pharmacognosy 15

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PHG 456:

PHG 456 Evaluation of Vegetable and Animal Drugs


Introduction According to the World Health Organization (WHO), because of poverty and lack of access to modern medicine, about 65-80 % of the world’s population which lives in developing countries depends essentially on plants for primary health care. Currently, the major pharmaceutical companies have demonstrated renewed interest in investigating higher plants as sources for new lead structures and also for the development of standardized phytotherapeutic agents with proved efficacy, safety and quality. Herbal medicinal preparations are normally very popular in developing countries with a long tradition in the use of medicinal plants and also in some developed countries such as Germany, France, Italy and the United States where appropriate guidelines for registration of such medicines exist.

Definition and main characteristics of herbal medicines (phytotherapeutic agents):

Phytotherapeutic agents or phytomedicines are standardized herbal preparations consisting of complex mixtures of one or more plants which are used in most countries for the management of various diseases. According to the WHO definition, herbal drugs contain as active ingredients plant parts or plant materials in the crude or processed state plus certain excipients, i.e., solvents, diluents or preservatives. Usually, the active principles responsible for their pharmacological action are unknown. One basic characteristic of phytotherapeutic agents is the fact that they normally do not possess an immediate or strong pharmacological action. For this reason, phytotherapeutic agents are not used for emergency treatment. Definition and main characteristics of herbal medicines (phytotherapeutic agents)

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Other characteristics of herbal medicines are their wide therapeutic use and great acceptance by the population. In contrast to modern medicines, herbal medicines are frequently used to treat chronic diseases. Combinations with chemically defined active substances or isolated constituents are not considered to be herbal medicines. It is important to note that, although homeopathic preparations may frequently contain plants, they are also not considered to be herbal medicines. Conditions for which consumers use phytomedicines in Germany, a country where herbal drugs are widely used, include: common cold (66%), flu (38%), digestive and/or intestinal diseases (25%), headache (25%), insomnia (25%), stomach ulcer (34%), nervousness (21%), circulatory disorders (15%), bronchitis (15%), skin diseases (15%), and fatigue and exhaustion (12%). However, so far, relatively few herbal drugs have been evaluated scientifically to prove their safety, potential benefits and effectiveness. The sources of raw material and the good practices of manufacturing processes are certainly the essential steps for the quality control of herbal medicines.

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Phytotherapeutic agents are normally marketed as standardized preparations in the form of liquid, solid (powdered extract), or viscous preparations. They are prepared by maceration, percolation or distillation (volatile oils). Ethanol, water, or mixtures of ethanol and water are used for the production of fluid extracts. Solid or powdered extracts are prepared by evaporation of the solvents used in the process of extraction of the raw material. Some phytotherapeutic agents are greatly concentrated in order to improve their therapeutic efficacy. The standardized powder extract of Ginkgo biloba (50:1), for instance, means that 50 parts of raw material were processed to yield 1 part of standardized powder extract. In this process, it is also possible to remove, when necessary, some secondary metabolites present in the plants which may produce undesirable side effects.

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Compared with well-defined synthetic drugs, herbal medicines exhibit some marked differences, namely: the active principles are frequently unknown; standardization, stability and quality control are feasible but not easy; the availability and quality of raw materials are frequently problematic; well-controlled double-blind clinical and toxicological studies to prove their efficacy and safety are rare; empirical use in folk medicine is a very important characteristic; they have a wide range of therapeutic use and are suitable for chronic treatments; the occurrence of undesirable side effects seems to be less frequent with herbal medicines, but well-controlled randomized clinical trials have revealed that they also exist; they usually cost less than synthetic drugs.

The worldwide herbal medicine market and the main causes for the increased interest in herbal medicines:

The worldwide herbal medicine market and the main causes for the increased interest in herbal medicines During the past decades, public interest in natural therapies, namely herbal medicine, has increased dramatically not only in developing countries but mainly in industrialized countries. This has increased the international trade in herbal medicine enormously and has attracted most of the pharmaceutical companies, including the multinationals. Until a few years ago, only small companies had interest in the marketing of herbal medicines. Currently, most large multinational companies are interested in commercializing herbal drugs. It is estimated that the European market alone reached about $7 billion in 1997. The German market corresponds to about 50% of the European market, about $3.5 billion. This market is followed by France, $1.8 billion; Italy, $700 million; the United Kingdom, $400 million; Spain, $300 million; the Netherlands, about $100 million. European herbal medicines are distributed under 6 basic therapeutic categories: cardiovascular, 27.0%; respiratory, 15.3%; digestive, 14.4%; tonic, 14.4%; hypnotic/sedative, 9.3%; topical, 7.4%; others, 12.0%.

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The herbal medical database indicates that the herbal medicine markets in Asia and Japan reach $2.3 and 2.1 billion, respectively. However, in no other country has the herbal medicine marketplace grown more than it has in the in USA. A few years ago, this was a non-existent category of medicine. The US herbal medicine market reached about $3.2 billion in 1996, and $5 billion in 1999. According to a national survey, about 60 million Americans over 18 years of age use herbal drugs to treat colds, burns, headaches, allergies, rashes, depression, diarrhea and menopause, among others. Currently, most medicinal herbs, such as Aloe vera , Panax quinquefolius (American ginseng ) , Echinacea, Alium sativum , Ginkgo biloba , Serenoa repens (saw palmetto), Valeriana officinalis , etc., are cultivated in the USA and exported to Europe and the Orient. As a natural consequence, many large companies have introduced a line of herbal products into their sales.

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The phytomedicine market has grown at an expressive rate worldwide since 1985 (from 5 to 18% a year). Several important factors have contributed to the growth of this worldwide phytotherapeutic market, among which the following may be mentioned: preference of consumers for natural therapies; concern regarding undesirable side effects of modern medicines and the belief that herbal drugs are free from side effects, since millions of people all over the world have been using herbal medicines for thousands of years; great interest in alternative medicines; preference of populations for preventive medicine due to increasing population age; the belief that herbal medicines might be of effective benefit in the treatment of certain diseases where conventional therapies and medicines have proven to be inadequate; tendency towards self-medication; improvement in quality, proof of efficacy and safety of herbal medicines; high cost of synthetic medicines.

Standardization of botanical herbs and quality of botanical preparations:

Standardization of botanical herbs and quality of botanical preparations Plants contain several hundred constituents and some of them are present at very low concentrations. In spite of the modern chemical analytical procedures available, only rarely do phytochemical investigations succeed in isolating and characterizing all secondary metabolites present in the plant extract. Apart from this, plant constituents vary considerably depending on several factors that impair the quality control of phytotherapeutic agents. Quality control and standardization of herbal medicines involve several steps. However, the source and quality of raw materials play a pivotal role in guaranteeing the quality and stability of herbal preparations. Other factors such as the use of fresh plants, temperature, light exposure, water availability, nutrients, period and time of collection, method of collecting, drying, packing, storage and transportation of raw material, age and part of the plant collected, etc., can greatly affect the quality and consequently the therapeutic value of herbal medicines.

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Some plant constituents are heat labile and the plants containing them need to be dried at low temperatures. Also, other active principles are destroyed by enzymatic processes that continue for long periods of time after plant collection. This explains why frequently the composition of herbally based drugs is quite variable. Thus, proper standardization and quality control of raw material and the herbal preparations themselves should be permanently carried out. In the cases where the active principles are unknown, marker substance(s) should be established for analytical purposes. However, in most cases these markers have never been tested to see whether they really account for the therapeutic action reported for the herbal drugs. As pointed out before, apart from these variable factors, others such as the method of extraction and contamination with microorganisms, heavy metals, pesticides, etc., can also interfere with the quality, safety and efficacy of herbal drugs.

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For these reasons, pharmaceutical companies prefer using cultivated plants instead of wild-harvested plants because they show smaller variation in their constituents. Furthermore and certainly more relevant, when medicinal plants are produced by cultivation, the main secondary metabolites can be monitored and this permits definition of the best period for harvesting. The recent advances which occurred in the processes of purification, isolation and structure elucidation of naturally occurring substances have made it possible to establish appropriate strategies for the analysis of quality and the process of standardization of herbal preparations in order to maintain as much as possible the homogeneity of the plant extract. Among others, thin-layer chromatography, gas chromatography, high-performance liquid chromatography, mass spectrometry, infrared-spectrometry, ultraviolet/visible spectrometry, etc., used alone or in combination, can be successfully used for standardization and to control the quality of both the raw material and the finished herbal drugs.

Regulatory aspects and approval of herbal drugs:

Regulatory aspects and approval of herbal drugs The legal process of regulation and legislation of herbal medicines changes from country to country. The reason for this involves mainly cultural aspects and also the fact that herbal medicines are rarely studied scientifically. Thus, few herbal preparations have been tested for safety and efficacy. The WHO has published guidelines in order to define basic criteria for evaluating the quality, safety, and efficacy of herbal medicines aimed at assisting national regulatory authorities, scientific organizations and manufacturers in this particular area. Furthermore, the WHO has prepared pharmacopeic monographs on herbal medicines and the basis of guidelines for the assessment of herbal drugs.

Regulatory aspects and approval of herbal drugs in USA :

Regulatory aspects and approval of herbal drugs in USA Since 1994, herbal medicines have been regulated under the “Dietary Supplement Health and Education Act of 1994”. On the basis of this law, herbal medicines are not evaluated by the Food and Drug Administration and, most important, these products are not intended to diagnose, treat, cure, or prevent diseases. The US government has established the “Office of Alternative Medicine” at the National Institutes of Health (NIH) with the following aims: 1) to explore the potential role of dietary supplements in the improvement of health; 2) to promote the scientific study of supplements for maintaining health and preventing chronic diseases; 3) to compile a database of scientific research related to supplements; 4) to coordinate NIH funding for dietary supplements related to the treatment of chronic disease.

Regulatory aspects and approval of herbal drugs in Germany:

Regulatory aspects and approval of herbal drugs in Germany Germany’s Commission E (phytotherapy and herbal substances) was established in 1978. It is an independent division of the German Federal Health Agency that collects information on herbal medicines and evaluates them for safety and efficacy. The following methods and criteria are followed by Commission E: 1) traditional use; 2) chemical data; 3) experimental, pharmacological and toxicological studies; 4) clinical studies; 5) field and epidemiological studies; 6) patient case records submitted from physician’s files, and 7) additional studies, including unpublished proprietary data submitted by manufacturers.

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The composition of Commission E is as follows: physicians, pharmacists, pharmacologists (pharmacognosist), toxicologists, industry representatives and laypersons, for a total of 24 members. Two possibilities for marketing herbal drugs exist: 1) temporary marking authorization for old herbal drugs until they are evaluated for safety and efficacy; and 2) monographs of standardized marketing authorization. Evaluations are published in the form of monographs that approve or disapprove the herbal drugs for use. Herbal medicines are sold in pharmacies, drugstores and health food stores. Some herbal medicines are controlled by a physician’s prescription. Commission E has published about 300 monographs and about 600-700 plants are sold in Germany. Approximately 70% of physicians prescribe registered herbal drugs. Part of annual sales is paid for by government health insurance.

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