Comparative molecular field analysis to derive pharmacophore maps for induction doses of intravenous anaesthetic agents

Quantitative analysis of thiamylal and its metabolite secobarbital using liquid chromatography-tandem mass spectrometry in adipose tissue, serum, and liver

Thiamylal is an ultrashort-acting barbiturate used for intravenous administration or general anesthesia induction. However, some cases of poisoning and suicide with thiamylal administration have been reported. Additionally, there are few reports on its analysis in the organs and adipose tissue, which requires purification by column chromatography and evaporation. A rapid and sensitive method was developed for quantifying thiamylal and its metabolite, secobarbital, in the adipose tissue, serum, and liver using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Samples were prepared using modified QuEChERS extraction. For adipose tissue samples, an acetonitrile-hexane partitioning step was added to the extraction. This method was applied to investigate a suspected self-poisoning autopsy case. The quantitation accuracy for thiamylal added to porcine pericardial fat (0.18 µg/g), human serum (0.015 µg/mL), and porcine liver (0.18 µg/g) was 103%, 113%, and 95.3%, respectively. The quantitation limits calculated for porcine pericardial fat, human serum, and porcine liver at a signal-to-noise ratio of 10 were 0.06 µg/g, 0.005 µg/mL, and 0.06 µg/g, respectively. In addition, the thiamylal and secobarbital levels in the forensic autopsy case were 140 and 1.5 µg/g, respectively, in myocardial fat; 3.5-4.9 and 0.12-0.20 µg/mL, respectively, in serum; and 6.2-42 and 0.58-1.1 µg/g, respectively, in liver tissue. Thiamylal is especially distributed in the adipose tissue. The thiamylal-to-fat ratio may help estimate the time from administration to death. The developed modified QuEChERS extraction method with acetonitrile-hexane partitioning is suitable for analyzing hydrophobic compounds, such as thiamylal, in the adipose tissue.

Comparative molecular field analysis to derive pharmacophore maps for disposition parameters of intravenous anaesthetic agents

BACKGROUND

The present study examines the molecular basis of the disposition kinetics for i.v. hypnotic agents using comparative molecular field analysis (CoMFA).

METHODS

The systemic clearance (Cl(s) litre min(-1)) and apparent volume of distribution at steady state (Vd(ss) litres) for 14 i.v. anaesthetics in human subjects were obtained from the literature, or from unpublished data, and used to form CoMFA models for the two aspects of drug disposition. Molecular alignment was achieved by field-fit minimization with the lead structure for all models eltanolone. The resulting pharmacophore maps were also compared with the pharmacophores for cardiovascular depression (expressed in terms of the drug concentration in 50% patients, associated with a 20% decrease in mean arterial pressure during infusion anaesthesia in the absence of other adjuvant drugs or noxious stimulation), which were taken from the literature.

RESULTS

The CoMFA model for Cl was based on two latent variables, explained 95.2% of the variance in observed activities, and showed good intrinsic predictability (cross-validated q(2) 0.663). The model for Vd(ss) was also based on two latent variables: r(2) 0.986 and q(2) 0.718. Comparison of the pharmacophores for the two disposition parameters showed poor correlation for both electrostatic and steric regions (r=-0.220 and 0.018; both NS). The relative contributions of electrostatic and steric interactions differed between the models (Cl(s) 1.9:1; Vd(ss) 2.5:1). Comparison with the cardiovascular pharmacophores depression models gave r values of 0.551 (P<0.05) and 0.407 (ns) for Cl(s) (for electrostatic and steric models) and -0.225 and -0.448 for Vd(ss) (both ns).

CONCLUSIONS

Comparison of CoMFA models for drug disposition show only small elements of commonality, suggesting different molecular features may be responsible are two properties. There was better similarity for both disposition pharmacophores with the pharmacophores for cardiovascular depression.