[Development of proxibarbal blood levels. The role of various elimination processes]

Half-lives of barbiturates are short when their lipid solubility is high but long when they are less lipophilic. Infection of radiolabelled proxibarbal to rats, and analysis of their blood by thin-layer chromatography shows that this compound, though highly hydrophilic has a short half-life of elimination (51 mn). Neither hepatic oxidation nor tissular distribution are important (different from lipophilic compounds). Valofan formation plays a role in the decrease of barbiturate-alcohol concentration. When equilibrium between proxibarbal and valofan is established, it does not influence any more the elimination rate. It explains that the apparent half-life of these two compounds are similar. Tubular reabsorption is stopped by the highly hydrophilic character of proxibarbal (different from medium lipophilic compounds) and elimination by kidney is the main process and explains the shortness of half-life.