2.3.1 Digitalis
Synonyms Foxglove; Purple foxglove; Fairy gloves; Digifortis; Digitora; Pil-Digis; Neodigitalis.
Biological Source Digitalis comprises of the dried leaves of Digitalis purpurea L., belonging to the family Scrophulariaceae. [The word purpurea has been derived from the purple colour of flowers]. It is pertinent to mention here that the fresh leaves must be dried immediately in the dark at a temperature not exceeding 60°C so that the final dried leaves should not contain more than 5% of inherent moisture. This is, however, extremely important to retain the glycosides in a good undecomposed condition.
Geographical Source It is grown in Southern and Central Europe, England, Holland, Germany, United States and India. In India, it is grown in Kashmir and Nilgiri Hills.
Preparation Good quality digitalis is grown specifically from the seeds of selected strains that will invariably yield only leafy plants enriched with glycoside contents. Even the soil is usually sterilized by steam before commencement of sowing. Mostly it grows both appreciably and luxuriantly at an altitude ranging between 1600-300 meters preferably in a shady environment. In actual practice, the sowing of seeds is performed in autumn (October/November) , and the seedlings are virtually transplanted in the fields in the following springs (March/ April). The leaves are normally hand picked in the afternoon during August / September in the first and second year, when almost 2/3rd of the flowers have fully bloomed. The leaves collected in the first year are found to contain the highest percentage of glycosides. The basal leaves and the ones located at the top are collected at the end.
The discoloured leaves are sorted out and rejected outright. The selected leaves are duly spread on perforated trays (usually a thin bed), the trays are stacked one above the other in a well-closed dark drying shed heated by a stream of hot air maintained strictly at a temperature not more than 60°C.
The dried leaves having a misture content not more than 5% are carefully packed in suitable air-tight containers, charged with appropriate dehydrating agents and shipped for export.
Note The therapeutic potency vis-à-vis the activity of the leaves is solely due to the glycoside content. Surely, the presence of moisture and certain enzymes, namely; oxidase and digipurpuridase, are chiefly responsible for the ultimate deterioration of the glycosides of the leaves. In case, the leaves are made to dry at a temperature beyond 60oC, it has been observed that there is a drastic loss in potency on account of chemical degradation (irreversible).
Description
Colour : Dark greyish green
Odour : Slight
Taste : Bitter
Size : Length: 10-14 cm; width: 4-15 cm
Shape : Orate-lanceolate to broadly ovate
Special Features The digitalis leaves are more or less pubescent venation together with pronounced and marked veinlets on the under surface. The leaves are invariably crumpled and broken.
Chemical Constituents Nativelle (1868), Kiliani (1891), and Stoll (1938) were the pioneers who contributed valuable informations with regard to the chemical constituents present in digitalis through their extensive and intensive studies.
It has been reported that digitalis essentially contains three important primary glycosides namely: Purpurea glycoside A, Purpurea glycoside B, and Purpurea glycoside C, which upon hydrolysis give rise to digitoxin, gitoxin and gitalin respectively. These secondary glcosides on further hydrolysis yields noncarbohydrate moieties (called aglycones or genins) digitoxigenin, gitoxigenin and gitaligenin or gitaloxigenin respectively. The series of all these hydrolysed products and their structures are summarised below.
Besides, the crude drug also contains a good number of other glycosides (e.g.; digitalin, diginin); saponins (e.g.; digitonin, gitin and digitosaponin); tannins, gallic, formic, acetic, succinic and benzoic acids; fatty acids and enzyme digipuridase solely responsible for hydrolysis of purpurea glycosides.
Chemical Tests A plethora of chemical colour reactions have been evolved to be used as the qualitative tests either for the various glycosides or their corresponding aglycones in the chemical laboratory. However, the exact positions of the respective glycosides or their aglycones may be detected either on the paper charomatograms or on the thin layer chromatographic plates by virtue of the production of specific colours or by exposing the chromatograms under UV light so that the components would be detcted by their fluorescence. All these specific tests are summarised in Table 4.1.
Table 4.1 Colour Tests of Glycosides
* Baljet Reagent: Aqueous solution of picric acid (1% w/v) and NaOH soln. (10% w/v). Both solutions mixed immediately before use and filtered.
** Raymond’s Reagent: A 1% (w/v) solution of m-dinitrobenzene in ethanol (or methanol)
*** Tollen’s Reagent: To a 0.1 N soln. of AgNO3 is added dilute NH4OH till the white precipitate intially formed gets dissolved after further addition of NH4OH.
**** Xanthydrol Reagent: A solution of 0.125% (w/v) xanthydrol in glacial acetic acid containing 1% HCl.
***** Kedde’s Reagent: Mix equal volumes of a 2% (w/v) soln. of 3, 5 dinitrobenzoic acid in methanol and a 7.5% (w/v) aqueous soln. of KOH
Substituents/Adulterants The digitalis leaves have been frequently adulterated with the following varieties of leaves, namely:
1. Great mullein leaves: The leaves of Verbascum thapsus belonging to the family Scrophularineae are usually mixed with the genuine drug leaves which may be identified and distinguished microscopically by the abundant presence of huge woolly and branched candelabra trichomes.
2. Primose leaves: The leaves of Primula vulgaris belonging to the family Primulaceae are invariably mixed to digitalis, that may be identified microscopically as follows:
(a) P. vulgaris has uniseriate covering trichomes , that are normally 8-9 celled long, and
(b) P. vulgaris leaves have straight lateral veins.
3. Comfrey leaves: The leaves of Symphytum officinale belonging to the family Boraginaceae are mixed with digitalis, which may be distinguished by the presence of multicellular trichomes seen at the top in the shape of a hook.
Uses
1. Digitalis enhances the force of contradiction of heart muscle which ultimately affords an increased carrdiac output, decreased size of heart, decreased venous pressure and above all the decreased blood volume. Hence, digitalis together with its various marketed preparations are employed profusely as vital cardiotonics in the management and control of different kinds of congestive heart failure, atrial flutter, atrial fibrillation, supraventricular tachycardia and premature extra systoles.
2. Digitalis has a tendency to exert an overall cumulative effect in the body, and hence it gets eliminated rather gradually. Therefore, it is extremely important to monitor the dosage regimen by a physician whether he relies on branded products or natural drug preparations eg., Digitoxin injection, Lanoxin, Prepared digitalis and Digitalis tinture.
