Pharmacognosy

University of Perpetual Help System-Dalta College of Pharmacy Pharmacognosy Lab

Pharmacognosy is defined as an applied science which deals with the biological, biochemical and economic features of natural drugs and their constituents. It embraces knowledge of the history, distribution, cultivation, collection, selection, preparation, commerce, identification, preservation and use of drugs having their origin in the plants and animal kingdom. Brief History of Pharmacognosy In the early days, all information pertaining to drugs and their usage in Western culture was designated materia medica (means medical matter). The most famous commentary on drugs was written by Pedanios Dioscorides entitled De Materia Medica libri cinque (Concerning Medical Matter) which covered some 600 plant drugs plus a number of animal and mineral products. As the knowledge about drugs increased, specialized disciplines became a necessity. In early 19 th century, materia medica began to undergo division into pharmacology (the actions of drugs) and pharmacognosy (all aspects of drugs with lesser emphasis on actions). The word Pharmacognosyis from two Greek words pharmakon (drug) and gnosis (knowledge). This name was first thought to have been introduced by Christianus Anotheus Seydler, a medical student in Germany, who used the title Analectica Pharmacognistica in his dissertation in 1815. However, recent historical research has found that the name was earlier used by Johann Adam Schmidt in his Lehrbuch der Materia Medica which was published in Vienna in 1811. It described the study of medicinal plants and their properties. Plants have become the major source of medicinal and pharmaceutical substances. At present, people are going back to traditional medicine for the treatment and prevention of diseases. Plant chemistry or phytochemistry is an important element of pharmacognosy, different plant constituents have their own distinct pharmacological actions. Definition of terms Materia Medica means medicinal materials. It is synonymous with the substances and products derived from natural sources and employed by the physicians in the old days. Drugs are substances whether natural or synthetic, having therapeutic or medicinal properties, and chiefly used as medicines or an ingredient in medicine.

University of Perpetual Help System-Dalta College of Pharmacy Pharmacognosy Lab

Crude drugs are whole plants and animals and anatomical parts thereof which have not undergone any process or treatment other than what is essential to their proper packaging and storage. These are vegetable or animal drugs which consist of natural substances that have undergone no other process than collection and crying. Drug constituents are chief constituents and their derivatives obtained from drugs of biological origin or prepared synthetically or semisynthetically. Derivatives or Extractives are substances or mixture of substances present in crude drugs which are separated by various means and are employed in a more specific manner. Natural products are any of the following: Plant juices, exudates, secretions and extracts. e.g. aloe, acacia, orange oil, etc. Animal secretions and extracts. e.g. chymotrypsin, gelatin Microbial extracts and products. e.g. xanthan gum, sutilains Biologics are (a) products composed of antigenic matter or antibody preparations capable of developing a state of immunity in the patient. e.g. smallpox vaccine (b) diagnostic aids. e.g. tuberculin (c) related to human blood. e.g. platelets, whole blood. To evaluate a drug means to identify it and to determine its quality, purity and pharmacological value. The evaluation of a drug involves a number of methods which may be classified as follows: 1. Organoleptic evaluation makes use of the five senses. The appearance, feel (texture), smell (odor), taste and sound of materials are noted. This evaluative tool is used for natural product and crude drugs.

2. Microscopic evaluation makes use of the microscopic details of the plant part such as leaves, stem and roots. Powdered materials are also subjected to microscopic evaluation. Quality and size of particles are important in the determination and differentiation of starches. 3. Physical evaluation makes use of physical constants for the identification of the natural product. For instance, the identity and purity of a fixed oil can be determined through its specific gravity as a

University of Perpetual Help System-Dalta College of Pharmacy Pharmacognosy Lab

different substance will give a different SG and impurities will tend to change the SG of the oil. other physical parameters are melting point, boiling point, refractive index, etc. 4. Instrumental evaluation is a more refined investigation of a natural product. Infrared spectroscopy for example can reveal functional groups that are present in the natural product, establishing its identity and purity. Chromatography and spectroscopy are the most commonly used methods for this evaluation. 5. Chemical evaluation uses test reagents for establishing the identity of a natural product. Specific plant constituents will give specific color reactions with test

6. reagents. These reactions may even differentiate the same class of plant constituents. 7. Biological evaluation determines the effectiveness of the plant constituent. Test animals are employed to establish its safety and efficacy. MICROSCOPIC ANALYSIS – microscopic characteristics and histological cross-sections are important. Microscopes are used to observe hairs, vessels, esclereids, stoma and acellular-like crystals and grains of starch. This is used when macroscopic evaluation is not enough to differentiate drug products. (e.g. Histology for fresh samples, particle evaluation for powdered samples, etc.)

PHYSICAL ANALYSIS – important in the establishment of standards for identification and quality of the drug product. Physical parameters depend on the drug sample used (crude or natural product).        

Humidity Ash content/acid insoluble ash content Density Refractive index/optical rotation Foam index Solubility Melting point/boiling point Other tests

CHEMICAL ANALYSIS 

Phytochemical screening

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Minerals and constituents

other

University of Perpetual Help System-Dalta College of Pharmacy Pharmacognosy Lab

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Confirmation tests

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Other special tests - Acid value, saponification value

INSTRUMENTAL METHODS

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Chromatographic IR NMR

BIOLOGICAL  Toxicological test  Pharmacological tests - In vitro - In vivo

EVALUATION OF PLANTS AND DRUGS Plants are said to be indigenous if they grow in their native countries. Plants that are only introduced and are grown in a foreign land is said to be naturalized. Plant materials may be collected from the wild or may be cultivated. Cultivated plant materials have a greater advantage in that the growing conditions are controlled. Optimum temperature, water supply and soil nutrients ensure high quality of plant materials whereas the harsh conditions in the wild may affect the quality and amount of plant constituents. Here are the steps in the preparation of crude drugs for commercial use: Collection. The proper time of harvesting and collection is important because the quality and quantity of plant constituents vary depending on the time of day and season of the year. Usually the most active plant constituents are from mature plant parts and not the overly mature parts. Harvesting. The means of harvesting the plant part ensures is of also of prime importance. Mass harvesting may be done by mechanical devices but manual collection is always favored if the plant part is delicate. Drying. The removal of moisture from the plant material will prevent the growth of microbes such as molds and stops the action of enzymes that may degrade the plant constituent of interest. The following are drying techniques that may be employed. Natural drying methods include exposing the plant part under the sun or simply hanged to dry (air-dried). This poses advantage in that the heat-labile materials are not destroyed by the drying process. However, molds may grow because of longer drying time. Very plump plant parts are not recommended for this type of drying as it will take more time. Artificial drying methods include drying with the use of heaters or the most common would be the oven. Care must be observed so that the plant material is charred. Hence, temperature must be controlled. Garbling. This is the final step in the preparation of a crude drug. It is the removal of extraneous matter such as dirt or other plant parts that may have been collected with the plant part.

Packaging, storage and preservation. Appropriate containers for packaging, storage conditions such as humidity and temperature will ensure the preservation of the plant part.

ASH DETERMINATION The ash content of a crude drug is generally taken to be the residue remaining after incineration. The organic components of a crude drug are combustible. Thus, the ash represents the inorganic salts naturally occurring in the drug and adhering to it. These inorganic substances have little value for purposes for evaluation. It may also contain the inorganic matter as fraudulent adulterants to increase the weight of the crude drug. Different materials would have different ash contents, thus a change in the ash content of a crude drug may establish its identity and purity. The ash or residue remaining after incineration of organic compound is a measure of the amount of inorganic matter present as impurity. Addition of hot water is employed for the removal of more polar components. Alcohol may also be added and ignited. Usually what is left in the total ash are mainly carbonates, phosphates, silicates and silica. The total ash is the residue remaining after incineration. The acid insoluble ash is the part of the total ash which is insoluble in diluted hydrochloric acid. MOISTURE CONTENT Excessive water contained in drugs (e.g. aloes, gelatin, gums) are very uneconomical, and possibly may also activate enzymes with a suitable temperature, causing the proliferation of unwanted living organisms. Most vegetable drugs contain all essential food requirements for molds, insects, and mites to cause deterioration rapidly once infected or infiltrated. Loss on drying Loss on drying is employed by the USP and BP/EP principally due to small amounts of other volatile materials that contribute to the weight of a crude drug or sample. These materials qualify as volatile in temperatures of 100-105°C, and the sample is dried until it reaches constant weight. Special considerations are applied upon materials which require volatile substances such as balsams. PHYTOCHEMICALS Plants produce a vast number of substances of varying chemical structures. These constituents may be present all throughout the plant tissue but may

also be stored in certain plant parts. There are two main groups of plant constituents (phytochemicals) Primary metabolites- these are relatively abundant in plants but are of lower value. These include carbohydrates, proteins and lipids.

Secondary metabolites- these are constituents that are present in smaller quantities but possess higher pharmaceutical and pharmacological value compared to primary metabolites. These plant metabolites are also unique to particular species of plants. Secondary metabolites include alkaloids, steroids, tannins, flavonoids and others. These plant constituents may function for plant reproduction (as pollinator attractants) or protection (as antifeedants/poison). These plant constituents may be present in varying degrees in a single plant which may hinder the efficient extraction of the plant constituent of interest. Furthermore, they have exhibit different polarities, thus extracting solvents vary depending on the plant constituent to be isolated. PHYTOCHEMICAL SCREENING Phytochemical screening is a tool used by phytochemists or natural product chemists to evaluate the type of constituents present in plant samples. The methods used for screening should have the following characteristics: Simple Rapid Designed for minimum use of equipment Reasonably selective for the class of compounds under study Should provide additional information aside from the absence or presence of the plant constituent under study. Phytochemical screening is conducted on the crude ethanolic (for nonpolar constituents) and aqueous (for polar constituents) extracts to determine the presence of active principles in the plant material. This gives the researcher a hint as to how the plant material is to be prepared, which extracting solvent is to be used and what isolation technique is to be performed. Other problems that are likely to be encounterd are:

Difficulty to determine the presence of a particular class of compounds due to a large number of diverse compounds occurring in the plant. Uncertainty as to whether a substance is originally present in the plant or simply a decomposition product due to the action of the light, heat, acid, alkali or enzyme. Varying composition of the plant part is not the same in all circumstances.

KINDLY STUDY THE PHYTOCHEMICAL SCREENING TESTS:  Phytochemical constituent and their specific tests  Reagents used  Visual positive result (color, specific constituent present)