Changes in Propofol Concentration in a Propofol-Lidocaine 9:1 Volume Mixture

A New Anaesthetic Protocol for Adult Zebrafish (Danio rerio): Propofol Combined with Lidocaine

Background

The increasing use of zebrafish model has not been accompanied by the evolution of proper anaesthesia for this species in research. The most used anaesthetic in fishes, MS222, may induce aversion, reduction of heart rate, and consequently high mortality, especially during long exposures. Therefore, we aim to explore new anaesthetic protocols to be used in zebrafish by studying the quality of anaesthesia and recovery induced by different concentrations of propofol alone and in combination with different concentrations of lidocaine.

Material and Methods

In experiment A, eighty-three AB zebrafish were randomly assigned to 7 different groups: control, 2.5 (2.5P), 5 (5P) or 7.5 μg/ml (7.5P) of propofol; and 2.5 μg/ml of propofol combined with 50, (P/50L), 100 (P/100L) or 150 μg/ml (P/150L) of lidocaine. Zebrafish were placed in an anaesthetic water bath and time to lose the equilibrium, reflex to touch, reflex to a tail pinch, and respiratory rate were measured. Time to gain equilibrium was also assessed in a clean tank. Five and 24 hours after anaesthesia recovery, zebrafish were evaluated concerning activity and reactivity. Afterwards, in a second phase of experiments (experiment B), the best protocol of the experiment A was compared with a new group of 8 fishes treated with 100 mg/L of MS222 (100M).

Results

In experiment A, only different concentrations of propofol/lidocaine combination induced full anaesthesia in all animals. Thus only these groups were compared with a standard dose of MS222 in experiment B. Propofol/lidocaine induced a quicker loss of equilibrium, and loss of response to light and painful stimuli compared with MS222. However zebrafish treated with MS222 recovered quickly than the ones treated with propofol/lidocaine.

Conclusion

In conclusion, propofol/lidocaine combination and MS222 have advantages in different situations. MS222 is ideal for minor procedures when a quick recovery is important, while propofol/lidocaine is best to induce a quick and complete anaesthesia.

In vitro and in vivo evaluation of a simple microemulsion formulation for propofol

The aim of the present study was to develop an oil-free o/w microemulsion, composed of pluronic F68, propylene glycol and saline, which solubilized poorly soluble anesthetic drug propofol for intravenous administration. The ternary diagram was constructed to identify the regions of microemulsions, and the optimal composition of microemulsion was determined by in vitro evaluation such as globule size upon dilution and rheology. The droplet size of the diluent emulsion corresponding to oil-in-water type ranged from 200 to 300nm in diameter. Stability analysis of the microemulsions indicated that they were stable upon storage for at least 6 months. Hemolysis percent of propofol microemulsions was lower than that of commercial lipid emulsion (CLE) at 4h. Acute toxicity test showed that median lethal dose of propofol microemulsion was the same as that of CLE. No significant difference in time for unconsciousness and recovery of righting reflex was observed between the prepared microemulsions and CLE. In conclusion, microemulsion would be a promising intravenous delivery system for propofol.

Reduction of pain on injection of propofol: combination of pretreatment of remifentanil and premixture of lidocaine with propofol

BACKGROUNDS AND OBJECTIVE

There is a high incidence of pain following intravenous injection of propofol, and many studies have been conducted to find a way of reducing this. The administration of lidocaine and, recently, remifentanil has also been used for this purpose, but it is only partially effective. Thus, the purpose of this study was to investigate the analgesic effect of a combination of pretreatment with remifentanil and premixture of lidocaine with propofol and to compare either treatment alone during propofol injection in dorsal hand-veins.

METHODS

In a prospective, randomized, double-blinded trial, we studied 141 adult patients scheduled for elective surgery. The combination of pretreatment of remifentanil (0.35 microg kg(-1) min(-1)) and a premixture of lidocaine with propofol (mixture of propofol 1% and lidocaine 1% in a 10:1 ratio) was compared with either treatment alone in the prevention of pain on propofol injection. Pain was assessed on a four-point scale (0=none, 1=mild, 2=moderate, 3=severe) during propofol injection. Patients in Group B received remifentanil (0.35 microg kg(-1) min(-1)) 30 s before the injection of propofol.

RESULTS

The reduction of pain on propofol injection was similar in both the remifentanil pretreatment and lidocaine premixture groups (62.2% vs. 62.2%). Combination therapy was associated with a higher incidence of patients without pain (91.3%) than either treatment alone (P<0.001). On analysing the injection pain scores, we found a significant reduction of the score in the remifentanil and lidocaine Group C compared with the lidocaine Group A (P<0.001) and the remifentanil Group B (P<0.001).

CONCLUSIONS

The combination of pretreatment of remifentanil and premixture of lidocaine with propofol was more effective in reducing the incidence of pain on injection of propofol than either treatment alone.

Development of propofol-loaded microemulsion systems for parenteral delivery

The aim of the present study was to develop the aqueous parenteral formulation containing propofol using o/w microemulsion systems. Propofol itself was chosen as the oil phase and its content was fixed to 1%, w/w. Pseudoternary phase diagrams were constructed to obtain the concentration range of surfactant and cosurfacatnt and the optimum ratio between them for microemulsion formation. Consequently, the suitability of the chosen microemulsion system as a parenteral formulation was evaluated from the stability and hemolysis tests on that. Among the surfactants and cosurfactants screened, the mixture of Solutol HS 15-ethyl alcohol (5/1) showed the largest o/w mocroemulsion region in the phase diagram. When 1% (w/w) of propofol was solubilized with 8% (w/w) of Solutol HS 15-ethyl alcohol (5/1), the average droplet size (150 nm) and the content of propofol in the systems were not significantly changed at 40 degrees C for 8 weeks. The hemolysis test showed that this formulation was nontoxic to red blood cells. In conclusion, propofol was successfully solubilized with the o/w microemulsion systems.