As outlined earlier, digoxin causes an increase in the force of contraction of the heart muscle and slows the heart rate, especially in patients who have atrial fibrillation. It is excreted virtually unchanged by the kidney. Therefore, in kidney dysfunction or failure, the drug accumulates and can reach toxic levels in the body. Patients with poor kidney function may therefore require 0.125 mg daily or every other day.
1. Advice and Adverse Effects
Kidney dysfunction or failure is the most common cause for toxicity. Note that individuals over age 70 may have kidney blood tests (for creatinine) that are recorded as normal when the kidney function is abnormal. The doctor therefore has to titrate the dose carefully in the elderly to avoid toxicity.
Nausea and vomiting are common symptoms of excess digoxin in the blood. Blue-green-yellow vision may occur but reverts to normal as soon as the drug is stopped. A very slow heart rate, less than 48 beats per minute, with extra heartbeats and the precipitation of abnormal heart rhythms are also seen with toxic doses. If this occurs, the drug must be discontinued and levels in the blood measured. Low blood potassium increases all adverse effects, and this may occur even with a small dose of digoxin. The potassium level in the blood should be checked every four months or more frequently in some cases. Diuretics are well known to cause potassium loss, and because they are virtually always used along with digoxin to treat heart failure, digoxin toxicity may occur. This results in serious heart rhythm disturbances. Your physician will give advice on your diet and tablets or if a liquid containing potassium is required. Digoxin toxicity was common during the 1970s.

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