Detecting digoxin toxicity

Nursing, Dec 2000 by Newton, Janice L, Johnson, Tom W

MR. BRANNEN, 74, ARRIVES at your hospital with a slow heart rate. He takes 0.25 mg of digoxin once a day and 20 mg of furosemide twice a day for heart failure. His electrocardiogram shows atrial fibrillation, with a slow ventricular response of 42 beats/minute (bpm), depressed ST segments, a short QT interval, and flattened T waves.

Mr. Brannen reports 4 days of anorexia, nausea, vomiting, and occasional diarrhea before he sought medical attention. His wife says he'd started falling asleep frequently, looked pale, and mentioned seeing yellow halos around objects. All these signs and symptoms point to digoxin toxicity.

Recipe for toxicity

Digoxin's narrow therapeutic range (0.8 to 2 ng/ml) makes toxicity quite common: It's estimated to be present in 5% to 20% of all hospitalized patients on digoxin. Testing serum drug levels about 8 hours after each drug administration helps detect toxicity. Log and report digoxin levels greater than 2 ng/ml and a heart rate below 60 bpm; these are key indicators of digoxin toxicity, though many patients who are on digoxin routinely have heart rates below 60 bpm.

Renal insufficiency, drug interaction, hypercalcemia, hypokalemia, hypomagnesemia, hypothyroidism, and advanced age all increase the risk of digoxin toxicity. (See Raising the Risks for common drugs that can cause problems.) Gastrointestinal symptoms of toxicity include anorexia, nausea, and vomiting. Neurologic symptoms include headaches, malaise, fatigue, neuralgic pain, dementia, seeing yellow or green halos around objects, and seizures. Cardiac signs include functional rhythms, heart blocks, ventricular rhythms, acute tachycardia, and bradycardia.

Treating the problem

Treatment for digoxin toxicity depends on its severity. After Mr. Brannen's heart rate dropped into the low 30s, he was treated with a temporary transcutaneous pacemaker and given the cardiac glycoside antidote digoxin immune Fab (Digibind). This drug binds with unbound digoxin, so it's unavailable to bind with cells. After treatment with Digibind, use signs and symptoms to judge toxicity, not digoxin levels, which will remain high even though the patient may no longer be in danger.

The bottom One

Properly administered and titrated, digoxin improves cardiac output for many patients. Completely review the health history of any patient taking digoxin and intervene promptly if you suspect toxicity.

Raising the risks

These common drugs increase the risk of digoxin toxicity:

- amiodarone

- verapamil

- amphetamines

- diet pills

- propafenone

- furosemide

- hydrochlorothiazide

SELECTED REFERENCES

Marik, P, and Fromm, L.: "A Case Series of Hospitalized Patients with Elevated Digoxin Levels," American Journal of Medicine. 105(2); 110-5, August 1998.

Nursing 2001 Drug Handbook. Springhouse Corp., Springhouse, Pa., 2000.

BY JANICE L. NEWTON, RN, CNS, MS

Clinical Nurse-Manager

Post Coronary Care Unit * University Hospital * Oklahoma City, Okla.

TOM W. JOHNSON, PA-C

Instructor of Medicine

Cardiovascular Section * The University of Oklahoma * Oklahoma City, Okla.