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Parameters for Quality Control of Herbal Drugs
Quality control of phytomedicine
The quality control of phytopharmaceuticals may be defined as the status of a drug, which is determined either by identity, purity, content, and other chemical, physical or biological properties, or by the manufacturing process.
Quality control is based on three important pharmacopeial definitions:
• Identity: Is the herb the one it should be?
• Purity: Are there contaminants, e.g., in the form of other herbs which should not be there?
• Content or assay: Is the content of active constituents within the defined limits?
Parameters for Quality Control of Herbal Drugs
1 Microscopic Evaluation
Quality control of herbal drugs has traditionally been based on appearance and today microscopic evaluation is indispensable in the initial identification of herbs, as well as in identifying small fragments of crude or powdered herbs, and detection of foreign matter and adulterants. A primary visual evaluation, which seldom needs more than a simple magnifying lens, can be used to ensure that the plant is of the required species, and that the right part of the plant is being used. At other times, microscopic analysis is needed to determine the correct species and/or that the correct part of the species is present. For instance, pollen morphology may be used in the case of flowers to identify the species, and the presence of certain microscopic structures such as leaf stomata can be used to identify the plant part used. Although this may seem obvious, it is of prime importance, especially when different parts of the same plant are to be used for different treatments. Stingin nettle (Urtica urens) is a classic example where the aerial parts are used to treat rheumatism, while the roots are applied for benign prostate hyperplasia.
2 Determination of Foreign Matter
Herbal drugs should be made from the stated part of the plant and be devoid of other parts of the same plant or other plants. They should be entirely free from moulds or insects, including excreta and visible contaminant such as sand and stones, poisonous and harmful foreign matter and chemical residues. Animal matter such as insects and “invisible” microbial contaminants, which can produce toxins, are also among the potential contaminants of herbal medicines . Macroscopic examination can easily be employed to determine the presence of foreign matter, although microscopy is indispensable in certain special cases (for example, starch deliberately added to “dilute” the plant material). Furthermore, when foreign matter consists, for example, of a chemical residue, TLC is often needed to detect the contaminants .
3 Determination of Ash
To determine ash content the plant material is burnt and the residual ash is measured as total and acid-insoluble ash. Total ash is the measure of the total amount of material left after burning and includes ash derived from the part of the plant itself and acid-insoluble ash. The latter is the residue obtained after boiling the total ash with dilute hydrochloric acid, and burning the remaining insoluble matter. The second procedure measures the amount of silica present, especially in the form of sand and siliceous earth .
4 Determination of Heavy Metals
Contamination by toxic metals can either be accidental or intentional. Contamination by heavy metals such as mercury, lead, copper, cadmium, and arsenic in herbal remedies can be attributed to many causes, including environmental pollution,and can pose clinically relevant dangers for the health of the user and should there-fore be limited . The potential intake of the toxic metal can be estimated on the basis of the level of its presence in the product and the recommended or estimated dosage of the product. This potential exposure can then be put into a toxi-cological perspective by comparison with the so-called Provisional Tolerable Week-ly Intake values (PTWI) for toxic metals, which have been established by the Foodand Agriculture Organization of the World Health Organization (FAO-WHO)
A simple, straightforward determination of heavy metals can be found in many pharmacopoeias and is based on color reactions with special reagents such as thioacetamide or diethyldithiocarbamate, and the amount present is estimated by comparison with a standard. Instrumental analyses have to be employed when the metals are present in trace quantities, in admixture, or when the analyses have to be quantitative. The main methods commonly used are atomic absorption spectrophotometry (AAS), inductively coupled plasma (ICP) and neutron activation analysis (NAA) .
5 Determination of Microbial Contaminants and Aflatoxins
Medicinal plants may be associated with a broad variety of microbial contaminants, represented by bacteria, fungi, and viruses. Inevitably, this microbiological background depends on several environmental factors and exerts an important impact on the overall quality of herbal products and preparations. Risk assessment of the microbial load of medicinal plants has therefore become an important subject in the establishment of modern Hazard Analysis and Critical Control Point (HACCP) schemes.
Herbal drugs normally carry a number of bacteria and molds, often originating in the soil. Poor methods of harvesting, cleaning, drying, handling, and storage may also cause additional contamination, as may be the case with Escherichia coli or Salmonella spp. While a large range of bacteria and fungi are from naturally occurring microflora, aerobic spore-forming bacteria frequently predominate.
Laboratory procedures investigating microbial contaminations are laid down in the well-known pharmacopoeias, as well as in the WHO guidelines . Limit
values can also be found in the sources mentioned. In general, a complete procedure consists of determining the total aerobic microbial count, the total fungal count, and the total Enterobacteriaceae count, together with tests for the presence of Escherichia coli, Staphylococcus aureus, Shigella, and Pseudomonas aeruginosa and Salmonella spp. The European Pharmacopoeia also specifies that E. coli and Salmonella spp. should be absent from herbal preparations . However it is not always these two pathogenic bacteria that cause clinical problems. For example, a fatal case of listeriosis was caused by contamination of alfalfa tablets with the Grampositive bacillus Listeria monocytogenes.
Materials of vegetable origin tend to show much higher levels of microbial contamination than synthetic products and the requirements for microbial contamination in the European Pharmacopoeia allow higher levels of microbial contamination in herbal remedies than in synthetic pharmaceuticals. The allowed contamination level may also depend on the method of processing of the drug. For example, higher contamination levels are permitted if the final herbal preparation involves boiling with water .The presence of fungi should be carefully investigated and/or monitored, since some common species produce toxins, especially aflotoxins. Aflatoxins in herbal drugs can be dangerous to health even if they are absorbed in minute amounts . Aflatoxin-producing fungi sometimes build up during storage . Procedures for the determination of aflatoxin contamination in herbal drugs are published by the WHO . After a thorough clean-up procedure, TLC is used for confirmation.
In addition to the risk of bacterial and viral contamination, herbal remedies may also be contaminated with microbial toxins, and as such, bacterial endotoxins and mycotoxins, at times may also be an issue . There is evidence that medicinal plants from some countries may be contaminated with toxigenic fungi (Aspergillus, Fusarium). Certain plant constituents are susceptible to chemical transformation by contaminating microorganisms.Withering leads to enhanced enzymic activity, transforming some the constituents to other metabolites not initially found in the herb. These newly formed constituent(s) along with the molds such as Penicillium nigricans and P. jensi may then have adverse effects.
6 Determination of Pesticide Residues
Even though there are no serious reports of toxicity due to the presence of pesticides and fumigants, it is important that herbs and herbal products are free of these chemicals or at least are controlled for the absence of unsafe levels.
Herbal drugs are liable to contain pesticide residues, which accumulate from agricultural practices, such as spraying, treatment of soils during cultivation, and administering of fumigants during storage. However, it may be desirable to test herbal drugs for broad groups in general, rather than for individual pesticides. Many pesticides contain chlorine in the molecule, which, for example, can be measured by analysis of total organic chlorine. In an analogous way, insecticides containing phosphate can be detected by measuring total organic phosphorus.
Samples of herbal material are extracted by a standard procedure, impurities are removed by partition and/or adsorption, and individual pesticides are measured by GC, MS, or GC/MS. Some simple procedures have been published by the WHO and the European Pharamacopoeia has laid down general limits for pesticide residues in medicine.
7 Determination of Radioactive Contamination
There are many sources of ionization radiation, including radionuclides, occurring in the environment. Hence a certain degree of exposure is inevitable. Dangerous contamination, however, may be the consequence of a nuclear accident. The WHO, in close cooperation with several other international organizations, has developed guidelines in the event of a widespread contamination by radionuclides resulting from major nuclear accidents. These publications emphasize that the health risk, in general, due to radioactive contamination from naturally occurring radio nuclides is not a real concern, but those arising from major nuclear accidents such as the nuclear accident in Chernobyl, may be serious and depend on the specific radionuclide, the level of contamination, and the quantity of the contaminant consumed. Taking into account the quantity of herbal medicine normally consumed by an individual, they are unlikely to be a health risk. Therefore, at present, no limits are proposed for radioactive contamination.