Bioavailability of etilefrine from Thomasin and Thomasin sustained-release tablets

In 6 healthy volunteers absorption and elimination of etilefrine were studied in cross-over after intake of 20 mg each of a solution (A) and tablet (B) (Thomasin) or after intake of 25 mg as a sustained-release tablet (C; Thomasin retard). Etilefrine and its sulfoconjugate were measured by the GC technique in plasma and urine. From the data obtained the AUC-(plasma) and CUE-values (urine) were calculated. Peak plasma levels of 10 to 25 (A) and 6 to 13 ng . ml-1 were observed 30 min after intake. The concentrations decreased to the lower detection limit (less than 2 ng . ml-1) 2 h after intake. Plasma peak levels of 5 ng . ml-1 were measured 1-2 h after intake of the sustained-release form (C). The etilefrine plasma level decreased more slightly (C) than after intake of the other formulations (A, B). The etilefrine conjugate reached plasma peak concentrations of 600 ng . ml-1 1 h (A, B) or 2 h (C) after intake. A mean bioavailability of 70 and 58 per cent (Thomasin) or of 78 and 108 per cent (Thomasin retard) was calculated by comparison of the corresponding AUC- and CUE-values of the total etilefrine.