Inert Constituents

The chemical compounds, though present in plant and animal kingdom, which do not possess any definite therapeutic values as such but are useful as an adjunct either in the formulation of a ‘drug’ or in surgery are collectively known as inert constituents.

(a) Plant Drugs: The following inert constituents are invariably present in plants, namely:

Cellulose : Microcrystalline forms of cellulose are used as combination binderdisintegrants in tabletting. Collodal cellulose particles aid in stabilization and emulsification of liquid;

Lignin : To precipitate proteins, and to stablise asphalt emulsions;

Suberin : Esters of higher monohydric alcohols and fatty acids;

Cutin : -do-

Starch : As pharmaceutic aid i.e.; tablet filler, binder and disintegrant;

Albumin : Soyabean albumins–as emulsifiers;

Colouring Matters : Cochineal for colouring food products and pharmaceuticals.

(b) Animal Drugs: The under mentioned inert constituents are mostly present in animals, namely:

Keratin : For coating “enteric pills” that are unaffected in the stomach but dissolved by the alkaline into intestinal secretions;

Chitin : Deacylated chitin (chitosan)–for treatment of water; sulphated chitin–

as anticoagulant in laboratory animals.

It has been observed that the very presence of ‘Inert Constituents’ either act towards modifying or check the absorbance and the therapeutic index of the ‘active constituents’.

Obviously, to get at the right active constituents one has to get rid of the host of ‘inert constituents’ by adopting various known methods of separation, purification and crystallization. Therefore, most literatures invariably refer to the former as ‘secondary’ plant products.

The presence of these secondary plant products (active constituents) are governed by two school of thoughts, namely:

(a) Superfluous Metabolites: i.e., substances that have no value as such and perhaps their presence are due to the lack of exceretory mechanism in them and ultimately result as the ‘residual lock-up’ superfluous metabolites, and

(b) Characteristic Survival Substances: i.e., substances which exert a positive survival value on the plant wherein they are actually present. They offer more or less a ‘natural defencemechanism’ whereby these host plants are survived from destruction owing to their astringent, odorous and unpalatable features.

Examples: Poisonous alkaloidal containing plants; astringent containing shrubs; and pungent volatile oil-containing trees etc.

1. Genetic Composition (or Heredity): In reality, genetic effects exert both qualitative and quantitative alterations of the active constituents in medicinal plants.

(i) Eugenol: It is naturally present in two different species in varying quantities as follows:

Eugenia caryophyllus (Sprengel) Bullock et Harrison: 70–95%

Syzgium aromaticm (L.) Merr et L.M. Perry: Not less then 85%.

(ii) Reserpine-rescinamine group of Alkaloids:

Rauvolfia serpentina (Linné) Bentahm: NLT* 0.15%;

Rauvolfia vomitoria Afzelius (from Africa): NLT 0.20%;

(*NLT: Not less than)

(iii) Rutin:

Fagopyrum esculatum Moznch : 3-8%;

Sophora japonica Linné : 20%;

(iv) Menthol:

Mentha piperita L. : 50-60%

Mentha arvensis Linnévar : 75-90%

(Japanese Mint Oil)

The environment factors largely contribute to the quantitative aspect of secondary constituents i.e., active constituents. It is pertient to mention here that medicinal plants belonging to the same species which are phenotypically identical i.e., they essentially bear a close resemblance with regard to their form and structure, may not, however, genotypically be the same i.e., possessing the same genetic composition. This particular natural phenomenon evidently gives rise to an altogether marked and pronounced difference in their chemical composition, specially with reference to active constituents. In a more logical and scientific manner it may be said that these plants categorically belong to different chemical races.

(i) Ergotamine: Modified strains of Claviceps purpurea (Fries) have been developed, exclusively for field cultivation, that are capable of producing nearly 0.35% of ergotamine (in comparison to the normal one producing NLT 0.15% of total ergot alkaloids).

(ii) Eucalyptol (Syn: Cineole, Cajeputol ): It is present in the fresh leaves of Eucalyptus globus Libillardiere to the extent of 70–85%. It has been observed that the chemical races of some species of Eucalyptus invariably display significant variations in the content of eucalyptus and related components present in the essential oils.

There are a number of environmental factors which may afford considerable changes in active plant constituents, for instance: composition of soil (mineral contents); climate (dry, humid, cold); associated flora (Rauvolfia serpentina and R. vomitoria) and lastly the methods of cultivation (using modified strains, manual and mechanical cultivation). For a specific instance it may be recalled that a soil rich-in-nitrogen content evidently gives rise to a relatively higher yield of alkaloids in the medicinal plants; whereas a soil not so abdundant in nitrogen content and grown in comparatively dry zones may yield an enhanced quantum of volatile oil.

3. Ontogeny (or Ageing of Plant): The age of a medicinal plant has a direct impact on the concentration of the ‘active constituent’. It is, however, not always true that older the plant greater would be the active principal.

(i) Cannabidiol: It is present in Cannbis sativa L. (C sativa var. Indica Auth), possessing

euphoric activity; and its content attains a maximum level in the growing season and subsequently the decline commences gradually. Interestingly, the concentration of dronabinol (or tetrahydrocannabinol) starts to enhance reciprocally till the plants gets fully matured.

(ii) Morphine: The well-known narcotic-anlagesic present in the air-dried milky exudate

collected by incising the capsules of Papaver somniferum Linné or P. album Decandolle is found to be the highest peak just 2 to 3 week after flowering. An undue delay in harvesting from this ‘critical-period’ would ultimately result into the decomposition of morphine. It is worth to be noted that a prematured harvesting of latex would certainly enhance the content of allied alkaloid like codeine and thebaine.

In short, it is a prime importance to affect the harvesting of medicinal plant at the right time so as to maximise the yield of the active principal.