Table. 1. Elimination Half-Life of Serum Digoxin after a Massive Overdose

394 CLINICAL CHEMISTRY, Vol. 29, No. 2, 1983 logarithmic but biphasic in nature. The biological half-life of the drug was shorter 124 h if estimated by visual inspection; 13 h if estimated by the method of residuals (1)1 during the first two days, longer (52 h) for the following three days (Figure 1). At therapeutic concentration in plasma, digoxin enters the elimination (/3) phase from the distribution (a) phase within 7 to 12 h after an oral dose (2); the mean half-life for digoxin elimination is about 1.6 days (39 h) in individuals whose renal and hepatic function is normal (3). Dungan et al. (4) reported that the half-life of digoxin in children is similar to that found in adults with normal renal function (4). We found four cases (Table 1) of suicidal or accidental digoxin poisoning in the literature in which sufficient serial determinations of serum digoxin concentrations were reported that we could assess the kinetics of elimination. Hobson and Zettner (5) reported that the half-life was longer (43 h) initially and shorter (15 h) during the following days in a 60-year-old woman who had a history of heart disease and was treated with digoxin (Case 1). They postulated that the early prolongation of serum digoxin half-life observed was the result of continued intestinal absorption of the ingested drug. From five serum digoxin values obtained during four days, Smith and Willerson (6) estimated the apparent half-lives of digoxin in the serum of a 51-year-old man being treated with digoxin to be 10 h on the first day, 21 h on the second day, and 32 h during the following two days (Case 2). Bertler et al. (7) estimated the half-lives of digoxin in serum of a 78-year-old man being treated with digoxin to be 24 h for the first two days and 60 h during the following six days (Case 3). Ahlmark (8) estimated the half-lives of serum digoxin in a 45-year-old man with no history of heart disease to be 20 h during the first two days and 33 h during the following two days (Case 4). Cardiac disease and increasing age are both associated with diminished creatinine clearance and with decreased renal and total clearance of digoxin (9). Serum creatinine or creatinine clearance was normal in Cases 1