Introduction to Pharmacognosy | Crude drugs | Natural products

Pharmacognosy is a science which deals with the study of crude medicine in substances obtained from natural sources mainly plant and animal. Crude medicine; are drugs which are from plant or animal not processed (no any addition to add potency). The word "Pharmacognosy" derived from the Greek words "Pharmakon” –a drug, or medicine “gignosis” –to acquire knowledge of

Pharmacognosy is a science which deals with the study of crude medicine in substances obtained from natural sources mainly plant and animal


It deals with scientific study of structural, physical, chemical and sensory characters of crude drug obtained from plant, animal and mineral sources.

Therefore: Pharmacognosy is “an applied science that deals with the biological, biochemical and economic features of natural crude drugs and their active constituents (derivatives)”.

Pharmacognosy is closely related to botany and plant chemistry. From botanical side, it is concerned with the description and identification of drugs, both in whole state and in powder and with their history, commerce, collection, preparation and storage, which are of fundamental importance particularly for pharmacopoeial identification and quality control purposes.

Pharmacognosy does not include the study of synthetic drugs. Pharmacognosy is NOT identical to Medicinal Chemistry and/or Pharmacology but utilizes their methods. Studies drugs from plants, animals and minerals. E.g.: Digitalis leaf and its glycosides (digitoxin), Rauwolfia root and its alklaoids (reserpine). Thyroid gland and its extracted hormone (thyroxin)

Pharmacognosy is not confined to plants but also investigates biodynamic compounds in animals, marine organisms, fungi, and micro-organisms. Natural drug constituents which have been prepared synthetically (e.g. ephedrine, vanillin, caffeine, codeine, menthol, penicillin) and synthetic substances are considered a definite part of pharmacognosy.

Definitions

Pharmacognosy “derived from the Greek Pharmacon, a drug, and Gignosis which means acquire knowledge. Pharmacognosy  is  the  study  of  crude  drugs  obtained  from  plants,  animals  and  mineral kingdom

Crude drugs: Are those natural products such as plants or part of plants, extracts and exudates which are not pure compounds and used in medicine

Monographs on a large number of crude drugs, give written descriptions, tests of identity, purity and assays of active constituents.

Pharmacology: This dealt with drug actions and effects.

Medicinal chemistry: the science of synthetic drugs.

Ethnobotany is the study of the relationship between people and plants, field includes studying plants as medicines, alternative methods for healing, as wild foods, as agricultural crops; modes of transportation; as clothing and in the religious ceremonies.

Ethnopharmacology is the scientific study correlating ethnic groups, their health, and how it relates to their physical habits and methodology in creating and using medicine.

Traditional medicine: It is the sum total of all non-mainstream medical practices, usually excluding so called “western” medicine

Crude drugs

Crude drugs are drugs that consist of natural substances that have undergone only the processes of collection and drying. Natural substances refer to those substances found in nature (from natural sources); Whole plants or organs of plants, e.g. leaves, flowers, seeds, and barks, or vegetable saps, extracts and secretions. Whole animals; glands or other animal organs, extracts, secretions; that have not had changes made in their molecular structure (as found in nature)

Also, means any product that has not been advanced in value or improved in condition by grinding, chipping, crushing, distilling, evaporating, extracting, artificial mixing with other substance or by any other process or treatment beyond what is essential to its proper packing and the prevention of decay or deterioration pending manufacture. Today, Crude drugs are rarely used as therapeutic agents; more often their chief principles (derivatives or extractives which contains active constituents) are separated by various means.

Natural products

A natural product is a substance obtained from a natural source.

1. A crude drug, e.g. Senna, Cascara, Cinchona, etc.

2. A galenical preparation of a crude drug, e.g. extracts and tinctures, etc.

3. A pure compound, e.g. morphine, atropine, digoxin, etc.

4. A semithynthetic product, e.g. etoposide, teniposide, hyoscine butyl bromide etc.

Use of Natural Products

1. As drugs for the treatment of a wide range of diseases, e.g. morphine, atropine, digoxin, hormones, antibiotics, etc.

2. As pharmaceutical aids in pharmaceutical industry e.g. suspending and emulsifying agents, suppository bases, binders, sweetening and colouring agents, etc.

3. In cosmetics as flavouring and colouring agents, etc.

4. In culture media for the propagation of micro-organisms in microbiology laboratories and biotechnology.

5. General uses e.g. in food industries: as dusting powders, as indicators and in perfumery.

Classification of Medicinal Plants

A- Alphabetical Classification

Either Latin or Vernacular names may be used. Although simple and suitable for quick   references, these names give no indication of interrelationships between drugs e.g. in Pharmacopoeias.

B- Taxonomic Classification

Based on botanical classification, drugs are arranged according to the plants from which they are obtained into: Classes, orders, families, genera and species.

C- Morphological Classification

Drugs are divided into groups

Organized drugs: Leaves, flowers, fruits, seeds, wood, barks, rhizomes and roots etc.

Unorganized drugs: Dried lattices, extracts, gums, resins, oils, fats and waxes

D- Pharmacological or therapeutic Classification

This involves the grouping of drugs according to the pharmacological action of their most important constituents or their therapeutic uses, e.g. cardiotonic drugs, CNS stimulants etc.

E- Chemical or Biogenetic Classification

According to the important constituents e.g. alkaloids, glycosides, volatile oils, etc. or based on their biosynthetic pathways. Used when the teaching of pharmacognosy is phytochemically biased.

Importance of some medicinal plants

Quinine

Historically, malaria has been one of the worst of all human diseases. In some countries malaria is common and millions of people suffer from the disease throughout the world. Malaria is caused by a sporozoan of the genus Plasmodium and is passed from one human to another by mosquitoes.

In the 17th century, Jesuits in South America discovered that a native remedy for other diseases made from an infusion of the bark of cinchona (Cinchona spp., Rubiaceae) coincidentally controlled malaria.

The Dutch acquired seeds from a high-yielding plant near Lake Titicaca, Bolivia. After several years of trying to grow the plants and improve them, they were able to begin to cultivate high quality lines in the Dutch East Indies and eventually they got a monopoly on the production of quinine.

At the time of W.W. II, the allies were cut off from a supply of quinine. During the war, a number of synthetic substitutes for quinine were developed. Many are still important, but resistance to most is a major problem

Quinine is also used in small amounts to make tonic water and other soft drinks such as bitter lemon. Although there have been extensive searches for new plant-derived antimalarials, few have surfaced. One, artemisinin from Artemisia annua, has proven effective and is currently being used in Southeast Asia.

Ephedra or ma huang, Ephedra spp., Ephedraceae

Infusions of Ephedra spp. (Ephedraceae, a gymnosperm) have been used for thousands of years in China. There it is often called "ma huang". In the 1920's the plant was "discovered" by western medicine and the active compounds isolated. Ephedrine and a series of related compounds are used today as decongestants (e.g., in Sudafed, Robitussin etc.) and to treat low blood pressure. Most of the active compounds are made synthetically, however.

Willows and aspirin

Even in the time of Dioscorides it was known that extracts of willow bark (Salix spp., Salicaceae) and leaves alleviated pain. The compound that is responsible is called "salicin".  Salicin is too irritating to take internally, however. In the late 1800's, a German chemist made another compound that could be taken readily and that had similar properties to salicin.

This compound, acetylsalicylic acid, could be taken orally and was an effective analgesic, anti-inflamatory, and antipyretic drug and is probably the most widely used drug in the world today. Interestingly, we only learned how aspirin actually functions in the last 30 years.  Aspirin inhibits the synthesis of certain prostaglandins.

Coca and Cocaine

The Indians of Andean South America have long used coca leaves (from Erythroxylum coca, Erythroxylaceae) as a stimulant. The Indians chewed the leaves mixed with lime to free the alkaloids. The alkaloids reduced feelings of hunger and pain. Later when the alkaloids were isolated, it was discovered that they had local anesthetic properties. Cocaine has been used for surgery (especially dental surgery).

Steroids from plants

Many types of animal hormones are steroids.  Although the steroids from plants are similar, most do not have pronounced hormonal activity in animals and ordinarily must be chemically modified before use. The most commonly used plant source of steroids is Dioscorea spp. (Dioscoreaceae). These are viny plants with large tuberous roots.

These steroids occur as complex glycosides (that is, they have sugars attached) that give them soap-like properties and are sometimes called saponins. These compounds are relatively common in plants. Dioscorea species are used because they have relatively large amounts of saponins and the structure of the aglycone is particularly appropriate for conversion to the desired steroids.

Steroids from these plants are converted chemically into hormonally active substances that simulate pregnancy and serve as antifertility or contraceptive compounds or as anti-inflamatory drugs such as cortisone etc. that are used to treat a number of diseases such as arthritis etc.

Cardiac glycosides

The use of plants to treat heart disease goes back thousands of years and is found in several cultures. One of the plants found in the folk medicine of Europe is Digitalis purpurea (Scrophulariaceae).

In 1775, William Withering, a British physician documented that patients treated with foxglove improved.  He standardized the dosage of the drug. Digitalis became accepted and today is widely used in treatment of dropsy, a condition associated with congestive heart failure. The active compounds are saponins, but have an aglycone with a special type of structure.

Reference
Introduction to Pharmacognosy | Crude drugs | Natural products Introduction to Pharmacognosy | Crude drugs | Natural products Reviewed by gafacom on September 05, 2020 Rating: 5

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