Challenges and scientific issues in the standardization of botanicals and their preparations. United States Pharmacopeia's dietary supplement verification program—A public health program

Abstract

The role of the United States Pharmacopeia (USP) in the regulation of dietary supplements, USP's dietary supplement verification program and the challenges and scientific issues in the standardization of botanicals and related products are discussed.

Introduction

United States Pharmacopeia is a standard setting non-government, and not-for-profit organization. USP establishes public standards for drugs, dietary supplements, biologics and other articles used in the health care industry, that are enforceable by the Food and Drug Administration under the Food, Drugs and Cosmetics Act. The passage of the Dietary Supplement Health and Education Act of 1994 (DSHEA 1994) is an acknowledgment of the American people's desire to explore the benefits of certain supplements in the prevention of disease conditions. The DSHEA defines a dietary supplement as one that contains one or more of the following ingredients: vitamin, mineral, an herb or other botanicals, an amino acid, a dietary substance for use by man to supplement the diet by increasing the total daily intake or a concentrate, metabolite, constituent, extract or combination of these ingredients. With the passage of the Dietary Supplement Health and Education Act of 1994, USP's involvement with the development of public standards for dietary supplements steadily increased and, in fact, the growth of the dietary supplements industry in the United States during the past decade has been phenomenal.

It is known that American Health care costs are rising at an alarming rate to astronomical figures. The American public has recently embraced the promises and potentials of dietary supplements wholeheartedly as can be seen by the growth of the supplement industry. According to the Nutrition Business Journal, in 2003 American consumers spent about $19.5 billion on nutritional products that includes $15.5 billion on vitamins, minerals, amino acids and other dietary supplements. Botanical products alone account for $4 billion. It must be noted that initially during the early 1990s, the market-driven growth of the business was in double digits, namely 17–20%. However, the market-driven enterprise is undergoing a fundamental change to a business of science based products that will be driven by the results of clinical research. This is reflected in the recent market growth projection by the Nutrition Business journal to 6–8%. Several news items and articles in leading national newspapers point to the fact several marketed products do not live up to their label claim. These stories have caused further confusion in the minds of the consumers. The questions in the minds of the consumers as revealed by the media are: How do we choose a supplement? Which brand should we choose? Will it contain what the label says? Will it be safe and will I get the benefit that is attributed to the supplement?

Recent surveys reported in news media appear to indicate that a large percentage of the American public would like to see products backed by science which means products supported by clinical research. This means consumers are increasingly demanding products of known quality. This is where the public standards enter into the picture. An open and democratic process involving the manufacturers, government agencies, academia, research institutions and other interested parties might be involved in establishing public standards. Such standards assure the consumers proper identity, safety and quality of the products.

In this article, a discussion is presented on issues that are taken into consideration by the Expert Committees of the United States Pharmacopeia which establishes public standards for drugs, dietary supplements, biologics and other articles used in the healing art, in the development of public standards for botanicals and their preparations. Pharmacopeial specifications are public standards. It is well known that the quality of raw material used in the manufacture of a product is reflected in the quality of the finished product. Thus traditionally when establishing public standards for drug products such as tablets and capsules, initially standards for the active bulk drug substance (the raw material) are established. In the case of botanical dosage forms, the “active” bulk substance is the botanical extract and therefore standards for the botanical extract need to be established prior to establishing standards for dosage forms. However, variations of season, soil conditions, quality of ground water used in irrigation etc., have a profound impact on the composition of the chemical constituents of raw plant materials. This therefore necessitates the establishment of quality parameters for the plant material part from which the extract is derived. Thus, the standardization of botanical products becomes a three-pronged approach:

$$\underset{\text{Stage}1}{\text{Plant}\text{material}}\to \underset{\text{Stage}2}{\text{Plant}\text{extract}}\to \underset{\text{Stage}3}{\text{Botanical}\text{dosage}\text{forms}}$$

Pharmacopeial monographs for botanicals raw material have the following sections and test requirements.

Definition: Pharmacopeial monograph on a botanical article has to be very specific in its definition by specifying the genus and species thereby indicating that the standards apply to that particular plant part of the stated genus and species. For example Ginkgo preparations are prepared from the leaves and hence the official monograph on Ginkgo defines it as consisting of the dried leaf of Ginkgo biloba belonging to the family Ginkgoaceae. In keeping with the customary practice of the U.S. Pharmacopeia to state, after the name of the species, the name of the botanist, Linnaeus, who first described the species (or the current commercially dominant description), is specified in the definition.

Packaging, storage and labeling: Pharmacopeial specifications are shelf-life specifications and therefore the type of container in which the article is to be stored as well as the temperature conditions of storage will be specified in the monograph. Under the stated conditions, the pharmacopeial articles are expected to retain their stated potency until the expiry date claimed on the product label.

The name in Latin binomial form is the only recourse at present to save the public from the prevailing hopeless situation in the market place where manufacturers and distributors of botanicals use several different names on the product thus causing confusion in the minds of the consumers. Thus, the product label of a pharmacopeial article is expected to specify, in addition to the common name, the name in Latin binomial form as given in the definition. The insistence of the name in Latin binomial form is both a regulatory issue and a consumer issue.

Identification: A pharmacopeial monograph specifies Identification tests to ensure confirmation that the identity of the article under examination is in agreement with what is stated in the definition of the article. Histology and morphology tests are usually complimented by other tests involving comparison with Authenticated Reference Plant Material (ARPM) utilizing modern analytical techniques such as thin-layer chromatography, liquid chromatography etc. ARPM of the desired species is used for comparison with the article under test to validate species identity and to confirm chemical identity through thin-layer chromatographic techniques. ARPM also helps in the detection of undesirable species in the material under test.

Pharmacopeial monographs would employ chemical methods of identifying the active ingredients or marker substances either as a class (e.g. alkaloids, terpenes) or by their functional group (e.g. ketones, phenolic hydroxyl) through thin-layer or liquid chromatographic techniques, color tests or instrumental methods of analysis involving spectrophotometric techniques such as UV and IR.

Microbial limits: It is well known that medicinal plant materials, products of nature, generally are contaminated with a great number of bacteria and molds arising from the soil. Further microbial contamination is also caused by harvesting, handling and processing practices. Analytical determination of E. coli and yeast and molds counts of raw plant material is usually an indication of the harvesting and post-harvesting handling practices. One would expect the botanical materials to be decontaminated with post-harvest methods (e.g. chemical treatment, gamma irradiation) at the source of export (e.g. in the field, customs shed). However, this does not assure that the material would arrive at the port of import free from any contamination. Pharmacopeial monographs specify absence of pathogens such as E. coli and Staphylococcus aureus in the articles of commerce. Taking into consideration the end use of the article, appropriate limits for total aerobic count, mold count and E. coli are also specified. Depending on the type of plant material, aflatoxins test requirements are specified.

Tests for other contaminants or impurities:

• Limit tests: Since botanicals are products of nature, soil contamination is almost a predictable feature. Tests for Total ash content, Water-soluble ash, Acid-insoluble ash etc. would address this contaminant.

• Heavy metals: This test ensures contamination of the plant material with harmful heavy metals such as lead are detected and limited to low levels. The primary source of this contamination, besides ground water, is milling operations.

• Pesticide residues: Botanicals that are labeled and marketed as dietary supplements are treated and regulated as foods in the United States of America. There is zero tolerance for pesticides in foods and this is applicable for botanicals as well. Where no limit is set, the limit is zero. In reality a wide variety of pesticides are used worldwide in the cultivation of botanicals and this necessitates testing botanicals for a list of pesticides depending on the country of origin in addition to those that are in use at the importing country.

Tests for marker substances:

Botanical raw material and their extracts usually contain complex mixtures of several chemical constituents. For a large majority of botanical plant material and their extracts used as dietary supplements, it is not known with certainty which of the various components is responsible for the reported pharmacological effect. It is generally believed that several constituents act synergistically to provide the reported effect. Constituents of herbal drugs can be classified into four categories as follows:

• Active principles—Constituents that belong here may have known clinical activity and thus are known by the name active principle(s).

• Active marker(s)—These constituents have some known pharmacological activity contributing to some extent efficacy. For example, alliin present in Garlic comes under this category. These constituents may or may not have clinically proven efficacy. A minimum content or range for active markers is usually specified in pharmacopeial monographs. A quantitative determination of active marker(s) during stability studies of botanical dosage forms provides necessary information in arriving at suitable expiration dates.

• Analytical markers—Where neither defined active principles nor active markers are known, certain constituents of the botanical raw material and their extracts are chosen as candidates for quantitative determination. These markers aid in the positive identification of the article under test. Further maintaining a minimum content or a specified range of the analytical markers helps to achieve standardization of the plant extract and to arrive at suitable expiration date during stability studies.

• Negative markers—Some constituents may have allergenic or toxic properties that render their presence in the botanical extract undesirable. A stringent limit for these negative markers may be specified in compendial articles.

An example of negative markers would be Ginkgolic acids in Ginkgo preparations. The highly sensitizing potential of Gingkolic acids which are alkyl phenols have been reported to be confirmed recently by skin tests in guinea pigs. Ginkgolic acids are structurally similar to the highly allergenic urushiols observed from the plants belonging to the family Anacardiaceae and thus stringent limits for these are called for in plant extracts that may contain them.

Standardization of botanical extracts: The next critical issue is the standardization of botanical extracts and other dosage forms. Extracts may be defined as concentrated preparations with liquid, solid or intermediate consistency. In the pharmaceutical extraction practice for articles of botanical origin, the constituents of interest are completely or partially separated from the interfering components with the aid of alcohol, alcohol–water mixtures or other suitable solvents. This extraction process involves the removal of the desired constituents from the plant material with suitable solvent or solvent mixtures, the evaporation of all or nearly all of the solvent and the adjustment of the residual fluids, masses, or powders with the aid of suitable inert materials to the prescribed standards. At the end of extraction, unwanted material is removed. The principal methods of extraction are percolation, maceration, digestion, infusion and decoction.

The products obtained by extraction are fluid extracts, powdered extracts, semi-solid extracts, and tinctures. Extracts by definition are enriched in the constituents of interest. It is reported that more than 80% of herbal medicinal products commercialized in Germany and other countries contain extracts mainly in the form of dry extracts. The key issues in the manufacture of extracts are: (1) the ratio between crude herbal drug and the solvent or solvent mixture used, (2) the type and concentration of the solvent, (3) the extraction method and (4) purification steps. Greater emphasis is placed on the ratio between the crude plat material and the extract obtained as the varying ratio might lead to differences in the composition. A standardized and validated process of extraction alone can assure an extract of consistent quality. Standardized extracts are usually tested for a minimum content or range of certain specified marker compounds.

Pharmacopeial specifications for extracts used in dosage forms include the following: (1) container label to indicate the name of the plant part used, name of the solvent or solvent mixture used, ratio of the starting material to final product, name of any preservative used and name of diluents used; (2) heavy metals limits—20 ppm; (3) alcohol content (90–110% of the labeled amount); (4) pesticide residues, organic volatile impurities, residual solvents are controlled.

The issues involved in the botanical dosage forms: Botanical preparations are formulated into the same dosage forms as vitamins, minerals, and drugs using the same formulation science and manufacturing technology. Therefore, issues involved in the standardization of botanicals dosage forms are not different from those of drugs. For example for oral solid dosage forms such as tablets and capsules, performance characteristics is an important parameter. The important performance characteristics for oral solid dosage forms are:

Uniformity of dosage units, Content uniformity versus Weight variation, Disintegration versus (in vitro) Dissolution. Although predictable biological effects and dosing intervals have yet to be determined through systematic and acceptable clinical trials for the majority of marketed botanical dosage forms, it can be argued that a dissolution testing is an integral part of the public standard for these preparations. A dissolution requirement is expected to provide assurance that the dosage form is formulated and manufactured appropriately in order to ensure that the index or marker ingredients will dissolve in the gastrointestinal tract and be available for absorption. Here no assumption is made that the index or marker compound selected for demonstration of dissolution is responsible for the purported effect. A dissolution testing is valuable in that it assures that the formulation process used is reflective of the state-of-the-art technology currently available, and also provides a lot-to-lot performance over a product's shelf-life. It provides an assurance that the excipients used in the dosage form to facilitate transfer of the botanical index or marker compound to the human system are appropriate.

A Content uniformity requirement in an acknowledgement of the existence of dose–response curve and the attendant dosing intervals. Where the dose–response curve is either minimal or non-existent, perhaps uniformity of dosage units can be best assured by Weight variation requirement. In this test, 20 or 30 units are weighed individually and no two units differ in weight by more than 5%.

Quality control/Regulatory aspects of dietary supplements: Under the DSHEA 1994, dietary supplements label shall bear the statement that the product is a dietary supplement and are allowed to make structure–function claim. No medical claim is allowed on product labels. There is controversy over what is a medical claim. Very often, we find product labels containing statements that are almost medical claims. Some of the statements that we notice on labels are often misleading. A dietary supplement product label which makes a structure–function claim relating to arthritis such as maintains healthy joints also bears a statement “as featured in the book Arthritis cure.” It is important to understand what is structure–function claim and how it differs from drug or medical claim. This can be illustrated this with a dietary supplement such as St. John's wort Tablets. A structure–function claim would be “helps to maintain healthy mood” or “maintains healthy mood.” If the label states that it treats depression, that would be a medical claim. A drug by definition treats, mitigates or cures a disease condition. A dietary supplement is intended for prevention of certain conditions.