Optimization, and in vitro and in vivo evaluation of etomidate intravenous lipid emulsion

Abstract

The aim of this investigation was to develop an etomidate intravenous lipid emulsion (ETM-ILE) and evaluate its properties in vitro and in vivo. Etomidate (ETM) is a hydrophobic drug, and organic solvents must be added to an etomidate injectable solution (ETM-SOL) to aid dissolution, that causes various adverse reactions on injection. Lipid emulsions are a novel drug formulation that can improve drug loading and reduce adverse reactions. ETM-ILE was prepared using high-pressure homogenization. Univariate experiments were performed to select key conditions and variables. The proportion of oil, egg lecithin, and poloxamer 188 (F68) served as variables for the optimization of the ETM-ILE formulation by central composite design response surface methodology. The optimized formulation had the following characteristics: particle size, 168.0 ± 0.3 nm; polydispersity index, 0.108 ± 0.028; zeta potential, -36.4 ± 0.2 mV; drug loading, 2.00 ± 0.01 mg/mL; encapsulation efficiency, 97.65% ± 0.16%; osmotic pressure, 292 ± 2 mOsmol/kg and pH value, 7.63 ± 0.07. Transmission electron microscopy images showed that the particles were spherical or spheroidal, with a diameter of approximately 200 nm. The stability study suggested that ETM-ILE could store at 4 ± 2 °C or 25 ± 2 °C for 12 months. Safety tests showed that ETM-ILE did not cause hemolysis or serious vascular irritation. The results of the pharmacokinetic study found that ETM-ILE was bioequivalent to ETM-SOL. However, a higher concentration of ETM was attained in the liver, spleen, and lungs after administration of ETM-ILE than after administration of ETM-SOL. This study found that ETM-ILE had great potential for clinical applications.

Keywords: Etomidate; intravenous lipid emulsion; pharmacokinetics; response surface methodology; tissue distribution.

Figure 1.

Structure of ETM.

Figure 2.

Solubility of ETM in PBS (A) and different oils (B) (n = 3).

Figure 3.

Effect of pressure and the number of cycles in high pressure homogenization on particle size and PDI (A: 700 bar; B: 1000 bar; C: 1300 bar) (n = 3).

Figure 4.

Properties of ETM-ILE prepared using different oil phases (n = 3).

Figure 5.

The CCD-RSM of three factors on the droplet size in ETM-ILE. (A: soybean oil and F68; B: egg lecithin and F68; C: egg lecithin and soybean oil).

Figure 6.

Characterization of ETM-ILE. (A) size detected by Zetasizer; (B) ZP detected by Zetasizer; (C) TEM image (scale bar 200 nm); (D) TEM image (scale bar 100 nm).

Figure 7.

Safety tests for ETM-ILE: (A) In vitro hemolysis test for ETM-ILE, tubes 1–5 were experimental group, tube 6 was the negative control, and tube 7 was the positive control; Images of the pathological sections of rabbit ear at the site of administration (HE staining, 200× magnification) of the three groups: ETM-SOL group (B), ETM-ILE group (C), and Normal saline group (D).

Figure 8.

Mean plasma concentration-time profile of ETM after administration of ETM-ILE and ETM-SOL at a dose of 5.0 mg/kg (n = 6).

Figure 9.

Tissue distribution of ETM after administration of ETM-ILE and ETM-SOL at doses of 5.0 mg/kg (n = 6).