Antidotes for digitalis toxicity include discontinuation and observation, gastric lavage, and the use of digitalis-fab antibodies — anti-arrhythmic medications and replenishing of electrolytes can also alleviate adverse effects. Also known as digoxin, the most common source of digitalis is the foxglove plant, digitalis purpurea. The drug is used to treat heart conditions including atrial fibrillation and atrial flutter. Available in both oral and injectable forms, the normal therapeutic dose of digitalis is 0.8 to 2.0 nanograms per milliliter. Serum levels above this range result in cardiac glycoside toxicity, and it is then that antidotes for digitalis poisoning are required.
Digitalis toxicity can be either acute, when an excess of the drug is consumed in a short amount of time, or chronic, as in individuals who take medications that cause electrolyte abnormalities. For example, the use of diuretics can result in the depletion of potassium, which subsequently increases the risk of digitalis poisoning. Other risk factors include drug interactions, myocardial infarction, or ischemia. Hypothyroidism, hypercalcemia, and advanced age can also increase the risk of toxicity.
Symptoms of digitalis poisoning include irregular heart rhythms, syncope, hypotension, and fatigue. Other symptoms include vomiting and diarrhea, abdominal pain, or headache and dizziness. Some people also experience altered mental states, increased urination, and cold sweating. Swelling of the legs, altered or blurred vision, and anorexia are all also often presented. Doctors confirm a diagnosis through an electrocardiogram (ECG), digitalis levels, and potassium and magnesium levels.
The antidotes for digitalis toxicity are based on the symptoms and specific toxic effects on the patient rather than just the level of the drug in the serum as toxicity levels can vary among individuals. For patients who have chronic toxicity and are stable, treatment usually consists of discontinuing the use of the drug. Doctors keep patients hydrated and observe them until serum digoxin levels have returned to within a normal range.
Gastric lavage with activated charcoal is often used as a first-line treatment. This reduces the absorption of the digitalis and disrupts circulation of the drug through the liver. Binding resins, including cholestyramine and colestipol, can also be used for this purpose. Gastric lavage, however, can worsen arrhythmias, so doctors administer atropine first as a preventative if this technique is used.
For acute cases, initial treatment includes the use of digitalis-fab fragments. These immunoglobulin fragments bind to the digitalis, which subsequently prevents the digitalis from binding to cells in the body. The bindings form complexes in the blood, which then pass through the kidneys and are excreted. Commercial names for these fragments include Digibind and DigiFab.
Anti-arrhythmics can also treat digitalis poisoning, depending on the arrhythmia. For example, doctors choose lidocaine and phenytoin if ventricular tachycardia is presented. Electrolytes must also be balanced. In acute cases, hyperkalemia is common and is treated with sodium bicarbonate, insulin, glucose, or ion-exchange resins such as Kayexlate. For chronic toxicity, hypokalemia and hypomagnesium are more likely and are treated with intravenous infusions of magnesium sulfate and potassium in dextrose solution.
Factors involved in the choice of antidotes for digitalis poisoning include the severity of the poisoning and the symptoms presented. Age, medical history, and chronicity also play roles along with existing heart disease, renal insufficiency and changes in ECG. Other factors include electrolyte and digitalis levels. Doctors consider the etiology of the poisoning as well, for example, the dose taken, other medications that may have also been taken, and whether the poisoning was intentional or accidental.