Pharmacognosy: Chemical Compound and Drugs

The term comes from two Greek words: “pharmakon” meaning drug or medicine, and “gnosis” meaning knowledge. The American Society of Pharmacognosy defines pharmacognosy as “the study of the physical, chemical, biochemical and biological properties of drugs, drug substances or potential drugs or drug substances of natural origin as well as the search for new drugs from natural sources”.

Plant preparations are said to be medicinal or herbal when they are used to promote health beyond basic nutrition. The study of drugs from plants includes the subjects of botany, chemistry and pharmacology.

Botany includes the identification (taxonomy), genetics, and cultivation of plants. Chemical characterization includes the isolation, identification and quantification of constituents in plant materials. Pharmacology is the study of the biological effects that the chemicals in medicinal plants have on cell cultures, animals and humans. The renaissance of herbal medicine creates a demand for studies in the field of pharmacognosy. From a practical perspective this includes: * quality control (identity, purity, consistency).

* efficacy (therapeutic indications, clinical studies, pharmacological investigations) * safety (adverse reactions, drug interactions, contraindications, precautions) Quality Control 1. Moisture Determination/Water Content Determination * Many drugs in the U. S. P. and N. F. contain varying quantities of water either as water of crystallization (hydrates) or as water in the adsorbed from. i. Water of crystallization is water that occurs in crystals but is not covalently bonded to a host molecule or ion.

* “water of crystallization” refers to water that is found in a crystalline framework of a metal complex but that is not directly bonded to the metal ion. * A salt with associated water of crystallization is known as a hydrate. a. CuSO4•5H2O – copper (II) sulfate pentahydrate b. CoCl2•6H2O – cobalt (II) chloride hexahydrate c. SnCl2•2H2O – stannous (or tin (II)) chloride dehydrate * CuSO4•5H2O weighs more than one mole of CuSO4.

* Purpose of the method: ii. To ensure uniformity in the official drugs – -t is necessary that the U. S. P. and N. F.specify certain water-content limits in the drug monograph iii. To sell drugs with guaranteed assay for active constituent- the percent active constituent must be calculated on the basis of the moisture-free drug iv.

In scientific works , moisture or water content of crude drugs and other substances must usually be accurately determined- variable quantities would adversely affect the calculated results * Methods: v. Gravimetric – for drugs containing no constituents other than water, volatile at 105°C * The weight loss of the drug represents the moisture present in the sample vi.

Gravimetric- for drugs containing ether-soluble constituents volatile at 105°C * For drugs containing volatile oils, ethers, esters, amines vii. Azeotropic (toluene distillation) viii. Titrimetric (Karl Fischer) ix. Dew poit x. Electrolytic hygrometric * Most official chemical compounds are relatively stable with respect to their moisture content at room temperatures; that is, they never gain nor lose more than slight traces of water. Some of them are hygroscopic and absorb water readily.

Others lose part or all of their water of crystallization unless properly preserved (Copper sulfate) * Control of the amount of water contained in chemicals including plant drugs is important in making solutions of definite concentration and in the determination of the dosage substances used as medicaments * Therefore many crystalline compounds that contain water of hydration or adsorb water are subject to a limit test under the heading “Water” which specifies a determination of the water content by titration with Karl Fischer reagent (methanol solution of iodine, sulfur dioxide) 2. Ash Determination.

* Ash content * Generally taken to be the residue remaining after incineration * It represents the inorganic salts naturally occurring in the drug and adhering to it. * It may also include inorganic matter added for the purpose of adulteration (Adulterants are chemical substances which should not be contained within other substances) * Ash determination * furnishes a basis for judging the identity and cleanliness of a drug and gives information relative to its adulteration with inorganic matter * Ash standards * Set a maximum limit on the total ash or on the total acid-insoluble ash permitted.

* Acid insoluble ash is the part of the total ash which is insoluble in diluted HCl * The ash or residue yielded by an organic chemical compound (such as the plant drug) is, as a rule, a measure of the amount of inorganic matter (e. g. calcium compounds) present as impurity.

In most cases the inorganic matter is present in small amounts which are difficult to remove (that’s why they set a maximum limit on the total ash) in the purification process and which are not objectionable (which may mean that the ash content will not affect the quality of the plant drug or limited effect only)if only traces are present.

* However, it is necessary to control the amount of inorganic matter that may be contained in such substances as alkaloidal salts, especially when the substance is intended for hypodermic administration. xi. Example: acetazolamide may have a maximum of residue limit of 0. 1% (of weight of the sample used), aspirin- 0. 05% xii. 0. 1 % of 1 g acetazolamide (weight of the sample incinerated) is 0. 001 g which means that the total ash after incineration must not exceed 0. 001 g.

* Apparatus:xiii. Electric furnace- used in ignition xiv. Temperature equivalents Descriptive term| Temperature in ° C| Very dull-red heat| 500 – 550| Dull-red heat| 550 – 700| Bright-red heat| 800 – 1000| Yellow-red heat| 1000 – 1200| White heat| 1200 – 1600| * All these temperatures are within the limits of the ordinary Bunsen burner Example of ash limit of some official vegetable drugs substance| Total ash,%| Acid-insoluble ash, %| USP| | | Acacia| 4. 0| 0. 5| NF| | | Plantago seed| 4. 0| 1. 0|.

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