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Friday, 16 May 2014

Phytomedicine

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Medicinal Plant

Plants are invaluable in the quest for new drugs. There is a tremendous historical legacy in traditional uses of plants, parts of plants and isolated phytochemicals for the prevention, management and treatment of various health ailments (Oloyede et al., 2012). Scientific studies on plants used in ethnomedicine led to the discovery of many valuable drugs like taxol, vincristine and vinblastine (Sahoo et al., 2010).

During the past decade, there has been increasing public interest and acceptance of traditional medicine in both developing and developed countries.

Due to poverty and limited access to modern medicine, about 80% of the world’s population, especially in the developing countries uses herbal medicine as their source of primary healthcare (Farnsworth et al., 1985; Bisset, 1994; Mukherjee, 2002; Bodeker et al., 2005). In these communities, traditional medical practice is often viewed as an integral part of their culture. In Nigeria, people are attracted to herbal therapies for many reasons, the most important reason being that, like our ancestors, it is believed they will help us live healthier lives. Herbal medicines are often viewed as a balanced and moderate approach to healing. Individuals now use them as remedies and spend billions of dollars on herbal products. As such, they now represent a substantial proportion of the global drug market (Farnsworth et al., 1985; Roberts and Tyler, 1997; Blumenthal et al., 1998; Blumenthal, 2000; WHO, 2005).

To achieve the desired benefit from herbal preparations, an individual must take the required dose over a certain length of time. Although it is generally believed that most herbal preparations are safe for consumption, some herbs like most biologically active substances could be toxic with undesirable side effects (Bisset, 1994).

The variability of the constituents in herbs or herbal preparations due to genetic, cultural and environmental factors has made the use of herbal medicines more challenging than it would necessarily have been. For instance, the availability and quality of the raw materials are frequently problematic, the active principles are diverse and may be unknown, and quality of different batches of preparation may be difficult to control and ascertain. In most countries, herbal products are launched into the market without proper scientific evaluation, and without any mandatory safety and toxicological studies. There is no effective machinery to regulate manufacturing practices and quality standards. Consumers can buy herbal products without a prescription and might not recognize the potential hazards in an inferior product. A well-defined and constant composition of the drug is therefore, one of the most important prerequisites for the production of a quality drug. Given the nature of products of plant origin, which are not usually constant and are dependent on and influenced by many factors, ensuring consistent quality of products is vital for the survival and success of the industry (Bauer, 1998).

Terms in herbal medicines

The terms and their definitions have been selected and adopted from WHO General Guidelines for Methodologies on Research and Evaluation of Traditional Medicine (2000).

1. Medicinal plant

A plant, either growing wild or cultivated, used for its medicinal purposes.

2. Herbal medicines

These include herbs, herbal materials, herbal preparations and finished herbal products:

3. Herbs

Herbs include crude plant material such as leaves, flowers, fruit, seeds, stems, wood, bark, roots, rhizomes or other plant parts, which may be entire, fragmented or powdered.

4. Herbal materials

Herbal materials are either whole plants or parts of medicinal plants in the crude state. They include herbs, fresh juices, gums, fixed oils, essential oils, resins and dry powders of herbs. In some countries, these materials may be processed by various local procedures, such as steaming, roasting, or stir baking with honey, alcoholic beverages or other materials.

5. Herbal preparations

Herbal preparations are the basis for finished herbal products and may include comminuted or powdered herbal materials, or extracts, tinctures and fatty oils, expressed juices and processed exudates of herbal materials.

They are produced with the aid of extraction, distillation, expression, fractionation, purification, concentration, fermentation or other physical or biological processes. They also include preparations made by steeping or heating herbal materials in alcoholic beverages and/or honey, or in other materials.

6. Finished herbal products or herbal medicinal products

Medicinal products containing as active substances exclusively herbal drugs or herbal drug preparations. They may consist of herbal preparations made from one or more herbs. If more than one herb is used, the term mixed herbal product can also be used. They may contain excipients in addition to the active ingredients. In some countries herbal medicines may contain, by tradition, natural organic or inorganic active ingredients, which are not of plant origin (e.g. animal materials and mineral materials). Generally however, finished products or mixed products to which chemically defined active substances have been added, including synthetic compounds and/or isolated constituents from herbal materials, are not considered to be herbal.

 

The Effects of Phytomedicines

In contrast to synthetic pharmaceuticals based upon single chemicals, many phytomedicines exert their beneficial effects through the additive or synergistic action of several chemical compounds acting at single or multiple target sites associated with a physiological process. As pointed out by Tyler (1999), this synergistic or additive pharmacological effect can be beneficial by eliminating the problems associated with a single xenobiotic compound in the body. In another report, Kaufman et al. (1999) extensively documented how synergistic interactions underlie the effectiveness of a number of phytomedicines. This theme of multiple chemicals acting in an additive or synergistic manner likely has its origin in the functional role of secondary products in promoting plant survival. For example, in the role of secondary products as defense chemicals, a mixture of chemicals having additive or synergistic effects at multiple target sites would not  only ensure effectiveness against a wide range of herbivores or pathogens but would also decrease the chances of these organisms developing resistance or adaptive responses (Kaufman et al., 1999; Wink, 1999).

An estimated 4 billion inhabitants of the world, that is about 80% of world’s population, are thought to rely chiefly on traditional medicine, which is largely of plant origin, for their primary health care needs (Norman, et al., 1985). However, it is widely believed that these valuable medicinal resources in plants are largely untapped because of inadequate scientific technical and commercial infrastructures in developing countries (Olayiwola, 1993).

In recent years, there is a growing interest in herbal therapy. Data on scientific screening of plant extracts, whether crude or purified, appears to be accumulating gradually. The major contributory factors to this growing interest include:

i)    Rising costs of orthodox medications

ii)   Low therapeutic index of synthetic compounds and

iii) The growing incidence of drug resistance (Onyeyilli and Egwu, 1995; Seed, 2000) among the pathogens especially in developing countries with very weak economic indices.

It is thought that the use of plant-derived active principles will offer people access to safe and effective products for the prevention and treatment of diseases through self-medication.

 

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