Digoxin
At a Glance
Why Get Tested?
To determine if the concentration of digoxin in your blood is at a therapeutic level or to detect toxic levels
When to Get Tested?
At least one week after the start of digoxin therapy and at regular intervals to ensure that drug levels are within therapeutic range and are not low or at toxic concentrations
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
No special test preparation required but the sample is usually drawn not long before the next dose is due (this is called a trough level).
The Test Sample
What is being tested?
Digoxin is a drug used to treat heart failure and abnormal heart rhythms. This test measures the amount of digoxin in the blood. Heart failure, including congestive heart failure (CHF), causes the heart to become less effective at circulating blood. As a result, blood backs up into the legs, hands, feet, lungs and liver, causing swelling, shortness of breath and fatigue.
Digoxin is prescribed to alleviate some symptoms of heart failure. It strengthens the contractions of the heart and helps it to pump blood more efficiently. Digoxin also helps control the heart rate and abnormal heart rhythms known as arrhythmias. It will not cure heart failure or arrhythmias, which are chronic conditions, but can help to manage the symptoms along with diet, exercise, and other medications.
Digoxin levels need to be monitored because digoxin is a drug that has a narrow safety range. If the level in the blood is too low, symptoms may recur. If the level is too high, toxicity may occur with possible side effects such as:
- dizziness
- blurred vision or seeing yellow or green halos
- vomiting
- diarrhoea
- irregular heartbeat, or
- difficulty breathing.
Digoxin dosage may be adjusted based on levels measured.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No special preparation is needed, but timing of the sample for testing is important. The sample should be drawn at least 6-8 hours after the last dose.
The Test
How is it used?
A digoxin test is ordered by your doctor to monitor the level of drug in your blood. The dose of digoxin prescribed by your doctor may be adjusted depending on the level measured. Your doctor will want to monitor the level of digoxin at regular intervals to ensure that a therapeutic level is maintained and that toxic levels have not been reached and will not produce symptoms of toxicity.
When is it requested?
The test to measure digoxin is ordered at the beginning of drug therapy to ensure correct dosage. Digoxin takes approximately one to two weeks to reach a steady level in the blood and in the target organ, the heart. A test done at that time will reflect more accurately whether you are receiving the right amount of digoxin. Digoxin levels are monitored routinely at a frequency determined by your doctor after that to verify correct dosage or if any changes occur in drug source, dosage, or other medications taken at the same time. Changes in your health status can also affect levels of digoxin and its ability to control your symptoms. Some physiological changes that may affect levels of digoxin in the blood are:
- kidney function
- thyroid problems
- cancer
- stomach or intestinal illness
Digoxin will not cure heart failure but will help to control it. Since digoxin is prescribed to treat patients with a long-term, chronic condition, it is usually monitored throughout the patient’s lifetime.
Timing of the digoxin blood test is important. The sample should be drawn at least 6-8 hours after the last dose. Many times, the blood sample will be drawn just before the next dose is to be taken. Timing of the sample collection is important because if the sample is drawn too soon after dose, the results of the test may be erroneously high and will show a toxic level when that is not the case.
What does the test result mean?
The therapeutic range for digoxin has been established over time as 0.5-2.0 µg/L. Several new studies suggest a more narrow range, 0.5-1.0 µg/L, may be appropriate for patients with heart failure. The recommended range for patients with arrhythmias is 0.5-2.0 µg/L. Most patients find that their symptoms improve when their digoxin levels are within these ranges.
It is important to note that each patient’s response to medications is individual and other factors such as kidney function or concurrent medications may be involved. If your symptoms have not improved or if you are experiencing side effects, tell your doctor immediately. He or she may need to adjust your dose according to your individual needs.
If your result does not fall within the therapeutic range but you are not experiencing symptoms, continue to take your medication as prescribed until you consult with the doctor who ordered the test. They will evaluate your case and decide if it is necessary to adjust your dose. If your dose needs to be adjusted, your doctor may order additional digoxin tests to determine the resulting blood level.
Is there anything else I should know?
Several prescribed and over-the-counter drugs can affect the level and effectiveness of digoxin in your system. Be sure to tell your doctor about other medications you may be taking.
Digoxin is primarily cleared from your system by the kidneys. Tell your doctor if you have or have had known kidney problems. Your doctor may want to monitor blood potassium levels since low levels of potassium can result in symptoms of toxicity.
In cases where toxic levels of digoxin are measured, antidigoxin antisera may be administered to reverse the effects of the drug.
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