Cardiac arrhythmias, electrolytes, and digoxin concentration in plasma and urine in patients treated with digoxin

Cardiac arrhythmias, digoxin concentration in plasma and urine, digoxin and creatine clearances, electrolytes in plasma and in erythrocytes, and subjective symptoms have been carefully studied for 5 consecutive days in 19 patients with definite or suspected digitalis intoxication. The digoxin treatment was discontinued during the observation period. Eleven controls without any signs of toxicity were similarly followed on unchanged maintenance dosage. All patients were independently classified as toxic or non-toxic from the follow-up of extended ECG recordings and subjective symptoms. In 9 definitely toxic patients a plasma digoxin concentration 3.1 plus or minus 0.7 ng/ml was found, as compared to 1.4 plus or minus 0.5 ng/ml for the 11 controls. In the suspect toxic group 1.5-3.9 ng/ml was found. The high digoxin level in the toxic group corresponds to a low digoxin clearance. In the toxic patients cardiac arrhythmias were related in most cases to a plasma digoxin level above 2.5 ng/ml and usually disappeared when the concentration had decreased below this. Suspect toxic patients, classified as probably non-toxic, and controls had with two exceptions plasma digoxin levels below 2 ng/ml. It is suggested that digitalis toxicity should be considered at a plasma digoxin concentration above 2 ng/ml. It must be stressed that this limit is not absolute and is affected by, among other things, a disturbance of intra- and extracellular electrolytes.