Drug and Active Principle
Until the end of the 19th century, medicines were natural organic or inorganic products, mostly dried, but also fresh, plants or plant parts. These might contain substances possessing healing (therapeutic) properties or substances exerting a toxic effect.
In order to secure a supply of medically useful products not merely at the time of harvest but year-round, plants were preserved by drying or soaking them in vegetable oils or alcohol. Drying the plant or a vegetable or animal product yielded a drug (from French “drogue” – dried herb). Colloquially, this term nowadays often refers to chemical substances with high potential for physical dependence and abuse. Used scientifically, this term implies nothing about the quality of action, if any. In it’s original, wider sense, the drug could refer equally well to the dried leaves of peppermint, dried lime blossoms, dried flowers and leaves of the female cannabis plant (hashish, marijuana), or the dried milky exudate obtained by slashing the unripe seed capsules of Papaver somniferum (raw opium). Nowadays, the term is applied quite generally to a chemical substance that is used for pharmacotherapy.
Soaking plants parts in alcohol (ethanol) creates a tincture. In this process, pharmacologically active constituents of the plant are extracted by the alcohol. Tinctures do not contain the complete spectrum of substances that exist in the plant or crude drug, only those that are soluble in alcohol. In the case of opium tincture, these ingredients are alkaloids (i.e., basic substances of plant origin) including morphine, codeine, narcotine = noscapine, papaverine, narceine, and others.
Using a natural product or extract to treat a disease thus usually entails the administration of a number of substances possibly possessing very different activities. Moreover, the dose of an individual constituent contained within a given amount of the natural product is subject to large variations, depending
upon the product‘s geographical origin (biotope), time of harvesting, or conditions and length of storage. For the same reasons, the relative proportion of individual constituents may vary considerably. Starting with the extraction of morphine from opium in 1804 by F. W. Sertürner (1783–1841), the active principles of many other natural products were subsequently isolated in chemically pure form by pharmaceutical laboratories.
The aims of isolating active principles are:
- Identification of the active ingredient(s).
- Analysis of the biological effects (pharmacodynamics) of the individual ingredients and of their fate in the body (pharmacokinetics).
- Ensuring precise and constant dosage in the therapeutic use of chemically pure
- The possibility of chemical synthesis, which would afford independence from limited natural supplies and create conditions for the analysis of structure-activity
Finally, derivatives of the original constituent may be synthesized in an effort to optimize pharmacological properties. Thus, derivatives of the original constituent with improved therapeutic usefulness may be developed.
image: From poppy to morphine
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