Infusions of minaxolone to supplement nitrous oxide-oxygen anaesthesia. A comparison with althesin

Development of pharmacophoric maps for cardiovascular depression by intravenous anaesthetic agents: comparison with maps for immobilizing activity

BACKGROUND

The molecular basis of the cardiovascular effects of i.v. anaesthetics was investigated using comparative molecular field analysis (CoMFA).

METHODS

The cardiovascular effects, measured as changes in mean arterial pressure (MAP), compared with awake values of continuous infusions of 13 structurally diverse i.v. anaesthetics were compared at EC(50) plasma concentrations, and by determination of plasma-free drug concentrations associated with a 20% decrease in MAP (dMAP(20)). Data were obtained both from the literature and from unpublished data of the author. The results were fitted to a CoMFA activity model using field-fit minimization techniques to maximize similarities in molecular bulk and electrostatic potential to the lead compound, eltanolone.

RESULTS

The final model for cardiovascular depression based on free drug concentrations associated with dMAP(20) explained 95.8% of the variance in observed activities, with a cross-validated q(2) of 0.824 (n=12). A second model based on change in MAP at EC(50) plasma concentrations explained 98.3% of the variance in arterial pressure, but performed poorly at cross-validation (q(2) 0.526). The comparative model for immobilizing potency had an r(2) value of 0.987 and q(2) 0.823. Comparison of pharmacophoric maps showed several key electrostatic and steric regions common to both models when isocontours were constructed linking lattice grid points, making the greatest 40% contributions (87.57% for electrostatic fields and 86.16% for steric fields).

CONCLUSIONS

Comparison of activity models for cardiovascular depression and immobilizing potency for i.v. anaesthetics shows significant commonality, suggesting that it may not be possible to separate those molecular features associated with each of these effects.

What makes a molecule an anaesthetic? Studies on the mechanisms of anaesthesia using a physicochemical approach

Recent studies of mechanisms of anaesthesia have been mainly 'target orientated', investigating the activity of both volatile and i.v. agents at putative sites of action. An alternative approach is one that is 'ligand orientated', focusing on the properties of molecules that define their immobilizing ability and secondly define their potency. The use of conventional descriptors (such as non-polar solubility or the octanol-water partition coefficient [Log P]) are limited in their utility as predictors of potency as they represent three-dimensional molecular properties as a one-dimensional parameter. Using different computer-based molecular modelling methods (molecular similarity studies and comparative molecular field analysis [CoMFA]), we have identified the molecular bases of the activity of structurally diverse anaesthetics, such that they can be described as a single model based on the spatial distribution of molecular bulk and electrostatic potential. The same approach can also be used to model other properties of anaesthetic agents, such as cardiovascular depression. The present data suggest that, for the i.v. agents, it may be difficult to separate immobilizing (anaesthetic) activity and cardiovascular depression within a single molecule.

Can molecular similarity-activity models for intravenous general anaesthetics help explain their mechanism of action?

BACKGROUND

The importance of molecular shape and electrostatic potential in determining the activities of 11 structurally-diverse i.v. general anaesthetics was investigated using computational chemistry techniques.

METHODS

The free plasma anaesthetic concentrations that abolished the response to noxious stimulation were obtained from the literature. The similarities in the molecular shapes and electrostatic potentials of the agents to eltanolone (the most potent anaesthetic agent in the group) were calculated using Carbo indices, and correlated with in vivo potency.

RESULTS

The best model obtained was based on the similarities of the anaesthetics to two eltanolone conformers (r2=0.820). This model correctly predicted the potencies of the R- and S-enantiomers of ketamine, but identified alphaxalone as an outlier. Exclusion of alphaxalone substantially improved the activity correlation (r2=0.972). A bench mark model based on octanol/water partition coefficients (r2=0.647) failed to predict the potency order of the ketamine enantiomers.

CONCLUSIONS

The results demonstrate that a single activity model can be formulated for chiral and non-chiral i.v. anaesthetic agents using molecular similarity indices.

Hemodynamic effects during induction, laryngoscopy, and intubation with eltanolone (5 beta-pregnanolone) or propofol. A study in ASA I and II patients

STUDY OBJECTIVE

To evaluate the cardiovascular changes following induction of anesthesia, laryngoscopy, and intubation in patients receiving a bolus dose of either eltanolone or propofol.

DESIGN

Randomized, controlled, blind, prospective clinical study.

SETTING

General operating theaters of a university hospital.

PATIENTS

40 ASA status I and II patients scheduled for elective surgery.

INTERVENTIONS

Patients were premedicated with oral temazepam 20 mg. Anesthesia was induced with either eltanolone 0.58 mg/kg or propofol 1.7 mg/kg, neuromuscular blockade was achieved with vecuronium 0.1 mg/kg, and anesthesia was maintained with enflurane 0.5% to 1.0% in nitrous oxide (67%).

MEASUREMENTS AND MAIN RESULTS

Blood pressure was measured using an automatic oscillometric technique, heart rate (HR) was derived from the ECG, oxygen saturation was measured by pulse oximetry, and cardiac output (Q) was measured by a thoracic bioimpedance technique. Induction of anesthesia with either drug, eltanolone or propofol, decreased arterial systolic (SAP) and diastolic (DAP) blood pressure, Q, and stroke volume (SV). HR increased. Systemic vascular resistance (SVR) was unaltered. After laryngoscopy and intubation, SAP and DAP increased secondary to an increase in SVR. HR also increased; SV decreased in patients receiving eltanolone. Side effects (e.g., apnea occurring for more than 30 seconds, involuntary movements, limb hypertonus) occurred at a similar incidence with both treatments, but pain following injection was greater with propofol (59% vs. 9%).

CONCLUSIONS

Patients receiving either eltanolone or propofol showed similar cardiovascular changes to induction of anesthesia, although there were greater increases in arterial pressure and HR in those patients receiving eltanolone.

General kinetic and dynamic principles and their application to continuous infusion anaesthesia

The use of intravenous anaesthetic agents by continuous infusion requires knowledge of their pharmacokinetic properties. In this article, the general pharmacokinetic principles behind the use of infusions of intravenous agents are presented and the literature with regard to the individual drugs used in this way is reviewed.