Pharmacokinetics of Beta‐Methyldigoxin in Subjects with Normal and Impaired Renal Function

Abstract

Beta-methyldigoxin (beta-MD) was administered orally (0.2 mg) to 24 patients with various degrees of renal function, to investigate its pharmacokinetic characteristics related to renal function. Serum and urine collected until 120 hours after dosing were assayed for beta-MD and digoxin by high-performance liquid chromatography and fluorescence polarization immunoassay method. The steady-state volume of distribution decreased proportionately as creatinine clearance (CLCR) decreased, although steady-state volume of distribution of hemodialysis patients had large interindividual variability, and their mean value was not different from that of patients with normal renal function. Both renal clearance of beta-MD and digoxin were significantly correlated with CLCR (r = .820, P < .001 and r = .822, P < .01, respectively), and the slope of regression line for beta-MD was only 44% that for digoxin. Significantly reduced urinary excretion of total drug (beta-MD plus digoxin) was shown in patients with CLCR below 50 mL/minute/1.48 m2. This study suggests that the dosage modification is not necessary until CLCR decreases to below 50 mL/minute/1.48 m2, but careful attention should be given in the use of beta-MD in patients with CLCR below this value.

Role of Organic Anion Transporting Polypeptide 2 in Pharmacokinetics of Digoxin and β-Methyldigoxin in Rats

“…On one hand, there is a species difference in elimination pathways of digoxin and β‐methyldigoxin between rats and humans. For example, more than 30% of dose of these cardiac glycosides is recovered in urine within 24 h in humans 41–43. Thus, there may be some differences in the extent of hepatic distribution of these cardiac glycosides between rats and humans, although digoxin is recognized by human OATP8 (SLC21A8) and OATP8 is localized to the sinusoidal membrane of hepatocytes in humans, as well as in rats 44,45.…”