Pharmacokinetics and protein binding of methocarbamol in renal insufficiency and normals

We determined plasma methocarbamol concentrations over 24 h following a 1.5 g methocarbamol dose (off-dialysis day) to 8 chronic haemodialysis patients and compared these results to those from 17 healthy male volunteers. The harmonic mean elimination half-life was similar between the two groups, 1.24 and 1.14 h, respectively. tmax and the weight-adjusted Cmax were 1.1 h and 27.0 mg.m-1 for haemodialysis patients and 1.1 and 23.1 mg.l-1 for normals. Relative systemic availability was assessed by comparing weight-normalized AUC x k10 products. These results indicate no significant differences with respect to methocarbamol absorption, with the relative systemic availability in patients being 113%. These data suggest that absorption and elimination of methocarbamol is similar between normal subjects and patients undergoing maintenance haemodialysis.