Foxgloves are beautiful plants that grow in both a wild and a cultivated form. They are admired for their tall spires containing multiple rows of large, tubular flowers. Foxgloves are notable for more than their beauty, however. They contain a chemical called digitalis. Although this chemical can be dangerous, in small quantities it’s used to make a heart medicine.
Digitalis increases the force of the heartbeat. This effect is helpful in a disorder known as congestive heart failure. It also helps to treat a type of irregular heartbeat known as atrial fibrillation. There is a world of difference between taking a prescribed dose of digitalis medicine and ingesting the digitalis in a foxglove plant, however. The plant is poisonous.
The scientific name of the common foxglove is Digitalis purpurea. The species has purple, pink, yellow, or white flowers. It’s native to Europe but has been introduced to North America. The plant is very attractive and is admired by many people, despite its dangers.
It’s uncertain how the name of the foxglove plant was derived, but there are two main theories.
- A commonly accepted idea is that the name came from the Anglo-Saxon term “foxes glofa”, which means “glove of the fox”. The flowers do fit over a human finger nicely, like the fingers of a glove or like a thimble, but why the reference to foxes? Perhaps because of the legend which said that fairies gave the flowers to foxes so that they could put them on their toes and then silently approach and kill a family’s chickens.
- Some investigators have suggested that the plant name has nothing to do with foxes. Instead, they believe that the word “fox” developed from the word “folk’s”. Folk was another name for fairies.
Foxgloves are often hard to ignore when they are in bloom, especially when they’re growing in a group. The spires may be as tall as six feet. The flowers are often pink but may also be purple, lavender, yellow, peach, orange, rusty brown, or white. Some plants produce spires which have flowers of more than one colour. The opening of the flowers is often decorated with blotches of various colours.
Foxgloves are thought to be native to Europe, Asia, and Northern Africa. They have been introduced to many other parts of the world, however. There are about twenty species, most of which are biennial. In the first year of its life, a foxglove plant consists of a low rosette of leaves. It doesn’t flower until the second year. The leaves are oval in shape and have pointed tips. They are attached to the flower stem in an alternate arrangement.
The flowers, seeds, leaves, stem, and sap of foxgloves are all poisonous. Human poisoning isn’t common, however. The leaves don’t taste very good, so most people quickly spit the plant out if they sample it. However, some people have mistaken foxglove leaves for comfrey leaves and have been poisoned when they’ve made an infusion or tea from the leaves. (Comfrey is a controversial plant and is considered to be unsafe by some investigators.)
Children may be attracted to the interesting, bell-shaped flowers of foxgloves. They mustn’t be allowed to suck liquid from the bells, however, as sometimes happens, nor drink water from a vase in which the flowers have been standing.
The toxicity of a particular foxglove plant depends on several factors, including how much toxin is present in the part that is eaten and the individual susceptibility of the person who eats the plant. The symptoms resulting from foxglove ingestion range from mild gastrointestinal problems to serious nervous system and heart effects that require emergency medical treatment.
William Withering was a doctor and botanist who lived in the eighteenth century. He investigated the effects of foxglove on dropsy. “Dropsy” was the old name for a condition that we call edema today. Edema refers to the collection of fluid in body tissues. Congestive heart failure is often accompanied by edema.
Withering decided to do his research after seeing the success of a herbalist at treating dropsy. The woman give her patients a mixture of many different herbs. Withering patiently tested each component of the mixture and found that foxglove was responsible for the beneficial effects.
Withering found that an infusion of foxgloves leaves could slow and strengthen the heartbeat. He also found that a high dose of the leaves could stop the heartbeat instead of helping it. He named the active ingredient in foxglove “digitalis” after the first word in the plant’s scientific name.
The terminology concerning digitalis is sometimes confusing.
- When the chemical is inside a foxglove it’s known as digitalis.
- When digitalis from Digitalis lanata leaves is prepared as a medication it’s known as either digitalis or digoxin. Digoxin is the generic name of the medicine. A common brand name is Lanoxin.
- When digitalis from Digitalis purpurea is prepared as a medication it’s known as either digitalis or digitoxin. Digitoxin has also been obtained from some other foxglove species.
Digoxin and digitoxin have almost identical chemical structures. Digoxin has one hydroxyl group (OH) that digitoxin lacks, however. In North America, digoxin is generally prescribed instead of digitoxin.
Digitalis is a type of medication known as a cardiac glycoside. Cardiac glycosides are used to treat heart failure and an irregular heart beat (cardiac arrhythmia).
The term “heart failure” doesn’t mean that the heart has stopped beating, but it does mean that the heart can no longer pump enough blood to satisfy all the body’s needs. The disorder is also known as congestive heart failure or CHF. It develops after the heart has been damaged or weakened. As a result of the decreased effectiveness of the heartbeat, blood collects in blood vessels and fluid from the blood escapes into tissues, causing congestion.
Digitalis helps heart failure because it causes the heart to beat more strongly. Digitalis also slows the heartbeat, which is useful in the treatment of certain heart disorders.
Digitalis increases the force of the heartbeat. It does this by stimulating the buildup of calcium in heart muscle. Calcium is a vital element in the body because it enables muscles to contract.
The heart is made of muscle cells. Like other cells, heart cells are covered with a membrane, which contains proteins called receptors. Chemicals from the outer and inner environments of the cell join to the receptors, triggering certain effects as they do so.
Digitalis interferes with the action of two membrane proteins, thereby allowing calcium to build up. It does this in the following way.
- A membrane protein called the sodium-potassium pump moves potassium into the heart cells and sodium out of the cells. This activity is a normal part of a cell’s life.
- Digitalis binds to the pump and stops it from doing its job, allowing sodium to build up in the heart cells.
- The high level of sodium in a heart cell alters the activity of another membrane protein called NCX, which stands for sodium-calcium exchanger. (The “N” comes from Na, which is the chemical symbol for sodium.)
- NCX moves sodium in one direction through the cell membrane and calcium in the other direction.
- Each chemical can be carried either into the cell or out of the cell by NCX. The predominant direction of chemical flow depends on environmental conditions.
- The high level of sodium inside the cell when digitalis is present causes NCX to increase its movement of sodium out of the cell and calcium into the cell
- These changes serve to increase the amount of calcium in the heart cells, enabling the heart to contract more strongly.
The term “arrhythmia” refers to the altered rate or rhythm of the heartbeat. The heart may beat too fast, too slow, or irregularly. A common type of arrhythmia—the type that digitalis often helps—is called atrial fibrillation.
The atria are the two upper chambers of the heart, which contract before the two lower chambers, or ventricles. During atrial fibrillation, the atria quiver or flutter rapidly instead of contracting. This process interferes with blood flow through the heart.
The sinoatrial node, or SA node, is a patch of tissue in the upper part of the right atrium that triggers the heart beat. The node is sometimes known as the pacemaker of the heart.
In a normal heartbeat, the SA node sends an electrical impulse through the atria, causing them to contract. The impulse reaches the atrioventricular node, or AV node, which is located at the bottom of the right atrium. The AV node then causes the contraction of the ventricles. When the ventricles contract, blood is sent out of the heart to the body.
The heart rate established by the SA node can be modified by the nervous system. Sympathetic nerves speed up the heart rate and parasympathetic nerves slow it down.
Digitalis slows the activity of the AV node, thereby slowing the contraction of the ventricles. It also increases the parasympathic nerve stimulation of the SA node, which slows the contraction of the heart as a whole.
Although digitalis is often prescribed to increase the strength of the heartbeat, some doctors today prefer to use other medications instead of or in addition to digitalis to treat atrial fibrillation.
Digitalis can be an extremely useful medicine for heart problems, but it can also be very toxic. It can save lives or end them, depending on its dose. The difference between an effective digitalis dose and a harmful one is quite small. Therefore anyone taking digitalis needs to be monitored by a doctor.
A patient doesn’t need to be afraid of taking digitalis if their doctor prescribes it. The medication could be a wonderful help for the person’s heart problems. However, because of the possibility of side effects and of interactions with other medications, it’s essential that digitalis is taken with a doctor’s guidance.
One example of a possible digitalis complication is related to the use of diuretics and the amount of potassium in the body. Since digitalis interferes with the action of the sodium-potassium pump, it reduces the amount of potassium that enters cells. People with congestive heart failure often take a diuretic medication, which increases fluid loss from the body in urine. Potassium may be excreted in the urine, further reducing the level of potassium in the body. A doctor may prescribe a potassium supplement or a potassium-sparing diuretic in this situation. Potassium-sparing diuretics increase water loss in urine but not potassium loss.
The following symptoms could be due to digitalis toxicity, although they could arise due to other causes as well. Anyone taking digitalis should pay close attention to these symptoms.
- stomach upset
- nausea and vomiting
- loss of appetite
More serious changes may include:
- vision changes (such as blurred vision, blind spots, and changes in colour perception)
- irregular breathing
- heart palpitations
- irregular heartbeat
For many people, digitalis toxicity will never be a problem. If foxgloves are admired but not eaten and if medication instructions are followed carefully, the plant can be appreciated for both its beauty and its health benefits. It’s important that anyone involved with foxgloves or digitalis remains vigilant and watches for harmful effects, however.
Information about William Withering from the Linda Hall Library
Digitalis purpurea facts from the Royal Horticultural Society
Foxglove information from WebMD
Facts about treating heart disease with digoxin from WebMD
Digitalis medicine information from the Texas Heart Institute
Effect of digitalis-like factors on NCX from the National Institutes of Health