Drugs are substances that are used or intended to be used in the diagnosis, prevention, treatment or cure of diseases. In early times, these substances were derived from natural sources, of which plants took up the major share. With the introduction of technology, most drugs today are manufactured synthetically in the laboratory. The major sources of drugs can be grouped into the following
A number of plants have medicinal qualities and have been used for centuries as drugs or drug sources. Although the earliest plant source for drugs was the leaf, other parts of plants (e.g., barks, fruits, roots, stem, wood, seeds, blossoms, bulb etc.) were also later exploited for drug extraction. Where the product is used without further processing e.g., ground leaves or bark, boiled concoctions or powdered sap, the substance is called crude drug.
The table below shows some pharmacologically active principles or drugs derived from various parts of a plant.
|Leaves||Digoxin, digitoxin (from Digitalis purpurea/foxglove plant); atropine (from Atropa belladonna)|
|Flowers||Vincristine, vinblastine (from Vinca rosea)|
|Fruits||Physostigmine (from Physostigma venenosum/calabar bean)|
|Seeds||Strychnine (from Nux vomica); physostigmine (from Physostigma venenosum/calabar bean)|
|Roots||Emetine (from Cephaelis ipecacuanha); reserpine (from Rauwolfa serpentina)|
|Bark||Quinine (from Cinchona); atropine (from Atropa belladonna)|
|Stem||Tubocurarine (from Chondrodendron tomentosum)|
Many important drugs are derived from animal source. In most instances, these medicinal substances are derived from the animal’s body secretions, fluid or glands. Insulin, heparin, adrenaline, thyroxin, cod liver oil, musk, beeswax, enzymes, and antitoxins sera are some examples of drugs obtained from animal sources. Like plant products, drugs from animal sources may be crude (unrefined) or refined material.
Several life-saving drugs have been historically derived from microorganisms. Examples include penicillin produced by Penicillium chrysogenum, streptomycin from Streptomyces griseus, chloramphenicol from Streptomyces venezuelae, neomycin from Streptomyces fradiae, bacitracin from Bacillus subtilis etc. Xanthan (polysaccharide gum secreted by Xanthomonas campestris), dextran (polysaccharide of glucose synthesized by lactic acid bacteria Leuconostoc mesenteroides, Streptococcus mutans, Lactobacillus brevis), curdian (β-1,3-glucan polymer, product of Agrobacterium biobar and Alcaligenes faecalis), pullulan (a polysaccharide polymer of maltotriose units produced from starch by the fungus Aureobasidium pullulans) etc. are all examples of drugs from microbial sources.
Read Also: Microorganisms of Pharmaceutical Interest
Bioactive compounds from marine flora and fauna have extensive past and present use in the prevention, treatment or cure of many diseases. Coral, sponges, fish, and marine microorganisms produce biologically potent chemicals with interesting anti-inflammatory, anti-viral, and anticancer activity. For example curacin A from marine cyanobacterium Lyngbya majuscule, eleutherobin from coral Eleutherobia sp., discodermolide from marine sponge Discodermia dissoluta, etc. show potent anti-tumour activity.
Minerals (both metallic and non-metallic minerals) have been used as drugs since ancient times. Our body requires trace elements of minerals in order to maintain homeostasis. Patients lacking an adequate level of these materials may take specific mineral-based drugs to raise the level of minerals.
Examples include ferrous sulfate in iron deficiency anemia; magnesium sulfate as purgative; magnesium trisilicate, aluminum hydroxide and sodium bicarbonate as antacids for hyperacidity and peptic ulcer; zinc oxide ointment as skin protectant, in wounds and eczema; gold salts (solganal, auranofin) as anti-inflammatory and in rheumatoid arthritis; selenium as anti-dandruff.
Radioactive isotopes of iodine, phosphorus, gold are employed for the diagnosis/treatment of diseases particularly malignant conditions.
A synthetic drug is produced using chemical synthesis, which rearranges chemical derivatives to form a new compound. The synthetic sources of drugs evolved with human skills in the laboratory and advanced knowledge and understanding of phytochemical investigation. At present, majority of drugs used in clinical practice are exclusively prepared synthetically in pharmaceutical and chemical laboratory.
One of the earliest synthetic drugs was sulphonamide, which began with the synthesis of prontosil dye. Other examples include acetylsalicylic acid (aspirin or ASA), oral antidiabetics, antihistamines, thiazide diuretics, chloroquine, chlorpromazine, general and local anaesthetics, paracetamol, phenytoin etc.
Synthetically manufactured drugs generally have higher yields that are significantly associated with quality, purity and low cost.
Semi-synthetic drugs are neither completely natural nor completely synthetic. They are a hybrid and are generally made by chemically modifying substances that are available from natural source to improve its potency, efficacy and/or reduce side effects. Sometimes, semi-synthetic processes are used to prepare drugs when the natural sources may yield impure compounds or when the synthesis of drugs (complex molecules) may be difficult, expensive, and commercially unviable.
In semi-synthetic drugs, the nucleus of drug obtained from natural source is kept intact but the chemical structure is altered. Examples of semi-synthetic medicine include heroin from morphine, bromoscopolamine from scopolamine, homatropine from atropine, ampicillin from penicillin etc.
This is relatively a new field which is being developed by mixing discoveries from molecular biology, recombinant DNA technology, DNA alteration, gene splicing, immunology, and immune pharmacology. Drugs developed using living organisms with the help of biotechnology or genetic engineering are known as biologics, biopharmaceuticals, recombinant DNA expressed products, bioengineered, or genetically engineered drugs Examples include recombinant Hepatitis B vaccine, recombinant insulin and others.
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