Figure 1. Hierarchical Classification of Drugs
Introduction
Medicines can be separated into two broad groups. The first is ‘Synthetic Medicines‘. As the name suggests they are created through supervised chemical synthesis. The associated chemical reactions are relatively simple and often sequential. The final active substances produced are small molecules with relatively simple chemical structures, an example being aspirin (Figure 2).
Natural Products
Figure 2. Aspirin Molecule (Black balls represents Carbon atoms)
By contrast natural products are derived from comparatively complex starting materials sourced from the ‘Natural Environment‘. More specifically, they are derived from living organisms or their by-products. Traditionally, these living organisms have been plants from which relatively complex compounds have been extracted, purified and used as medicines. In some cases these compounds have been chemically-modified giving rise to ‘Semi-synthetic‘ drugs. An example from this group is paclitaxel which is derived from bark extracts of the Pacific Yew Tree (Taxus brevifolia) (Craig & Stitzel, 1994: 694) and used to treat various cancers.
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Recombinant Products
The most structurally complex group of pharmaceuticals is a sub-group of ‘Natural Products‘ that are termed ‘Recombinant Products‘. They are derived from ‘Natural Sources‘ but the genetic material (DNA) coding for these products in living organisms is deliberately altered to yield a product with specific characteristics.
Figure 3. Space-filling diagram of Monoclonal Antibody (Black balls represent carbon atoms)
This is commonly referred to as “Genetic Engineering (GE)” and results in proteins which typically are not found in nature. Invariably the process requires ‘combining‘ genetic material from different species so the term ‘Recombinant‘ is included in the name of the final product to reflect this. One such example is, ‘Recombinant Interferon alpha-2b‘ (Rieger, 1995: 71).
A major distinction between conventional ‘small-molecule‘ pharmaceuticals and this newer class of recombinant proteins is molecular weight and structural complexity. As suggested by Figure 2, Aspirin, an example of a conventional pharmaceutical product is relatively small and structurally simple. This contrasts significantly with the diagram of a ‘monoclonal antibody (mAb)‘ in Figure 3 which falls in the category of large, highly complex ‘recombinant proteins‘. The scale in both diagrams is not equal but in both cases the black / dark grey balls represent Carbon atoms. With a little imagination, it becomes clear that were they represented to equal scale, the mAb would be many hundreds and possibly thousands of times larger and more complex than aspirin. This single difference has many implications for use and storage of recombinant proteins and many of these implications will be explored in greater detail in future posts.
References
- Craig,C.R. & Stitzel, R.E. (1994) Modern Pharmacology. 4th ed. Boston: Little, Brown and Company.
- Rieger, P.T. (1995) Biotherapy: A Comprehensive Overview. 1st ed. London: Jones and Bartlett Publishers International.
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14 Comments on “Classification of Pharmaceuticals: Biologics vs. Conventional Medicines”
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