What? Taking digoxin can cause poisoning?

Uncle Wang has been taking digoxin for a long time to treat chronic heart failure, but he always feels loss of appetite and nausea during this period. He thought it was gastrointestinal dysfunction caused by unclean diet, but he didn't expect that when he went to see the doctor, the doctor said: "Uncle, I suspect you are poisoned by digoxin, this may be a poisoning reaction!"

"Ah? Can digoxin cause poisoning?" Two hours later, the test results came out. Uncle Wang's digoxin blood concentration was 4.25ng/mL (normal range: 0.5-2.0 ng/mL). He was really "poisoned." Uncle Wang was puzzled: "I have been taking this medicine for a long time and I have never heard of it causing poisoning! What is going on?"

Classic "old drug" digoxin

Digoxin is a commonly used cardiac glycoside drug in clinical practice. It has a positive inotropic effect, can slow down the heart rate, and effectively improve the symptoms of heart failure and cardiac function. It is widely used in the clinical treatment of heart failure and arrhythmias.

As a member of the digitalis class of drugs, digoxin has a long history. Half a century ago, it was a well-deserved star. It can be found everywhere in ischemic cardiomyopathy, dilated cardiomyopathy, heart failure, atrial fibrillation, etc. Although some new drugs have gradually replaced its position since the 1980s, digoxin is still widely used in the treatment of heart failure, atrial fibrillation and other fields. The 2017 China Heart Failure Patient Registry Study (China.HF) showed that the use rate of intravenous digitalis drugs in hospitalized heart failure patients in my country was 20.6%; the 2019 China Atrial Fibrillation (AF) Registry Study showed that the proportion of hospitalized atrial fibrillation patients in my country using digitalis drugs was 11%. In addition, it is clearly stated in the "2019 Guidelines for Rational Use of Heart Failure Drugs (2nd Edition)" that digoxin is still a recommended drug in stage C of chronic heart failure with reduced ejection fraction. Meta-analysis shows that long-term use of digoxin in patients with heart failure has a neutral effect on mortality, but can reduce their risk of hospitalization.

Be alert to poisoning reactions

Digoxin varies greatly from person to person, and its absorption and metabolism are different in each person's body. In addition, the effective dose and the toxic dose in the body are very close, so it is listed as a high-alert drug. Simply put, some people may need to use 2 tablets to see results, while others may be poisoned after using half a tablet. Poisoning reactions include loss of appetite, nausea and vomiting, diarrhea, dizziness and weakness, drowsiness, rash, blurred vision or "color vision" (yellow vision, green vision), ventricular premature beats... Once the above symptoms appear while taking digoxin, you should be alert to whether you are poisoned and go to the hospital for examination as soon as possible. If poisoning is confirmed, necessary treatment should be carried out.

Unfortunately, many patients are not well aware of the fact that digoxin can cause toxic reactions, and they are not vigilant. According to data from Henan Provincial People's Hospital, in 2021, the hospital monitored digoxin 1,038 times, of which 331 times (31.9%) reached toxic doses. Among these 331 patients, 222 (67.1%) were aged ≥60 years, and among these 222 patients, only 5 of them monitored themselves and took the initiative to come to the outpatient clinic!

Blood drug concentration is important

So, is there any way to prevent digoxin poisoning?

Yes! That is - blood drug concentration monitoring. Digoxin blood drug concentration monitoring is an important method to adjust the dosing regimen, maintain effective blood drug concentration and prevent drug poisoning.

The following points should be noted when monitoring blood drug concentrations:

1

Blood drug concentration monitoring is required when taking the drug for the first time or when changing the dosage or switching to a different manufacturer. Generally, monitoring is performed after taking the drug on time and in the right dosage for 7 consecutive days, because digoxin takes about 7 days to reach a steady-state concentration in the body.

2

It is imperative to monitor blood drug concentrations in a timely and regular manner. After taking digoxin, it is not enough to monitor once, but any changes in internal or external conditions (such as changes in weight, changes in eating habits, addition or reduction of combined drugs, suspected poisoning, etc.) must be monitored in a timely manner in order to better observe the efficacy and adjust the dosage.

3

If the monitoring results show digoxin poisoning, the drug should be stopped immediately and medical treatment should be sought, and continuous monitoring should be performed. Especially for elderly patients with slow metabolism, some patients may still have high blood drug concentrations after one week of discontinuation of treatment. Therefore, continuous monitoring is very necessary.

When taking digoxin, be sure to read the drug instructions in detail to eliminate hidden risks. For example, patients with hypokalemia, or those taking potassium-excreting diuretics (such as furosemide); patients with hypercalcemia, or those using calcium injections; patients with hypothyroidism; patients with renal impairment should use digoxin with caution. Elderly patients who take multiple drugs at the same time should also tell their doctors which drugs they are taking, and the doctor will determine whether there are drug interactions.

In short, only by paying extra attention when using digoxin can we avoid various risks, maximize its therapeutic effect, and prevent the "good medicine" from turning into "poison."

Author: Wang Yimeng, Chief Pharmacist, Pharmacy Department, Henan Provincial People's Hospital

Review expert: Ma Ailing, deputy director and pharmacist of the Pharmacy Department of Henan Provincial People's Hospital

Cheng Xiaojun, chief pharmacist of Yuncheng Central Hospital, Shanxi Province