14: Herb Manufacture, Pharmacy, and Dosing

CHAPTER 14 Herb Manufacture, Pharmacy, and Dosing



Aplethora of products is available on the market. Why wouldn’t we simply recommend that our clients go and buy one off the shelf for their animal? Quite apart from the standard practice of prescribing according to individual needs, one of our main concerns is whether the practitioner can be confident of product quality. Is it safe? Will it be effective? Quality control is covered in Chapter 8, and integral to this is the matter of how herbs are manufactured. This chapter looks at how herbs are made into various useful forms and how they can be dispensed and dosed appropriately.




GOOD MANUFACTURING PRACTICE


To know which herbs a patient is receiving, practitioners must make their own or purchase good-quality herbal medicines and formulate from these. Manufacture of herbal medicinal products should be undertaken according to Good Manufacturing Practice (GMP), with the goal of providing quality assurance and safety in all manufactured products. It is important to know that the chosen manufacturer complies with these standards, which ensure that the right species is being used, that it is being produced and stored properly, and that it is not contaminated or adulterated.


Compared with well-defined synthetic drugs, herbal medicines exhibit some marked differences, namely,







It is no surprise that manufacture of herbal products under GMP is more complex than that of conventional drugs. However, GMP is not applied to growing, harvesting, drying, or sifting of herbs, nor is it related to preliminary processing of herbal oils. So, the sources of raw material and the good practices of manufacturing processes are certainly essential steps in the quality control of herbal medicines. One critical issue for safety and efficacy is identification of the right plant species. Substitution of one herbal raw material for another can be a serious problem when it is a subspecies, the wrong species (e.g., Aristolochia for Stephania causing renal failure), or a less active plant part, or when an herb is contaminated by another species (e.g., digitalis in comfrey).


Therefore, it is important that material specifications for crude herbs should include information on source, part used, description, and identification, as well as reports on contamination with pesticides, microbes, mould, pests, or foreign matter and on purity or potency. Herbs have been contaminated with heavy metals (e.g., cadmium and arsenic) and have been adulterated with drugs (e.g., nonsteroidal anti-inflammatory drugs). Any contamination could compromise the safety and efficacy of an herbal preparation, even when the practitioner decides to make his or her own herbs in practice; a specification form should be requested when bulk purchases are made.


In the first instance then, the source and quality of raw materials play a pivotal role in the quality and stability of herbal preparations. Other factors such as use of fresh or dried plants, season, light exposure, water availability, nutrients, period and time of collection, storage and transportation of raw material, age and part of the plant collected, and methods of collecting, drying, and packing can greatly affect the quality and consequently the therapeutic value of herbal medicines. These factors also account for variability of individual constituents or markers in herbal preparations. This variability is not a feature of conventional drug manufacture.



STANDARDIZATION


The American Herbal Products Association (AHPA) defines standardization very broadly as “the complete body of information and controls that serves to optimize the batch-to-batch consistency of a botanical product. Standardization is achieved by reducing the inherent variation of natural product composition through quality assurance practices applied to agricultural and manufacturing processes.”


Standardized extracts are common in trade and 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 solvents used in the process of extraction of the raw material.


Advances in the processes of purification, isolation, and measuring of certain phytochemicals have made possible the establishment of appropriate strategies for the analysis of quality and the process of standardization of herbs toward maintaining as much as possible the homogeneity of the plant extract. Among others, gas chromatography, high-performance liquid chromatography, thin-layer chromatography, mass spectrometry, infrared spectrometry, and ultraviolet/visible spectrometry, used alone or in combination, can be successfully used for standardization and to control the quality of the raw material and the finished herbal products.


However, plants contain several hundred constituents, and some of them are present at very low concentrations; despite these technologically advanced chemical analytical procedures, rarely do phytochemical investigations succeed in isolating and characterizing all secondary metabolites present within a plant extract. Also, marker substances used in standardization and quality control tests may not really account for the therapeutic action reported for an herbal product.


As well, marker compounds may exhibit wide variation, for example, Echinacea purpurea products in Australian products have demonstrated wide variation in such markers as alkylamides and caffeoyl phenols. Thus, standardization and quality control of raw material and herbal preparations are challenging compared with these processes in standard drug manufacturing, and their relevance to therapeutic value may be questionable. Standardization can enhance only the reproducibility of a preparation—not its quality.


The AHPA white paper on standardization notes that the concept of standardization has been misunderstood to describe the “control or isolation of particular constituents. On the contrary, standardization is a complex, multifaceted process that relies primarily on appropriate controls of raw materials and the manufacturing process. Quantitative testing such as bioassays or measurement of specific constituents may be used in addition to, but never in place of, these other measures, because analytical measurements by themselves can only confirm, not control, “batch-to-batch consistency.”



SOURCES OF HERBS


Commercial herbal preparations draw plant material from two main sources: wildcrafting and cultivation. Wildcrafting involves the harvesting of plants from the wild by trained collectors; these herbs are preferred by many herbalists. Cultivated plants are specifically grown for the trade and are the best sources of endangered or threatened herbs. Herbalists and especially herb pharmacies have voiced concern that plants in cultivation are not of the same quality as wildcrafted herbs. Herb pharmacies are investigating this issue in partnership with academic centers; no clear answers have been revealed as yet.


Wildcrafting has led to the endangerment of a number of herbs, including goldenseal and ginseng. There is concern about others—even wild echinacea in the United States and thyme in Europe. Some herbs have very limited habitats, and although they are not now endangered, they are subject to trends and shifts in popularity. When herbs are bought from a supplier who wildcrafts, the purchaser should make sure that the label says “ethically wildcrafted.” This means that the wildcrafter protects the herbs by harvesting only a small percentage. It is MUCH better for practitioners to find an organic cultivated source for these herbs.


A third source of herbs may be your own garden. Home production of locally endangered plants lightens the strain of commerce in that plant and provides the herbalist with an opportunity to better study his or her medicine from germination to patient administration. Even if regulatory pressures discourage veterinarians from assuming liability for their home-prepared herbal medicines, the use of home-grown plants in their own personal family pharmacy supports the learning process and is highly recommended for recreation and exercise. An excellent reference for home medicine-makers is Cech (2000).



FORMS OF HERBAL MEDICINES


Veterinarians are usually too busy to make their own herbal medicines, but it is important that they know how the herbs are prepared. Herbal products begin as fresh or dried plant, or as plant extracts (Box 14-1). These preparations form the basis for capsules, tablets, pills, salves, oils, liniments, juices, and tinctures.



Which form is commercially available or preferred depends upon whether the main constituents of an herb are lipid or water soluble, as well as on their palatability and level of patient acceptance. Whole fresh or dried plant is obviously the form that keeps all constituents intact, but it is the form that requires greater volume and may result in poor taste and potentially poor bioavailability; however, for ruminants and horses, this form may be the most acceptable.



Dried Forms



Dried herbs


Dried bulk herb has been harvested, dried, and sometimes powdered. Dried powdered herb may be supplied as a dried bulk herb, as loose powder, or in capsules. Gardeners may dry herbs from their own plots with basic knowledge of the plant part used and the correct harvest time. Aerial parts may be cut and bundled together to be hung on a rafter in a dry spot or on drying screens until dehydrated. A gentle air current can speed drying time, which cuts down on microbial contamination. The herb must be protected against excessive heat and light and not left exposed for long after it is dried. Once the herb is completely dried, it can be stripped from the stalks and stored in jars with lids, or in tins. This form can be used for teas or decoctions, or can be fed directly mixed in the animal’s food, which is probably ideal. Dried herbs are best stored under cold conditions (less than 11° C) to limit the hatching of insect eggs, which inevitably infest organic herbs.




US Pharmacopoeia (USP) Definitions


Fluid extract: Alcoholic or hydroalcoholic preparation providing a dry herb : liquid strength ratio of 1 : 1. These very concentrated extracts require vacuum equipment.


Fresh plant fluid extract: Alcoholic or hydroalcoholic tincture prepared using 1 part fresh herb by weight for 1 part liquid by volume. This weight : volume relationship takes into account the water content in fresh plants. (The AHPA adds that fluid extracts are also sometimes 1 : 2 biomass : solvent, and that traditionally dried herb is used.)


Soft extract: An extract that has the consistency of a thin to thick liquid or paste.


Solid extract: A USP fluid extract that has been evaporated or vacuum extracted to 4 parts herb for every 1 part extract.


Powdered extract: A powdered version of a USP solid extract or fluid extract, prepared by evaporation to remove liquid. The concentration can range from 1 : 1 to 10 : 1, or greater.


Standardized extract: A powdered extract prepared by any of the previous methods, with certain constituents (either a particularly active ingredient or a marker compound) standardized to a specific preset level in every batch of extract. These extracts may or may not change the ratio of constituent ingredients within the plant to each other, depending on which compound is chosen and how the plant is standardized.


Galenical extract: A pharmacopoeial extract prepared according to guidelines from various pharmacopoeias, such as the British Pharmaceutical Codex, that dictate the method of preparation, the solvent used (usually alcohol and water), and the ratio of herb material to final extract. In modern times, this extract is often formed into a tablet or capsule.




Tinctures and Liquid/Fluid Extracts


These are the most commonly dispensed liquid forms of herbs; combining liquids makes formulation and prescribing easy. The advantages of tinctures include the following:






Alcohol is a useful solvent and forms tinctures with nearly unlimited shelf-life, unless precipitation occurs over time. For extraction of water and lipid-soluble herb components, alcohol and water proportions may range from 20 : 80 to 40 : 60 (vodka is conveniently made this way) up to 100% alcohol. The percentage of alcohol needed varies according to the constituents to be dissolved, and good manufacturers vary the alcohol:water ratio to reflect the ideal extract for each individual herb (Table 14-1). For instance, mucilage does not dissolve well in ethanol, so a low alcohol percentage is best at 15% to 25%, and resinous herbs dissolve only in high-alcohol menstruum (90%+). Many herbs extract well in plain 80 proof (40% alcohol) vodka. Tinctures must contain at least 24% to 26% pure alcohol to be well preserved. Some manufacturers decoct herbs that are traditionally used this way (concentrated through multiple boiling water extractions), then preserve with alcohol.


TABLE 14-1 Solubility of Herb Components







































Component Example Plants Solubility
Alkaloids Goldenseal, lobelia, bloodroot, corydalis High solubility in alcohol, low water solubility. Vinegar may enhance extraction
Essential oils Peppermint, lavender, thyme, tea tree High solubility in alcohol, low water and glycerin solubility. Extract well into fixed oils
Glycosides Hawthorn, licorice, milk thistle, gentian Soluble in water and alcohol
Mucilage Slippery elm, marshmallow, purslane Water soluble only and best extracted in cold water; will precipitate if alcohol is added. Usually used fresh or simply dried
Polysaccharides Astragalus, mushrooms, boneset, echinacea Water soluble only, will precipitate if alcohol is added
Resins Kava, rosemary, grindelia, propolis, sweetgum Soluble in alcohol and hot oil; not soluble in water. To make an ointment, use tincture in 95%—100% alcohol; add oil, then gently heat to evaporate the alcohol
Saponins Ginseng, wild yam, yucca Water soluble
Tannins Witch hazel, blackberry leaf, self heals Water and glycerin soluble

One interesting variation on this theme is to extract some of the herb in 100% alcohol and decoct the other portion of herb, then add the two together at an optimal proportion; presumably, this allows maximal extraction of both water- and alcohol-soluble ingredients. It is wise to know what the concoction smells and tastes like when it is first made, so that one can check for spoilage later.


Alcohol extracts are concentrated and are believed by herbalists to have the most rapid gastrointestinal absorption rate and bioavailability of active components. It is likely that alcohol acts to keep these active components in solution after ingestion, thus facilitating their absorption into circulation. Alcohol extracts taste terrible to most dogs and cats, but the small amount required, in addition to the ease with which they can be combined by the herbalist, makes liquid extracts popular.




Making tinctures and fluid extracts


The folk method of preparing tinctures is simply to loosely pack a jar with fresh or dried cut herb, then to pour solvent over it to cover completely. To make a more standardized extract, the weight : volume method is used to describe the concentration of a tincture. The herb is weighed and the volume of the solvent is added in some proportion to the weight (grams of herb to milliliters of solvent, for instance), and typical proportions are 1 : 2 for fresh herb and 1 : 5 for dried herb. For example, 2 ounces by weight of an herb may be placed in a small jar, then covered with 4 oz of vodka, to produce a 40% alcohol 1 : 2 tincture. Strong herbs, such as lobelia and pokeweed, are often tinctured at lower concentrations (1 : 10) to guard against overdoses.


Tinctures are prepared with use of the herb (the “marc”) and a solvent (the “menstruum”). The herb is prepared before it is tinctured. Fresh herb should be minced finely to destroy as many cell walls as possible. Because fresh herbs contain variable amounts of water, they should be tinctured in the higher percentages of alcohol. Fresh roots should be sliced thinly or chopped finely. Some are very tough and require pruning shears for cutting (use of a meat cleaver is effective, but root pieces fly all over the place). Roots are best used fresh in the home pharmacy because when dried, they become too hard to be chopped without commercial equipment. Dried herb aerial parts are simply crushed, ground in a food mill or coffee grinder, or pressed through a screen before tincturing. Dried herbs swell with water when the menstruum is added, so room must be left in the macerating jar to account for this. The herb is usually “moistened” overnight before the menstruum is poured, to minimize any change in volume. If seeds are used, they should be dried for a few hours and separated from any chaff, then ground or bruised before tincturing.


The blender method is very effective—put menstruum and chopped herb into a blender, and begin blending. Keep adding pieces of herb until the blender can take no more. This method produces a stronger tincture, but it is more difficult to squeeze the menstruum from at completion of the tincturing process.


In the industry, two main methods are used to make TRs and FEs: percolation and maceration.






Glycerin Extracts, Glycerites, and Glycetracts


Glycetracts use glycerin and water as solvents. They were traditionally made with mucilaginous herbs like marshmallow (Althea officinalis) and licorice (Glycyrrhiza glabra), but now many herbs are available in this form. The following is true of glycetracts:







Fresh plant extracts are best used with glycerin because it is better at preserving fresh plant juice as opposed to extracting components from the plant cells. Glycerin extracts tannins well and may help protect them from precipitation in mixed alcohol tinctures. One limitation to using glycerin tinctures is the potential for microbial contamination, especially from fresh plant starting material. Glycetracts can be made through maceration or percolation, as described; however, glycerin is not as good a solvent as water or alcohol. This problem is overcome by the making of modern glycetracts by replacement.






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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on 14: Herb Manufacture, Pharmacy, and Dosing

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