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1. CLASSIFICATION OF NATURAL DRUGS
Introduction The term crude drug generally applies to the products from plant and animal origin found in a raw form. The crude drugs are classified as organised and unorganised drugs. Organised drugs are the parts of plants, which are made of cells. Unorganised drugs are group of solid and liquid, which do not consists of parts of the plants and are obtained from natural sources by various extraction procedures. In Pharmacognosy, the crude drugs may be classified according to the following system of classification:
- Alphabetical classification
- Taxonomical classification
- Morphological classification
- Chemical classification
- Pharmacological classification
- Chemotaxonomical classification
- Serotaxonomical classification Alphabetical classification Crude drugs are arranged in alphabetical order. Most of the reference book and pharmacopoeia’s are arranged according to the Latin or the English name. e.g. Indian Pharmacopoeia British Pharmacopoeia British Pharmacopoeia codex British Herbal Pharmacopoeia United States Pharmacopoeia National Formulary Encyclopaedia of common natural drugs However, this type of classification does not provide any information about the scientific nature of the drug and does not indicate whether they are organised or unorganised. Merits _ It is easy and quick to use. _ There is no repetition of entries and is devoid of confusion. _ In this system location, tracing and addition of drug entries is easy.
Demerits There is no relationship between previous and successive drug entries. Taxonomical classification Taxonomical classification is purely a botanical classification and is based on principles of natural relationship and evolutionary developments. They are grouped in kingdom, phylum, class, order, family, genus and species. e.g. (i) (ii) Phylum : Spermatophyta Phylum : Spermatophyta Division : Angiospermae Division : Angiospermae Class : Dicotyledons Class : Dicotyledons Sub-class : Sympetalae Order : Rosales Order : Tubiflorae Family : Leguminosae Family : Solanaceae Sub- Family : Papillionaceae Genus : Atropa, Datura Genus : Astragalus, Glycyrrhiza Species : Atropa belladonna, Species : Astragalus gummifer , Datura stramonium Glycyrrhiza glabra Merits Taxonomical classification is helpful for studying evolutionary developments. Demerits This system also does not co-relate in between the chemical constituents and biological activity of the drugs and not recognise the organised or unorganised nature of crude drugs. Morphological classification In this system, the drugs are arranged according to the morphological or external characters of the plant or animal represented into organised and organised. The organised drugs include parts of plants like leaves, flowers, fruits, woods, barks, rhizomes. The unorganised drugs are dried latex, extracts, resins, gums etc. Examples are as follows, Seeds : Nux vomica, Isapgol, Linseed, Nut meg, Castor Leaves : Senna, Digitalis, Eucalyptus, Vasaka, Neem Barks : Cinnamon, Cinchona, Cassia, Kurchi, Arjuna Woods : Quassia, Sandal wood
Merits It is a popular approach for phytochemical studies. In this classification, it is possible to establish relationship between drugs of the same chemical nature Demerits Ambiguities arise when particular drugs possess a number of compounds belonging to different groups of compounds . Pharmacological classification Grouping of drug according to their pharmacological action of their active constituent or their therapeutic use is termed as pharmacological or therapeutic classification of drug. Drugs like digitalis, squill and strophanthus having cardiotonic action are grouped together irrespective of their parts used or phylogenetic relationship or the nature of phytoconstituents they contain. Anticancer - Vinca, Podophyllum, Taxus Anti-inflammatory - Colchicum, Turmeric Antiamoebic - Ipecacuanha, Kurchi Antiasthmatic - Ephedra, Lobelia Anthelminthic - Quassia, Male Fern Antispasmodic - Datura, Hyoscyamus, Astringent - Black Catechu, Myrobalan Analgesic - Opium Antidiabetics - Gymnema, Pterocarpus, Methi Antimalarial - Cinchona, Artemisia Carminatives - Coriander, fennel, clove Purgatives - Senna, Rhubarb Expectorant - Tulsi, Vasaka Cardiotonic - Digitalis, Squill, Strophanthus Local anaesthetics - Coca Merits This system of classification can be used for suggesting substitutes of drugs, if they are not available at a particular place or point of time. Demerits
Drugs having different action on the body get classified separately in more than one group that causes ambiguity and confusion. Cinchona is antimalarial drug because of presence of quinine but can be put under the group of drug affecting heart because of antiarrhythmic action of quinidine. Chemotaxonomical classification Chemotaxonomy has correlated the relationship between plant taxonomy and chemical constituents. It gives close relationship between chemical constituents of plants and their taxonomical status. Some examples are Tropane alkaloids : Solanaceae ( About 20 genera of Solanaceae family have tropane alkaloids). (Belladonna, Datura, Hyoscyamus). Indole alkaloids : Apocynaceae (Vinblastin, Ergotamine) Volatile oils : Umbelliferae (Fennel, Coriander, Dill); Rutaceae (Citrus fruits) Serotaxonomical classification The study of antigen-antibody reaction is called serology. The application or utility of serology in solving taxonomic problems is called Serotaxonomy. The substance capable of stimulating the formation of an antibody is called antigen. A highly specific protein molecules produced by plasma cells in the immune system is called antibody. The antibodies combine chemically with specific antigens. Serotaxonomy means classification of very similar plants by means of differences in the proteins they contain. It determines the degree of similarity between species, genera, family etc. by comparing the reaction with antigens from various plant taxa with antibodies present against a given taxon. This technique also helps in the comparison of single proteins from different plant taxa.
5. Presence of organic matter obtained from the same plant: The other parts of the same plant are added to the genuine drugs: e.g. Clove is mixed with clove stalk, caraway fruit is mixed with other part of inflorescence.
- Substitution by addition of worthless or heavy materials: Pieces of lime stone mixed with Ferula asafoetida (Asafoetida), lead shot mixed with pieces of Papaver somniferum (opium).
- Addition of synthetic principles : It is the use of synthetic chemicals to enhance the natural character. Addition of benzyl benzoate to peru balsam, citral to citrus oils and lemon oil to orange oil are examples. DRUG EVALUATION Drug evaluation ensures the identity and determination of purity and quality of drugs. The evaluation of a drug is done by studying its various properties. The various properties are organoleptic property, microscopic property, biological property, chemical property and physical property. Organoleptic Evaluation : Organoleptic evaluation of crude drugs refers to the evaluation of a drug by colour, odour, taste, size and shape, occasionally the sound or snap of fracture and special features including touch, texture, etc. Evaluation is carried with the help of sensory organs. The adulteration of caraway with Indian dill, Alexandrian Senna with dog senna or palthe senna, can be identified by morphological (organoleptic) techniques. Microscopical Evaluation : This method allows more detailed examination of drug, and it can be used to identify the organized drug by their known histological character. Microscope can also be used for a quantitative evaluation of drugs and adulterated powders. This is done by counting a specific histological feature such as, Stomatal Number Stomatal Index Vein-islet Number Palisade Ratio Quantitative Microscopy Refractive Index Stomatal number: It is average no. of stomata per sq. mm of the epidermis of the leaf. It is effected by various factor like age of plant, size of leaf, environmental condition etc.
Determination of Stomatal Number - Place leaf fragments of about 5x5 mm in size in a test tube containing about 5 ml of chloral hydrate solution and heat in a boiling water-bath for about 15 minutes or until the fragments become transparent. Examine with a 40 x objective and a 6x eye piece, to which a microscopical drawing apparatus is attached. Mark on the drawing paper a cross (x) for each stomata and calculate the average number of stomata per square millimeter for each surface of the leaf. Species Stomatal number Upper epidermis Lower epidermis Atropa belladonna 7.5 to 10 to 17.5 77.5 to 113 to 176 Datura stramonium 59 to 87 to 140 145 to 200 to 254 Cassia angustifolia 180 to 200 to 223 195 to 220 to 257 Stomatal index: The stomatal index is the percentage of the number of stomata formed to the total number of epidermal cells, including the stomata, each stoma being counted as one cell. Stomatal index = S× E+S Where S = the number of stomata in a given area of leaf; and E = the number of epidermal cells (including trichomes) in the same area of leaf. Species Stomatal Index Upper surface Lower surface Atropa belladonna 2.3 to 10.5 20.2 to 23 Digitalis purpurea 1.6 to 4.0 19.2 to 25. Vein-Islet number: The mesophyll of a leaf is divided into small portions of photosynthetic tissue by anastomosis of the veins and veinlets; such small portions or areas are termed “Vein- Islets”. The number of vein-islets per square millimeter of leaf surface is termed as the Vein-Islet number. This value has been shown to be constant for any given species and proved useful for the critical distinction of certain nearly related species. Species Vein islet number Cassia angustifolia 19 to 23 Digitalis purpurea 2 to 5.
to a constant weight and calculating the loss of weight. e.g. Aloes – not more than 10% w/w Viscosity : Viscosity of a liquid is constant at a given temperature and is an index of its composition. Hence, it is used as a means of standardizing liquid drugs. e.g. Liquid paraffin – not less than 64 centistokes. Melting Point: In case of pure phytochemical, melting points are very sharp and constant. The crude drugs from plant or animal origin, containing the mixed chemicals, are described with certain range of melting point. e.g. Colophony-75-85˚C, Cocoa butter- 30-33˚C. Optical Rotation: Optically active compounds have the property of rotating the plane of polarized light in pure state towards right (dextrorotatary) or left (levorotatary) known as optical rotation. Normally, the optical rotation is determined at 25˚C using sodium lamp as the source of light. e.g. castor oil has optical rotation from +3.5˚to +6˚. Refractive Index: When a ray of light passes from one medium to another medium of different density, it is bent from its original path. Thus, the ratio of velocity of light in vaccum to its velocity in the substance is said to be the refractive index of the second medium. It is measured by means of refractometer. It is constant for a pure drug and varied with wavelength of incident light, temperature and pressure e.g. Castor oil has refractive index 1.4758-1. Viscosity : Viscosity of a liquid is constant at a given temperature and is an index of its composition. Hence, it can be used as a means of standardizing liquid drugs. Solubilty: The presence of adulterant could be indicated by solubility studies e.g. Pure Asafoetida is soluble in carbon disulphide. Ash Content: The residue remaining after incineration is the ash content of the drug, which simply represents inorganic salts naturally occurring in drug or adhering to it or deliberately added to it as form of adulteration. When drug is incinerated, the organic matter is burnt away and an inorganic residue is left which is designated as ash. Analysis of plant ash shows that it contains the oxides of Ca, Mg, K, Na, Si, P and Fe as well as minute quantities of other elements as boron. The ash determinations are useful for detecting low-grade products, exhausted drugs and excess of sandy or earthy matter
especially in powdered drugs. Total ash usually consists of carbonates, phosphates, silicates and silica. Acid insoluble ash is a part of total ash insoluble in dilute HCl. The ash remaining following ignition of medicinal plant material is determined by three different method which measure total ash, acid insoluble ash, water soluble ash. Total ash: Total ash method is used to measure the total amount of material remaining after incineration. Total ash is useful to detect the drugs which have been coated with chalk, lime or calcium sulphate to improve their appearance e.g. Ginger. And presence of excessive extraneous mineral matters introduced in the processes or collection; drying and powdering Incinerate about 2 to 3 g accurately weighed, of the ground drug in a tared platinum or silica dish at a temperature not exceeding 450º until free from carbon, cool and weigh. If a carbon free ash cannot be obtained in this way, exhaust the charred mass with hot water, collect the residue on an ashless filter paper, incinerate the residue and filter paper, add the filtrate, evaporate to dryness, and ignite at a temperature not exceeding 450º. Calculate the percentage of ash with reference to the air-dried drug. Acid insoluble ash: Acid insoluble ash is the residue obtained after boiling the total ash with dil. HCl and igniting the remaining insoluble matter. It measured the amount of silica present, especially as sand siliceous earth Detects the presence of heavy metals in earthy matter in drugs since the calcium oxide, carbonate & silicates resulted by the incineration & are soluble in dilute hydrochloric acid. Procedure: Boil the ash obtained for 5 minutes with 25 ml of dilute hydrochloric acid; collect the insoluble matter in a Gooch crucible, or on an ashless filter paper, wash with hot water and ignite to constant weight. Calculate the percentage of acid-insoluble ash with reference to the air dried drug. Water soluble ash: is the difference in weight between total ash and residue after treatment of total ash with water. Boil the ash for 5 minutes with 25 ml of water; collect insoluble matter in a Gooch crucible, or on an ashless filter paper, wash with hot water, and ignite for 15 minutes at a temprature not exceeding 450º. Substract the weight of the insoluble matter from the weight of the ash; the difference in weight represents the water soluble ash. Calculate the percentage of water-soluble ash with reference to the air dried drug.
LOSS ON DRYING : Loss on drying is the loss of mass expressed as w/w and can be determined by following procedure : Place about 10 g of drug (without preliminary drying) after accurately weighing (accurately weighed to within 0.01 g) it in a tared evaporating dish at 105º for 5 hours, and weigh. Continue the drying and weighing at one hour interval until difference between two successive weighing corresponds to not more than 0.25 per cent. Constant weight is reached when two consecutive weighings after drying for 30 minutes and cooling for 30 minutes in a desiccator, show not more than 0.01 g difference. HAEMOLYTIC ACTIVITY : Haemolytic activity of plant material is determined by comparison with that of reference material, Saponin R, having haemolytic activity of 1000 units/g. Method of preparation of standard: Fill a glass stopper flask to 1/10 of its volume with sodium citrate. Add sufficient volume of blood freshly collected from healthy ox and shake, this can be stored for about 8 days at 2-4̊ c. place 1ml of citrated blood in a volumetric flask with phosphate buffer pH 7.4. Haemolytic activity = 1000× a b Where, 1000 = defined haemolytic activity of Saponin standard a = quantity of saponin standard that produce total haemolysis(g) b = quantity of plant material that produce total haemolysis (g) BITTERNESS VALUE : Medicinal plants having strong bitter taste are therapeutically used as appetizing agents. The bitterness is determined by comparing the threshold bitter concentration of an extract material with that of quinine hydrochloride. The bitterness value is expressed as units equivalent to the bitterness of a solution containing 1 gm of quinine hydrochloride in 2000ml. 0.1 gm of quinine hydrochloride is dissolved in 100ml drinking water and the stock solution is prepared. Then it is diluted and tested and compared with drug. Bitterness value in unit per gm = 2000×C A×B Where, A = concentration of stock solution B = volume of test solution in tube with threshold bitter concentration C = quantity of quinine hydrochloride in the tube with threshold bitter concentration
Chemical Evaluation : Determination of the active constituent in a drug by chemical tests is referred to as chemical evaluation. Qualitative analysis Detection of alkaloids : The small portion of solvent free chloroform ,alcoholic and water extract are stirred separately with few drop of dilute HCl and filtered .the filterate may be tested carefully with various alkaloidal reagents such as: Reagents Observation Mayer reagents (pottasium mercuric iodide solution ) Cream precipitate Dragondroff’ reagent(pottasiun bismuth iodide solution) Redissh brown ppt. Wagner’s reagent (iodine pottasium iodide solution) Redissh brown ppt. Hager’s reagents Yellow ppt. Detection of carbohydrate and glycosides: Small quantity of alcoholic and aq. Extracts are dissolved seperately in 5 ml of distilled water and filtered. The filtrate may be subjected to molish test to detect presence of carbohydrate. · Another small portion of extract is hydrolysed with dilute sulphuric acid for few hours in water bath and subjected to liebermann- burchard,legals,and borntrager test to detect presence of different glycosides. Detection of saponins- About 1 ml of alcoholic and aq extract is diluted separately with distilled water to 20 ml and shaken in graduated cylinder for 15 minutes. one cm layer of foam indicates presence of saponins. The test solution may be subjected to test for haemolysis. Detection of protein and free amino acids: Small quantity of alcoholic and aqueous extract are dissolved in few ml of water and subjected to millon’s, biuret’s, and ninhydrin test. Detection of volatile oil: About 50 mg of powdered material is taken in a volatile oil estimation appartus and subjected to hydrodistilation. The disttilte is collected in graduated tube of assembly in which aq. Portion is automatically separated from the volatile oil, if it present in the drug and returned back to distillation flask. Microchemical tests:
