Method-
The purpose of this laboration was a) to learn how to make an oil/water (o/w) emulsion and b) to investigate the release of local anaesthetics from an (o/w) emulsion cream composed of an 1:1 eutectic mixture of lidocaine/prilocaine determined by Photon Correlation Spectroscopy (PCS) (which determines the particle size) and by an in vitro experiment together with an UV/VIS detector
Step 1 Preparation of emulsion cream
As instructed by the laboratory manual, the following substances were weighed: Lidocaine (1,0025 g), prilocaine (1,0152 g) and surfactant Croduret 54-SO (0,7638 g) was weighed. All the components were melted under gentle heating (~50C) with a with a magnetic stirrer. Thereafter, water (7,2 ml) was added and the mixture was stirred (protected with parafilm) for 15 min without heat. The emulsion was ultra sonicated with 10 pulses. Secondly, water (27,0ml) was added to a 100ml beaker followed by a polymer Carbopol 934 (0,4035 g) used as thickening agent. The mixture was protected with parafilm and left under stirring until all macroscopic particles were dissolved (35 min). 1,2 ml of 5M NaOH was added under frequent stirring. The solution then turned thick and pH was measured to 13.
In the next step 4,0784 g of the emulsion concentrate was mixed with 12,0506 g of the thickener to assemble the cream. The cream obtained was like jelly and had a clear colour.
Step 2 Particle size measurements
1,5 ml of the sonicated emulsion from step 1 was transferred to a cuvette for particle size measurement in a PCS (with instalments: 25C, equilibration time: 2 min). The sample was diluted about 20 times before it was run in the PCS to measure the droplet size. The PSC technique is based on the Brownian motion of the particles (which is the random motion that particles have) thus causing different intensity of light scattering when an applied light source (laser) hits the particles.
The intensity of the light scattering depend on the particle size. The light scattering is then processed with certain equations one being the Stokes-Einstein Equation resulting in the hydrodynamic diameter or the particles. Generally, the smaller the particle, the longer time to detect and conversely.
Step 3 In vitro experiment
1,806 g of the cream was put in a cell, which then was enclosed with a membrane. The cell was put in a water bath and the absorption at 222,2 nm was measured over two hours by taking a small sample that was run in an UV/VIS spectroscopy at regular times (the sample was put back in the water bath after every measurement to keep constant volume).
In vitro experiment
Following is a table consisting the different times at when the measurements were taken (t0) and the absorbance (abs) the UV/VIS spectroscopy gave:
|
Time
|
Abs
|
|
t0
|
0,107
|
|
5
|
0,222
|
|
10
|
0,29
|
|
15
|
0,345
|
|
20
|
0,403
|
|
25
|
0,439
|
|
30
|
0,48
|
|
35
|
0,525
|
|
40
|
0,56
|
|
45
|
0,603
|
|
60
|
0,655
|
|
75
|
0,741
|
|
90
|
0,818
|
|
105
|
0,89
|
|
120
|
0,968
|
To make the values of the absorbance more accurate initial in the experiment a blank was measured at t0 giving 0,107. The table below show all the measurements, but with the blank taken into account (subtracted from the measured values for the abs).
|
Time
|
Abs-blank
|
|
5
|
0,115
|
|
10
|
0,183
|
|
15
|
0,238
|
|
20
|
0,296
|
|
25
|
0,332
|
|
30
|
0,373
|
|
35
|
0,418
|
|
40
|
0,453
|
|
45
|
0,496
|
|
60
|
0,548
|
|
75
|
0,634
|
|
90
|
0,711
|
|
105
|
0,783
|
|
120
|
0,861
|
Report
Written report where method, results, and discussion and also answers to the questions below are included. To some questions you need two articles from Journal of Pharmaceutical sciences which you have been handed.
1) Describe shortly the mechanism for drug release from your cream. What is the function of the emulsion droplets?
2) It is possible from the mechanism to identify two potential rate determining steps. Which are these?
3) What is the advantage of using a 1:1 mixture of lidocaine and prilocaine as oilphase instead of pure lidocaine or prilocaine?
4) Make a graph that shows released number of moles lidocaine + prilocaine as function of time.
5) How big fraction of the total mass of (L+P) used in the cell has been released? Assume that L and P have been released in the same amounts.
6) In the first (steepest) part of the graph in 3), fit a line by linear regression and calculate the flow of lidocaine + prilocaine per membrane surface unit and unit time. Membrane surface: ~20.4cm2 or smaller if you had air bubbles. Compare with table 3, April 1986. Recall that your cream had a concentration of 5 weight-% L+P.
7) Discuss the graph in figure 4, November 1985 for the three different phases of lidocaine and prilocaine. Note that it is the fraction of L+P in a certain phase that is plotted on the yaxis, not the total amount or concentration.
8) Discuss the graph in figure 4, April 1986. How does an increase in L+P concentration and surfactant concentration affect the drug release? Why?
9) Describe briefly how a PCS instrument works and what limitations it has. Also compare your results with the particle sizes given in table 1, Nov 1985. Do they seem to have a wider or thinner distribution than you have?
Attachment:- Assignment.rar