of the late 90s and seeing the growing demand, it is all set to flourish in the next century. The trend for the increasing popularity of medicinal herbs in countries like America, Australia and Germany is well supported by statistical data. Ayurveda, the ancient Indian system of medicine, strongly believes in polyherbal formulations and scientists of modern era often ask for scientific validation of herbal remedies.
The crude medicinal herbs have long been cultivated and traded in many countries around the world. The drugs are either supplied in dried or powdered form. The medicinal herb is a biosynthetic laboratory as it contains number of chemical compounds like glycosides, alkaloids, resins etc. These compounds exert therapeutic effect and account for medicinal property of the medicinal herb. Clinical studies have shown that medicinal herbs used without medical supervision can be the cause of hepatotoxicity or potential drug interactions.
The efficacy of some herbal products is beyond doubt, the most recent examples being Artemisia Annua (artemesinin), Taxus Brevifolia (taxols) and Silybium marianum (Silymarin). Hypericum Perforatum (hypericin & hyperforin), Allium Sativum (allicin or allin), Ginkgo biloba (Ginkgolic acid) are popularly used herbal remedies among people. All these herbals are standardized for active constituent. Standardization means adjusting the herbal drug preparation to a defined content of the active constituent. Extract refers to a concentrated preparation of active constituent of a medicinal herb. The concept of standardized extracts definitely provides a solid platform for scientific validation of herbals.
Another concept sweeping the herbal drug industry is identification of marker compounds in the extract. Markers constitute chemically defined constituents, which are used for control purpose. Markers may or may not have therapeutic activity. The markers can serve as a powerful tool in the finished form of herbal drug preparations, which depends upon the quantitative determination of the marker, when the starting material is selected. Hypericum perforatum (St John''s wort) is recent example for an extract, where marker compound (hypericin) and therapeutic constituent (hyperforin), both are known.
Phytochemistry deals with the determination of chemical constituents in plant material. Chemical analysis of the plant material is a critical factor for standardization. Techniques like High Performance Liquid Chromatography (HPLC), Gas Chromatography (GC) and High Performance Thin Layer Chromatography (HPTLC) are commonly used for chemical finger print analysis. Standardized extracts provide a consistent and effective alternative to crude drugs, as they constitute calculated ratio of the active constituents. The concept of standardization is now being widely welcomed and it is a rational way to increase the acceptance of medicinal herbs among the physicians and patients.
Most of the herbal extracts are made from crude herbs; they can vary in percentage of active constituents, which further influences the therapeutic activity of herbs. Depending upon the source, the variation in the chemical composition of the medicinal plants is enormous, a possible cause of inconsistent therapeutic effects of herbal products. Faced with the distribution of toxic constituents in herbs and the practice of self- medication, physicians as well as patients should be careful with potentially toxic plant constituents. Tussilago Farfara, Arctostaphylos uva-ursi, Heliotropium Eichwaldii contain hepatotoxic pyrrolizidine alkaloids, Solanum Nigrum (solanine), Ricinus Communis (ricin), Acorus Calamus (acoretin) have been discovered to constitute toxic principles.
Ayurveda is a potential source of indigenous drugs. A number of medicinal herbs like Rauwolfia Serpentina (reserpine), Vinca Rosea (vinblastine & vincristine), Cassia Angustifolia (sennosides), Atropa Belladonna (atropine), Papaver Somniferum (morphine) and Digitalis pupurea (digoxin) have provided the modern science with potent weapons. These medicinal herbs became popular due to single active constituents. Keeping in mind the overall scenario, only selected medicinal herbs have been used in standardized from and market analysis clearly favors them.
Polyherbal formulations as mentioned in classical texts of Ayurveda, are used by number of pharmaceutical companies. It is very difficult to understand the theme of polyherbal preparations as a number of ingredients may vary from two to 25 or more. It is very difficult to set the standards of these types of formulations. The situation is further worsened by the multiple use of these formulations as mentioned in Ayurveda. Keeping in view the growing popularity of herbals, it is the need of hour to have analytical data, bio-equivalence, pharmacological, toxicological studies with particular reference to herbal-synthetic drug interactions. This is possible only if standardised extracts concentrated to known therapeutic constituents are used.
The concept of standardization is finally catching up with Ayurvedic herbs and some of them have been standardized. The standardized Ayurvedic herbs are:
1. Adhatoda vasica (0.5% Vasicine )
2. Andrographis Paniculata (10% Andrographolide)
3. Azadirachita Indica 2% (Azadiractin)
4. Bacopa Monneri 20% (Bacoside)
5. Boswellia Seratta (40% and 70% Boswellic Acid).
6. Centella Asiatica (3% Asiaticoside)
7. Commiphora Mukul (5% Guggulsterones)
8. Curcuma longa(95% Curcumin)
9. Embelia Ribes (8% Embellin)
10. Glycyrrihiza Glabra (20% Glycyrrhizin)
11. Gymnema Sylvestre (25% Gymnemic Acid).
12. Momordica Charantia (3% bitters).
13. Phylanthus Niruri (2% bitters)
14. Picrorrhiza Kurroa (10% bitters )
15. Shilajit (5% Fulvic Acid)
16. Tribulus Terrestris (20% and 40% Saponin)
17. Trigonella Foenum Graceum (10% Saponin)
18. Withania Somnifera (1.5% withanolides / 1% Alkaloid).
19. Zingiber Officinale (5% Gingerols).
British herbal pharmacopoeia, American herbal pharmacopoeia & German commission E have prescribed certain specifications regarding herbal drugs. These include
* ''The herbal drug or herbal preparation in its entirety is regarded as the active substance''.
* Constituents with known activity ''are chemically defined substances or group of substances which are generally accepted to contribute substantially to the therapeutic activity of a herbal drug or of a preparation.''
* Makers ''are chemically defined constituents of an herbal drug, which are of interest for control purposes.
* Standardization refers to '' adjusting the herbal drug preparation to a defined content of a constituent or a group of substances with known therapeutic activity.
* A specification is defined as a list of tests, reference to analytical and biological procedures and appropriate acceptance criteria, which are numerical limits, ranges or other criteria for the test described.
Ayurvedic Pharmacopoeia has also indicated standards for crude drugs like sampling (preliminary examination, foreign matter, quantitative microscopy), moisture content (loss on drying, separation and measurement of moisture, chemical method [Karl Fischer Method] extractive value, ash value, swelling index (applicable to mucilage containing drugs), chromatographic studies of standardized extracts etc. These standards are of further importance as they control the nature of the extract to be manufactured and standardized.
About the authors :
The author is Medical Executive, Super Speciality Division, Ind -Swift Ltd