Which of the following clients is at risk for developing digoxin toxicity?

There are no evidence-based guidelines for the management of mild to moderate toxicity so there is a wide variation in treatment.13 Severe toxicity requires hospital admission and consideration of the need for digoxin-specific antibody fragments. Although digoxin-specific antibody fragments are safe and effective, randomised trials have not been performed.

The antibody fragments form complexes with the digoxin molecules. These complexes are then excreted in the urine.

Indications for digoxin-specific antibody fragments

The indications for digoxin-specific antibody fragments are inconsistent. Four contemporary sources1,9,14,15 recommend administration for strongly suspected or known digoxin toxicity with:

  • life-threatening arrhythmia
  • cardiac arrest
  • potassium >5.0 mmol/L (significant hyperkalaemia is a strong indication for treatment because of its association with a poor prognosis if digoxin-specific antibody fragments are not given16).

However, the same sources vary in their recommendations for administration when there is:

  • acute ingestion of >10 mg in adults or >4 mg in children
  • evidence of end-organ dysfunction
  • moderate to severe gastrointestinal symptoms
  • serum digoxin concentration >12 nanogram/mL
  • significant clinical features of digoxin toxicity with serum digoxin concentration >1.6 nanogram/mL.

Such disagreements over when to use digoxin-specific antibody fragments arise from cost–benefit, not harm–benefit, considerations. The cost is roughly $1000 per ampoule and several ampoules may be used. However, economic arguments have been made for their use in non-life-threatening toxicity, as the duration of hospitalisation may be reduced.17

Dose and administration

Only one formulation is available in Australia. Each ampoule contains 40 mg of powdered digoxin-specific antibody and is reconstituted with 4 mL of water. This can be given as a slow push in cardiac arrest, but otherwise the total dose is diluted further with normal saline and infused over 30 minutes.

The response begins about 20 minutes (range 0–60 min) after administration. A complete response occurs in 90 minutes (range 30–360 min).14

Conventional dosing protocols aim to neutralise total body digoxin completely. The total dose is usually expressed in vials. It depends on whether the post-distribution serum digoxin concentration is known, the amount ingested is known, or neither is known.15

Known digoxin concentration

If the post-distribution concentration is known (in either acute or chronic ingestion), knowing the amount ingested is unnecessary. The dose is:

number of vials = post-distribution serum digoxin concentration (nanogram/mL) x weight (kg)/100
(multiply by 0.78 if SI units are used for post-distribution serum digoxin concentration).

Known amount ingested

If the quantity of digoxin ingested is known, but the post-distribution serum digoxin concentration is unknown, the dose is:

number of vials = amount ingested (mg) x 2 x 0.7
(0.7 is the bioavailability of digoxin tablets supplied in Australia).

Unknown data

When neither the post-distribution serum digoxin concentration nor the amount ingested is known, use empiric dosing. Repeat in 30 minutes if the response is inadequate. The dose is:

  • for adults and children greater than 20 kg
    • five vials if haemodynamically stable
    • 10 vials if unstable
  • for children less than 20 kg

Other regimens

Some authors have argued for modification of the calculated doses to be given as an initial half dose followed by either further doses as required18 or an infusion.19 These suggestions follow from the view that full dosing is unnecessary to achieve tolerable concentrations of digoxin and may be undesirable in patients who need digoxin.18,20 There are also concerns that significant amounts of digoxin-specific antibody fragments may be eliminated before full removal of digoxin from tissue stores.19 Furthermore, in practice many hospitals will not stock sufficient ampoules for the full calculated dose. In this case specialist toxicological advice should be sought on the adequacy of modified dosing.

You can review additional information regarding these answers in the corresponding section in which the Critical Thinking activities appear.

Critical Thinking Activity Section 6.7a

1. A nurse should assess the apical pulse for a full minute before administering digoxin due to its positive inotropic action (it increases contractility, stroke volume, and, thus, cardiac output), negative chronotropic action (it decreases heart rate), and negative dromotropic action (it decreases electrical conduction of the cardiac cells).  These actions can lead to bradycardia.  If the patient’s heart rate is less than 60 beats per minute, the nurse should notify the provider before administering digoxin unless other parameters are provided.

2.The nurse evaluates the effectiveness of digoxin based on the patient’s blood pressure, apical pulse, and decreased symptoms of heart failure for which it is indicated.

3.The nurse should monitor the patient’s serum potassium level because a decreased potassium level places the patient at increased risk of digoxin toxicity.  Normal potassium level is 3.5 to 5.0 mEq/L, and a result less than 3.5 should be immediately reported to the provider due the the risk for sudden dysrhythmias. Serum digoxin levels should also be monitored, with a normal therapeutic range being 0.8 to 2 ng/mL.

4.The nurse should assess the patient’s apical pulse and  withhold the administration of digoxin.  The nurse should also check for current lab results related to the serum digoxin and potassium levels.  The nurse should notify the provider of the patient’s change in condition that could indicate digoxin toxicity and provide information regarding the patient’s apical pulse and recent digoxin and potassium levels. An order for a serum digoxin level may be received from the provider. Based on the serum digoxin level, the patient may receive a new order for digibind.  Digibind is used to treat digoxin toxicity.

Critical Thinking Activity Section 6.8

The nurse should monitor the patient’s blood pressure and heart rate.  After 5 minutes, the pain level should be reassessed and a second dose of nitroglycerin administered if the patient’s chest pain continues.  If there is no improvement in chest pain, emergency services should be obtained by calling 911 or the rapid response team.

Critical Thinking Activity Section 6.9

1.Before administering a diuretic, the nurse should assess blood pressure, the daily weight trend, serum potassium and other electrolyte levels, hydration status including 24-hour input/output, and current renal function.

2.Signs of toxicity include blurred vision, nausea, and visual impairment (such as seeing green and yellow halos). A low potassium level can increase the risk of digoxin toxicity. If a patient has digoxin toxicity, severe bradycardia and even death can occur if not treated promptly. The normal range for serum potassium is 3.5-5.0 mEq/L.

3.Furosemide (Lasix) is a loop diuretic.

4.Patients receiving loop diuretics are at high risk of dehydration.  Loop diuretics work in the loop of Henle where a great deal of sodium and water are either reabsorbed or eliminated by the kidney tubules.

5.The nurse should assess for the development of dehydration in patients receiving diuretics by monitoring  skin and mucus membranes for dryness, blood pressure for hypotension, heart rate for tachycardia, decreased urine output, concentrated urine, and increased serum sodium levels.

6.All electrolyte levels can be decreased in patients taking loop diuretics, but potassium in particular is at high risk for depletion due to the rapid water loss that occurs.

7.Furosemide can deplete potassium levels, which then increases the risk for developing digoxin toxicity.

Critical Thinking Activity Section 6.10

1.Metoprolol is a selective Beta-1 blocker that decreases the heart rate and force of contraction to reduce blood pressure.  Lisinopril is an ACE inhibitor that reduces blood pressure through vasodilation and reduces fluid retention. Verapamil is a calcium channel blocker that causes vasodilation to reduce blood pressure. Hydrochlorothiazide is a thiazide diuretic that reduces fluid retention.  For this patient, all four medications may be required to maintain a blood pressure within normal range.

2.The nurse should explain that each medication works in different ways within the body to treat high blood pressure.  It is vital to explain the importance of maintaining blood pressure within normal range to prevent additional complications such as a heart attack, heart failure, stroke, and kidney failure.

Critical Thinking Activity Section 6.12

1.Warfarin will not dissolve the existing clot, but it will help prevent additional clot formation.

2.When a patient is taking warfarin, the nurse should closely monitor INR and PT levels to verify they are in normal range to prevent bleeding complications. Specifically, the  therapeutic range for INR is between 2.0 to 3.5 depending upon the indication.

3.Dietary instructions should be provided to maintain a consistent intake of foods high in vitamin K like leafy green vegetables.  Daily changes in intake of foods that are high in vitamin K will influence the effectiveness of warfarin, as well as the patient’s INR levels used to maintain the warfarin levels in therapeutic range.

4.Patient education should emphasize bleeding precautions, avoidance of NSAIDs and aspirin, the need for routine therapeutic monitoring, and when to call the provider with signs of increased bleeding or clotting.

What puts you at risk for digoxin toxicity?

A low level of potassium in the body can increase the risk of digitalis toxicity. Digitalis toxicity may also develop in people who take digoxin and have a low level of magnesium in their body.

What is the main toxicity of digoxin?

Digoxin toxicity can emerge during long-term therapy as well as after an overdose. It can occur even when the serum digoxin concentration is within the therapeutic range. Toxicity causes anorexia, nausea, vomiting and neurological symptoms. It can also trigger fatal arrhythmias.