Patient history should focus on determining the exact type and amount of medication taken and whether there has been co-ingestion of other substances. Abrupt cessation of these barbiturates while taking a beta-blocker could increase the effect of the beta-blocker or cause frank toxicity. Pentobarbital and phenobarbital have increased the clearance rate and reduced the plasma concentrations of some beta-blockers. Barbiturates easily cross the placenta and are excreted into breast milk.īarbiturates are also hepatic enzyme inducers which means that they will induce the metabolism of other medications, including other barbiturates. Phenobarbital is a long-acting, polar drug that is slowly absorbed and slowly redistributed, contributing to its longer duration of action. However, phenobarbital is only partially converted and can be found unchanged in the urine. Most are rapidly metabolized to inactive compounds before they are excreted in the urine. High lipid-solubility in some (amobarbital, pentobarbital, and thiopental) allow them to be well absorbed and rapidly redistributed. The onset of action for oral administration ranges from 20 to 60 minutes, and intravenous administration can range from almost immediate to 5 minutes. Barbiturates have various onsets of action, durations, half-lives, and toxic levels, depending on the lipid solubility and rate of metabolic inactivation.
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