Comparison of Steady-State Serum Concentrations of Digoxin in Tablets (Lanoxin) and Capsules (Lanoxicaps) in the Elderly

Abstract

The bioavailability of digoxin in solution (Lanoxicaps, 90–100 percent) is superior to that of Lanoxin tablets (60–80 percent) in young healthy volunteers. The alleged bioequivalence of digoxin in tablets (Lanoxin 0.25, 0.125 mg) and capsules (Lanoxicaps 0.2, 0.1 mg) was studied in 20 elderly inpatients (14 women, 6 men, aged 84 ± 5 years), treated with digoxin for atrial fibrillation. In a crossover design, steady-state digoxin concentrations were measured in 16 patients after once-daily administration of Lanoxin 0.125 mg or Lanoxicaps 0.1 mg, each for at least ten days. Four other patients took Lanoxin 0.25 mg and Lanoxicaps 0.2 mg successively. The steady-state digoxin concentrations were statistically significantly different, being 1.3 ± 0.5 nmol/L for Lanoxin and 0.9 ± 0.4 nmol/L for Lanoxicaps (p=0.003). Whereas in young healthy volunteers the bioavailability of digoxin from Lanoxicaps (90–100 percent) exceeds that from Lanoxin (80 percent), in elderly patients the absorption appears to be similar. This suggests a lower than expected bioavailability of Lanoxicaps, which may result in subtherapeutic serum concentrations.