Study of serum digoxin status in digitoxicity by radioimmunoassay

Forty-seven patients who were being treated with digoxin in a daily dose range of 0.25 mg. to 0.75 mg. were the study material. Thirty-two patients were toxic. Seven patients out of these 32 were in an under-digitalized state and 15 patients were nontoxic. All patients were clinically assessed and investigated for routine hematological value, serum protein, electrolytes, serum creatinine, blood urea, and serum calcium.Serum digoxin concentration was estimated in all cases by the radioimmunoassay method. The assay was repeated after the patients recovered from toxic manifestations on withdrawal of the digoxin. The mean serum digoxin level in toxic patients (2.64 ± 0.68 ng./ml.) was significantly higher (P < 0.001) than that in nontoxic patients (1.35 ± 0.45 ng./ml.). After recovery from toxicity, the mean serum digoxin level (1.43 ± 0.32 ng./ml.) was found to be significantly lower than the level in the toxic patients and was similar to the level in patients of the nontoxic group. Seven patients whose symptoms simulated digitoxicity were in fact in an under-digitalized state (0.74 ± 0.35 ng./ml.), and their symptoms were relieved with a higher dosage of digoxin. In this study an attempt has been made to show the importance of the estimation of serum digoxin in the assessment of therapeutic and toxic effects of the drug so as to modify the dosage schedule for the optimal therapeutic response.