To compare the pharmacokinetics of
d-tubocurarine and
metocurine in man, concentrations of 3H-d-tubocurarine and 14C-metocurine (0,0,N-trimethyl-tubocurarine) in plasma, urine and bile were determined after
intravenous administration of
d-tubocurarine, 0.15 mg/kg (five patients), and
metocurine, 0.05 mg/kg (five patients), in patients anesthetized with
thiopental and
nitrous oxide for
cholecystectomy. Plasma disappearances of both drugs were triexponential, with mean terminal half-lives of 346 and 217 min for
d-tubocurarine and
metocurine, respectively. By ion-pair thin-layer chromatography, no metabolite of either compound was found in urine or bile. Renal excretions 48 hours after injection ranged from 46 to 95 per cent of the dose for
d-tubocurarine and from 46 to 58 per cent for
metocurine. Mean total-body clearances were 56 and 96 ml/min for
d-tubocurarine and
metocurine, respectively. Biliary elimination of
d-tubocurarine was greater than that of
metocurine: within 48 hours 11.8 and 2.1 per cent of the doses were excreted in bile, respectively. The observed differences in total-body clearances and volumes of distribution (V1) may be partly explained by greater protein binding of
d-tubocurarine. The results indicate that biliary excretion is an alternative route of elimination for
d-tubocurarine only. Also,
d-tubocurarine is less dependent on renal excretion for its elimination, and probably is preferable to
metocurine for use in patients with
renal failure.