Anaesthetic properties of pregnanolone emulsion. A comparison with alphaxolone/alphadolone, propofol, thiopentone and midazolam in a rat model.

The anaesthetic properties of pregnanolone emulsion, a new steroid preparation for intravenous administration, were evaluated in rats and compared to those of Althesin, propofol, thiopentone and midazolam. The therapeutic index was found to be 50% higher than that of Althesin and 6-8 times higher than those of propofol, thiopentone and midazolam. Induction with pregnanolone emulsion was reliable and fast, with only minor excitatory side effects, although induction time was longer compared to Althesin, propofol and thiopentone. Movement of unstimulated rats during sleep was similar to that seen with Althesin but movement on painful stimulation was less than with propofol and thiopentone. Recovery was rapid and smooth, and the proportion of sleeping time to recovery time was higher than found for the other four anaesthetics. No cumulative effects were seen on repeated administration and there were no venous sequelae. The results indicate that pregnanolone emulsion may provide a short-acting, less cumulative and less toxic alternative to existing intravenous anaesthetic agents.