Lipid solubility of pancuronium and vecuronium determined by n-octanol/water partitioning.

We have measured the n-octanol/water distribution coefficients at 37 degrees C of two steroidal myoneural blockers (pancuronium and vecuronium) and of their 3-hydroxy metabolites over a pH range from 1.5 to 11. Pancuronium was found not to be lipid soluble. The mean distribution coefficient of 3-hydroxy vecuronium at pH = 7.4 was 0 and that of vecuronium 0.12 (SD 0.1). Distribution coefficients of the parent drug showed a slightly greater lipid solubility than the metabolite (11.37 (2.91) and 9.53 (3.44), respectively (mean t0.05 x SE)). Because of its lipid solubility, vecuronium may penetrate into lipid structures.