Cardiac glycosides are a class of steroid medications used to treat heart failure. These medications can have both positive and negative effects on the heart, kidneys, stomach, intestines, and nervous system. Medications containing cardiac glycosides work directly on the tissues of the heart. A bitter taste is typical of both naturally occurring and refined forms of this prescription steroid. Overdoses can have serious consequences, including hallucinations, allergic reactions, and an irregular heartbeat.
There are two structural features to cardiac glycosides: the sugar and the non-sugar portions. The R-group in the non-sugar portion determines the type. Cardiac glycosides are divided into two main types: bufadienolides and cardenolides. The cardenolids have an unsaturated butyrolactone ring, while the bufadienolides have an a-pyrone ring. Of the two, cardenolids are the most prolific.
Medication containing cardiac glycosides works by directly affecting the cell membranes of heart tissues. Positive inotropic action refers to the way the medication increases the pumping strength of the heart. By increasing the heart’s pumping strength, it can pump more blood through the body per heartbeat. The prescription medicines deslanoside, digitoxin, and digoxin contain cardiac glycosides and are available only from a pharmacy. These drugs may be used in the treatment of congestive heart failure, cardiac arrhythmia, and atrial fibrillation and flutter.
Plants containing cardiac glycosides include Christmas rose, the highly toxic foxglove, and lily of the valley. Such plants have been used as poisons and heart medications since at least 1,500 B.C., and their extracts still are used in some treatments. Traditional uses include arrow poisons and heart tonics. These plants also have been used as emetics, which can cause vomiting, and as diuretics, which increase the volume of urine excreted by the body.
Cardiac glycosides can be poisonous if taken in large amounts. Care should be taken in calculating dosage, because the correct therapeutic dose often is an amount close to the toxic threshold. Particular caution may be necessary when handling the plants that contain naturally occurring forms of these medications. Sucking or consuming portions of the foxglove or oleander plants can result in foxglove poisoning or oleander poisoning. These terms can also refer to overdoses of medications containing extracts from either plant. Risks generally are greatest in children and the elderly.
Symptoms of cardiac glycoside overdose vary. Those seen only in chronic cases include hallucinations, depression, loss of appetite, and seeing halos around objects. Such halos usually occur in yellow, green, or white. Other possible symptoms for both chronic and non-chronic cases include allergic reactions, blurred vision, disorientation, fainting, and headaches. Additional symptoms might include irregular heartbeat, lethargy, stomach pain, vomiting, and weakness. If an overdose is suspected, a person typically should contact emergency services immediately and not induce vomiting unless instructed to do so by poison control or a doctor.