Digitalis Leaf

Digitalis

 

(Ph Eur monograph 0117)

 

Ph Eur


 

 

Definition

 

Digitalis leaf consists of the dried leaf of Digitalis purpurea L. It contains not less than 0.3 per cent of cardenolic glycosides, expressed as digitoxin (Mr 765), and calculated with reference to the drug dried at 100C to 105C.

 

Characters

 

Digitalis leaf has a faint but characteristic odour. The whole leaf is about 10 cm to 40 cm long and 4 cm to 15 cm wide. The lamina is ovate lanceolate to broadly ovate. The winged petiole is from one quarter as long as to equal in length to the lamina.

 

It has the macroscopic and microscopic characters described in identication tests A and B.

 

Identification

 

A.    The leaf is brittle and often occurs broken. The upper surface is green and the lower surface is greyish-green. The apex is subacute and the margin is irregularly crenate, dentate or serrate. The base is decurrent. The venation is pinnate, the lateral veins being prominent especially on the lower surface, leaving the midrib at about 45C and anastomosing near the margin; a veinlet terminates in each tooth of the margin and the lower veins run down the winged petiole. The upper surface is rugose and pubescent; the lower surface shows a network of raised veinlets and is densely pubescent.

 

B.    Reduce to a powder (355). Examine under a microscope using chloral hydrate solution R. The powder shows the following diagnostic characters: epidermal cells with anticlinal walls which are straight or slightly sinuous on the upper surface and markedly sinuous on the lower surface; the cuticle is smooth. Trichomes are of two types: uniseriate, bluntly pointed non-glandular, usually of three to five cells, often with one or more collapsed cells, walls mostly finely warty or faintly striated; glandular trichomes usually with a unicellular, sometimes a multicellular uniseriate stalk and a unicellular or bicellular or exceptionally tetracellular head. Anomocytic stomata (2.8.3) are absent or very rare on the upper surface, numerous on the lower surface. Calcium oxalate crystals and sclerenchyma are absent.

 

C.    Examine by thin-layer chromatography (2.2.27), using silica gel G R as the coating substance.

 

Test solution

 

To 1.0 g of the powdered drug (180) add a mixture of 20 ml of alcohol  (50 per cent V/V) R and 10 ml of lead acetate solution R. Boil for 2 min, allow to cool and centrifuge. Shake the supernatant solution with two quantities, each of 15 ml, of chloroform R; separate the two layers by centrifugation if necessary. Dry the chloroform layers over anhydrous sodium sulphate R and filter. Evaporate 10 ml of the solution to dryness on a water-bath and dissolve the residue in 1 ml of a mixture of equal volumes of chloroform R and methanol  R.

 

Reference solution

 

Dissolve 5 mg of purpureaglycoside A CRS, 2 mg of purpureaglycoside B CRS, 5 mg of digitoxin R and 2 mg of gitoxin R in a mixture of equal volumes of chloroform R and methanol  R and dilute to 10 ml with the same mixture of solvents.

 

Apply separately to the plate as bands 2 cm by 0.3 cm 20 ml of each solution. Develop over a path of 10 cm using a mixture of 7.5 volumes of water  R, 10 volumes of methanol  R and 75 volumes of ethyl acetate R. Allow the solvents to evaporate. Spray with a mixture of 2 volumes of a 10 g/l solution of chloramine R and 8 volumes of a 250 g/l solution of trichloroacetic acid R in alcohol  R. Heat at 100C to 105C for 10 min. Examine in ultraviolet light at 365 nm. The chromatogram obtained with the reference solution shows a zone of light-blue fluorescence in the lower part of the chromatogram, corresponding to purpureaglycoside B, and just above it a zone of brownish-yellow fluorescence, corresponding to purpureaglycoside A. A zone of light-blue fluorescence, corresponding to gitoxin, appears in the middle of the chromatogram and above it a zone of brownish-yellow fluorescence, corresponding to digitoxin. The zones in the chromatogram obtained with the test solution are similar in position, colour and size to the zones in the chromatogram obtained with the reference solution. Other zones of fluorescence may also appear in the chromatogram obtained with the test solution.

 

D.    Evaporate 5 ml of the chloroformic solution obtained in identification test C to dryness on a water-bath. To the residue add 2 ml of dinitrobenzoic acid solution R and 1 ml of 1M sodium hydroxide. A reddish-violet colour develops within 5 min.

 

E.    Evaporate 5 ml of the chloroformic solution obtained in identification test C to dryness on a water-bath. To the residue add 3 ml of xanthydrol  solution R and heat on a water-bath for 3 min. A red colour develops.

 

Tests

 

Foreign matter  (2.8.2)

 

There are no leaves with few or no trichomes and epidermal cells showing, in surface view, beaded anticlinal walls (Digitalis lanata).

 

Loss on drying (2.2.32)

 

Not more than 6.0 per cent, determined on 1.000 g of the powdered drug (355) by drying in an oven at 100C to 105C.

 

Total ash (2.4.16)

 

Not more than 12.0 per cent.

 

Ash insoluble in hydrochloric acid (2.8.1)

 

Not more than 5.0 per cent.

 

Assay

 

Shake 0.250 g of the powdered drug (180) with 50.0 ml of water  R for 1 h. Add 5.0 ml of a 150 g/l solution of lead acetate R, shake and after a few minutes add 7.5 ml of a 40 g/l solution of disodium hydrogen phosphate R. Filter through a pleated filter paper. Heat 50.0 ml of the filtrate with 5 ml of hydrochloric acid (150 g/l HCl) under a reflux condenser on a water-bath for 1 h. Transfer to a separating funnel, rinse the flask with two quantities, each of 5 ml, of water  R and shake with three quantities, each of 25 ml, of chloroform R. Dry the combined chloroform layers over anhydrous sodium sulphate R and dilute to 100.0 ml with chloroform R. Evaporate 40.0 ml of the chloroformic solution to dryness, dissolve the residue in 7 ml of alcohol  (50 per cent V/V) R and add 2 ml of dinitrobenzoic acid solution R and 1 ml of 1M sodium hydroxide. At the same time prepare a reference solution as follows. Dissolve 50.0 mg of digitoxin CRS in alcohol  R and dilute to 50.0 ml with the same solvent. Dilute 5.0 ml of the solution to 50.0 ml with alcohol  R. To 5.0 ml of the resulting solution add 25 ml of water  R and 3 ml of hydrochloric acid (150 g/l HCl). Heat the solution under a reflux condenser on a water-bath for 1 h and complete the preparation as described above. Measure the absorbance (2.2.25) of the two solutions at 540 nm several times during the first 12 min until the maximum is reached, using as the compensation liquid a mixture of 7 ml of alcohol  (50 per cent V/V) R, 2 ml of dinitrobenzoic acid solution R and 1 ml of 1M sodium hydroxide.

 

From the absorbances measured and the concentrations of the solutions, calculate the content of cardenolic glycosides, expressed as digitoxin.

 

Storage

 

Store protected from light and moisture.

 

 


 Ph Eur

 

Action and use

 

Cardiac glycoside.

 

When Powdered Digitalis is prescribed or demanded, material complying with the requirements above with the exception of Identification test A and the test for Foreign matter  shall be dispensed or supplied.