Foxglove

Information
Application
Notes
References

Photo: Matthijs Photography, Pixabay

Botanical name

Digitalis purpurea L.

Family

Plantaginaceae

Common name

Common foxglove, Purple foxglove, Lady’s glove

Information about the plant

Foxglove is a poisonous plant (!) native to Europe and is particularly widespread on the western coast of Norway, in Great Britain, Germany, the Atlantic and sub-Atlantic regions of France, Belgium, and the Netherlands, as well as in the Pyrenees and the Atlantic parts of the Iberian Peninsula. It is also found on the American continent, including in Chile and Argentina. Foxglove grows in semi-shaded clear-cut areas, in forest clearings, and on bushy slopes.

The name derives from the shape of the flower, which resembles a thimble. This is also reflected in the Latin genus name Digitalis, which derives from the Medieval Latin ‘digitale’, referring to a thimble as a tailor’s tool. The specific epithet purpurea refers to the purple color of the flower.

Foxglove is a biennial plant. In the first year, it forms a basal rosette; in the second year, a flowering stem up to 2 m tall grows from its center. The leaves, both those of the rosette and those on the stem, are downy on the upper surface and grey-tomentose on the underside. The lower leaves are long-stalked, while those higher up are increasingly sessile. Numerous flowers hang down on bracts on the upper part of the stem in a loose, one-sided cluster, each sitting in a small, pointed calyx. The purple flowers are tubular and bell-shaped, 4 to 5 cm long, with a short upper lip and a longer, three-lobed lower lip. Dark spots with light-colored edges can be seen on the inside of the lower lip. The flower gives the appearance of an ‘abundance of pollen’ to attract bees for pollination. The fruit is an ovoid, hairy capsule enclosed by the calyx. The flowering time is from June to July.

Medicinally used parts of plants (herbal drug)

The dried leaves (Digitalis purpurea leaves – Digitalis folium) are used. The rosette leaves from the first year of growth are usually harvested in early autumn for economic reasons.

The commercially available herbal drug comes from cultivated plants in the Balkan countries, Austria, and Switzerland.

Constituents of the herbal drug

Digitalis purpurea leaves (foxglove leaves) contain numerous cardiac steroids in the form of cardenolides (cardenolide glycosides). The most important of these are purpurea glycosides A, B, and E, with the aglycones digitoxigenin, gitoxigenin, and gitaloxigenin. Other compounds include steroid saponins and pregnane glycosides. Cardenolides are responsible for the toxicity of the plant.

Quality of the drug

The quality of Digitalis purpurea leaves (Digitalis purpureae folium) is specified in the European Pharmacopoeia (Ph. Eur.). The quality of the standardized Digitalis purpurea powder was specified in the German Pharmacopoeia (DAB) until 2014. The European Pharmacopoeia also contains a quality specification for ‘Digitalis for homeopathic preparations’.

Medical applications

Recognised medical use

In the past, foxglove leaves were used in folk medicine to treat heart failure. Due to the narrow therapeutic index (the cardenolides are highly toxic!), this treatment is problematic and should no longer be practiced. Digitalis purpurea leaves and the cardenolides isolated from them are highly potent medicinal substances and must not be used in phytotherapy. Therefore, Digitalis purpurea leaves have not been assessed by the HMPC and ESCOP.

The pharmaceutical market offers finished medicinal products containing cardenolides (digitoxin and gitoxin) isolated from foxglove leaves. These are prescribed by doctors for heart failure and must be taken in the correct dosage. The cardenolides used to treat heart failure are, however, now preferably obtained from the woolly foxglove (Digitalis lanata L.). The pure substances digitoxin, acetyldigoxin, and lanatoside C, which are available on the market, are isolated from its leaves.

Traditional use

Due to their content of potent cardiac glycosides, which are also responsible for the toxicity of the plant, the leaves of Digitalis purpurea are not classified as a traditional herbal medicinal product (Article 16a of Directive 2001/83/EC).

Herbal drug preparations in finished dosage forms

None. Only finished medicinal products containing isolated cardenolides are available on the market.

Dosage

These products should only be used under medical supervision and at individually determined doses.

Preparation of a tea

Not applicable.

Notes

Digitalis purpurea leaves are poisonous (they have a strong effect on the heart!), so the herbal drug or any finished medicinal products should only be used under medical supervision.