Plasma half life of beta-methyl digoxin following repetitive application in man

Serum glycoside concentrations after single or repeated intravenous doses of beta-methyl-digoxin and digoxin

The aim of the present investigation was to estimate the ratio of the intravenous doses of beta-methyl-digoxin and digoxin required to produce identical serum glycoside concentrations in man. 20 patients on intravenous maintenance therapy were changed from beta-methyl-digoxin to the identical dose of digoxin or vice versa. Each drug was given for 7 days. Serum concentrations 13% higher were found during administraton of beta-methyl-digoxin. Assuming a half life of 60 h after withdrawal, the dose of digoxin producing the same minimum serum concentration was estimated to be 1.16 times higher than that of beta-methyl-digoxin. 18 healthy volunteers received 0.4 mg beta-methyl- digoxin, and 23 the same dose of digoxin, as an intravenous infusion over 2 h. The serum concentrations and urinary glycoside excretion were measured over a period of 32 hrs. During the first hour after the infusion the serum concentration of digoxin declined more rapidly than that of beeta-methyl-digoxin. Thereafter, the ratio of the serum concentrtions did not change appreciably up to the end of the investigation. The area under the serum concentration/time curve was about 13% greater for beta-methyl-digoxin than for digoxin; this difference was not significant. The average renal clearance was 96 +- 9 ml for beta-methyl-digoxin, 151 +- 13 ml for digoxin. Since the total body clearance of digoxin is only about 1.16 times higher than that of beta-methyl-digoxin, the lower renal clearance of beta-methyl-digoxin must partly be compensated by higher extrarenal clearance. From the ratios of the areas under the serum concentration/time curves after single doses of beta-methyl-digoxin and digoxin, and the minimum serum concentrations during maintenance therapy, it was concluded that the dose of digoxin to produce the same average serum concentrations would be about 1.15 times higher than that of beta-methyl-dogoxin. In comparison wtih the large variations in individual dosage of digoxin and beta-methyl-digoxin, this difference is too small to be of practical importance.

Absorption of beta-methyl-digoxin determined after a single dose and under steady state conditions

Single doses of beta-methyl-digoxin 0.4 mg were given to groups of 17-18 healthy volunteers as an intravenous infusion lasting 2 hours, or orally as Lanitop Liquidum or Lanitop tablets. The serum glycoside concentration and urinary glycoside excretion were measured over 8 and 32 h. The absolute bioavailability from the oral preparations in comparison with the infusion was lower for the first 8 h than for the entire 32 h of the investigation; the relative bioavailability from tablets was the same as from the solution for both periods. For both periods the area under the serum concentration/time curve and the urinary glycoside excretion were significantly lower after administration of the tablets than after intravenous infusion. Taking the average of both parameters, the absolute bioavailability of beta-methyl-digoxin was about 80% from the solution and about 70% from the tablets. In 18 patients undergoing intravenous or oral therapy with beta-methyl-digoxin steady state glycoside concentration were compared in a cross-over study of intravenous maintenance therapy with Lanitop ampoules or oral treatment with Lanitop tablets. For a standard daily dose of 0.2 mg beta-methyl-digoxin the serum concentrations were 1.35 +/- 0.10 ng/ml during both intravenous and oral administration. The intra-individual variation in glycoside concentration after changing from intravenous to oral maintenance therapy, or vice versa, was about the same as during continued intravenous or oral administration. It is concluded that the rate of rise of serum concentration after a single dose may be a useful indicator of the rate of absorption, but that the area under the serum concentration/time curve and the urinary glycoside excretion up to 32 h are unsuitable for determining equivalent doses of different formulations or routes of administration of digitalis glycosides.

Half-life plasma following repetitive application of beta-acetyl digoxin in man

The aim of this study was to determine the half-life of beta-acetyl digoxin in plasma after cessation of its continous oral application. 18 healthy male volunteers received 0.4 mg p.o. of beta-acetyl digoxin daily for a period of 14 days. Plasma glycoside concentrations were measured up to 108 hours after the last application utilizing a 86Rb-erythrocyte assay. Mean plasma digoxin concentration 12 hours after the alst dose was -x=1.05 ng/ml, sx=0.301. Mean half-life in plasma was 55.8 hours (sx=21.7). This corresponds to a mean daily elimination rate of abour 25.8%. These results are in good agreement with the 20% loss of effect on the heart as reported in the literature.