OBJECTIVE:
To study
the influence of ointment composition towards the physical properties of the
ointment and the rate of drug release from the ointment formulation.
INTRODUCTION:
Ointment is a highly viscous or semisolid substance used on the skin as a cosmetic, emollient, or medicament; a salve. It is a semisolid medicinal preparation usually having a base of fatty or greasy material. Ointments are used topically for several purposes, e.g. as protectants, antiseptics, emollients, antipruritics, kerotolytics, and astringents. The vehicle or base of an ointment is of prime importance if the finished product is expected to function as any one of the above categories.
In the case of a protective ointment, it serves to protect the skin against moisture, air, sun rays and other external factors. It is necessary that the ointment either penetrates the human skin barriers or facilitates the absorption of substances through this barrier. An antiseptic ointment is used to destroy or inhibit the growth of bacteria. Frequently bacterial infections are deeply seated; a base which has the capacity to either penetrate or dissolve and release the medication effectively is therefore desired. Ointments used for their emollient effect should be easy to apply, non-greasy and effectively penetrate the skin. This type of ointment increases the moisture of skin. There are five classes or types of ointment bases which can be differentiated on the basis of their physical composition. They are oleaginous bases, absorption bases, water in oil emulsion bases, oil in water emulsion bases and water soluble or water miscible bases. Each ointment base type has different physical characteristics and therapeutic uses based upon the nature of its components.
APPARATUS:
Weighing
balance
|
2
threads
|
Weighing
boat
|
1
glass rod
|
100ml
beaker
|
Water-bath
|
Heater
|
1 set
of pipette (5 ml) and pipette –bulb
|
1 set
of slap and spatula
|
1
plastic cuvette
|
1 set
of mortar and pestle
|
Spectrophotometer
UV/Vis
|
1
dialysis beg (10cm)
|
MATERIALS:
Emulsifying
Wax
White
soft paraffin
Liquid
Paraffin
Acetylsalicylic
acid
Distilled-water
PROCEDURES:
1.
Emulsifying ointment (50 g) with the formula below was prepared:
2.
Little ointment (5g) which was formed was taken and placed into the weighing
boat and was labelled. Texture (spreadability, greasiness and hardness),
clarity, and colour of the formed ointment were analyzed and compared.
3. Acetylsalicylic
acid powder (1.5g) was incorporated into the 30 g ointment formed with the levigation
technique (Acetylsalicylic acid powder was triturated with the pestle and
mortar).
4.
Acetylsalicylic acid ointment was inserted into the dialysis bag and two ends
of the bed were tied properly as shown in the figure below:
5. The
bed was placed into the beaker (250 ml) which contain distilled water (100 ml)
which had been heated to 37°C.
6. A
aliquot sample (3-4 ml) was pipetted at the interval 5 minutes and the release
of the Acetylsalicylic acid from the ointment base was determined by the
spectrophotometer UV-visible. The distilled water was stirred with the glass
rod before sampling.
RESULTS AND DISCUSSIONS:
1. Compare
the physical properties of the ointments formed and give your comments on them.
Ointment
Physical appearence
|
I
|
II
|
III
|
IV
|
|
1. Texture
a) Spreadibility
b) Greasiness
c) Hardness
|
Very difficult
A bit greasy
Very hard
|
Difficult
Less greasy
Hard
|
Greasy
Soft
|
Very easy
Very greasy
Very soft
|
|
2. Turbidity
|
Very turbid
|
Turbid
|
Less turbid
|
Less turbid
|
|
3. Colour
|
White
|
White
|
White
|
White
|
|
In this experiment, the difference of the ointments made by different groups was the amount of emulsifying wax and liquid paraffin used. Meanwhile, the amount of white soft paraffin used was the same for every group.
Based on the observation on the ointments formed from every group, comparison is made on the aspects of texture, clarity and the colour of the ointments. For the texture, spreadibility, greasiness and hardness are taken into account for comparison. The spreadability and hardness of ointment is dependent on the amount of emulsifying wax used. Ointment I had the highest amount of emulsifying wax (21g), thus the ointment was the most difficult to spread and the hardest among the 4 ointments. Meanwhile, ointment IV was the softest and easiest to spread due to the least amount of emulsifying wax used (9g). In addition, ointment III was easier to spread and softer compared to ointment II as it contained less emulsifying wax. Apart from the contribution of emulsifying wax, liquid paraffin also will affect the hardness of ointment. The lower the content of liquid paraffin used, the harder the ointment formed.
Besides, the presence of liquid paraffin determines the greasiness of the ointment. The highest content of liquid paraffin (16g) in emulsifying ointment IV make it the greasiest ointment compared to ointments I, II and III. Ointment I was the least greasy due to the lowest amount of liquid paraffin used (4g).
For the comparison of turbidity, the physical appearance of emulsifying ointment I was the most turbid and the turbidity become less and less proceeding to the ointment IV due to the amount of liquid paraffin used. The higher the content of liquid paraffin used in the ointment, the lesser the degree of turbidity of ointment.
For the appearance or colour of the ointment, all of the ointments formed were white in colour because liquid paraffin which is white gave its colour to the ointments.
2. Plot the graph of UV absorption against
time. Give explanation.
Time(min)
|
UV Absorption at 310 nm
|
0
|
0.000
|
5
|
0.104
|
10
|
0.168
|
15
|
0.183
|
20
|
0.219
|
25
|
0.278
|
30
|
0.321
|
35
|
0.237
|
40
|
0.278
|
45
|
0.300
|
50
|
0.362
|
55
|
0.383
|
60
|
0.428
|
In this experiment, the dialysis bag resembled the human skin where the absorption of drug occurs when the drug crosses the membrane into the layers of the skin. The concentration of the drug in the distilled water represents the amount of drug absorbed into the blood circulation and also the bioavailability of the drug.
UV absorption is equal to the amount of drug that has crossed the membrane. The experiment showed that generally the UV absorption is proportional to the time throughout the experiment duration. By theory, UV absorption is proportional to the release time of acetylsalicylic acid from the tube. The gradient of the graph shows the rate of release of acetylsalicylic acid from the membrane.
The graph shows that in the beginning, the concentration of the acetylsalicylic acid in the distilled water increased with time. As the time increased until a particular time, the releasing rate reduced (gradient of the graph decreased). This condition can be explained as the graph achieved its saturation point. At the late stage of experiment, the releasing rate increased sharply. This maybe due to experimental errors such as the tube may not be tied tightly enough or maybe the presence of leakage on the membrane and therefore could not withstand the stirring.
At the beginning of the experiment, the distilled water was kept at 37°C and it was hypotonic to the tube content, which consisted of acetylsalicylic acid. Thus, acetylsalicylic acid tended to diffuse out from the tube to the hypotonic solution (distilled water).
As the time increased, the concentration of salicylic acid in the distilled water increased. As the experiment proceeded, the concentration of the acetylsalicylic acid in the tube became isotonic with the distilled water in the surrounding. This showed that the equilibrium for diffusion of acetylsalicylic acid into and out of the tube was achieved. At this time, the gradient of the graph reduced.
There might be some errors that happened and caused the inaccuracy of the results. The concentration of acetylsalicylic acid may not be consistent if the distilled water in the beaker was not stirred uniformly. Besides, it was important to keep the constant temperature of the water bath. In addition to that, the technique of using spectrophotometry device also played a vital role in getting accurate results. The smooth surface of the cuvette should face the source of UV light and the smooth surface should be cleaned before it was placed into the device. When we were holding the cuvette, it was not advisable to hold the smooth surface (where there is a triangle symbol on it).
3. Plot a graph of UV absorption versus time for
ointments that have different compositions. Compare and discuss the results.
Time (min)
|
UV Absorption of at 300
nm
|
||||||||||||||
0
|
5
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
50
|
55
|
60
|
|||
Emulsifying
Ointment
|
I
|
1
|
0
|
0.423
|
0.44
|
0.464
|
0.521
|
0.579
|
0.586
|
0.591
|
0.636
|
0.638
|
0.655
|
0.730
|
0.738
|
5
|
0
|
0.098
|
0.105
|
0.120
|
0.127
|
0.153
|
0.175
|
0.183
|
0.192
|
0.214
|
0.255
|
0.271
|
0.296
|
||
II
|
2
|
0
|
0.104
|
0.168
|
0.183
|
0.219
|
0.278
|
0.321
|
0.237
|
0.278
|
0.300
|
0.362
|
0.383
|
0.428
|
|
6
|
0
|
0.145
|
0.186
|
0.193
|
0.226
|
0.305
|
0.318
|
0.338
|
0.352
|
0.353
|
0.407
|
0.412
|
0.435
|
||
III
|
3
|
0
|
0.052
|
0.049
|
0.146
|
0.100
|
0.183
|
0.220
|
0.286
|
0.253
|
0.277
|
0.274
|
0.319
|
0.387
|
|
7
|
0.052
|
0.114
|
0.122
|
0.141
|
0.150
|
0.154
|
0.200
|
0.220
|
0.274
|
0.293
|
0.341
|
0.360
|
0.417
|
||
IV
|
4
|
0
|
0.051
|
0.164
|
0.086
|
0.140
|
0.175
|
0.225
|
0.183
|
0.228
|
0.200
|
0.215
|
0.206
|
0.230
|
|
8
|
0
|
0.036
|
0.040
|
0.065
|
0.082
|
0.109
|
0.122
|
0.141
|
0.177
|
0.180
|
0.225
|
0.246
|
0.25
|
||
Time (min)
|
Average UV Absorption at 300 nm (Mean ± SD)
| |||||||||||||
0
|
5
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
50
|
55
|
60
| ||
Emulsifying Ointment
|
I
|
0
|
0.2605±
0.1625
|
0.2740±
0.1690
|
0.2920±
0.1720
|
0.3240±
0.1970
|
0.3660±
0.2130
|
0.3805±
0.2055
|
0.3870±
0.2040
|
0.4140±
0.2220
|
0.4260±
0.2120
|
0.4550±
0.2000
|
0.5005±
0.2295
|
0.5170±
0.2210
|
II
|
0
|
0.1245±
0.0205
|
0.1770±
0.0090
|
0.1880±
0.0050
|
0.2225±
0.0035
|
0.2915±
0.0135
|
0.3195±
0.0015
|
0.2875±
0.0505
|
0.3150±
0.0370
|
0.3265±
0.0265
|
0.3845±
0.0225
|
0.3975±
0.0145
|
0.4315±
0.0035
| |
III
|
0.0260±
0.0260
|
0.0830±
0.0310
|
0.0855±
0.0365
|
0.1435±
0.0025
|
0.1250±
0.0250
|
0.1685±
0.0145
|
0.2100±
|
0.2530±
0.0330
|
0.2635±
0.0105
|
0.2850±
0.0080
|
0.3075±
0.0335
|
0.3395±
0.0205
|
0.4020±
0.0150
| |
IV
|
0
|
0.0435±
0.0075
|
0.1020±
0.0620
|
0.0755±
0.0105
|
0.1110±
0.0290
|
0.1420±
0.0330
|
0.1735±
0.0515
|
0.1620±
0.0210
|
0.2025±
0.0255
|
0.1900±
0.0100
|
0.2200±
0.0050
|
0.2260±
0.0200
|
0.2400±
0.0100
| |
From the graph, ointment IV shows the smallest
gradient among the 4 slopes. This result is inaccurate as the result that we
expect is ointment IV should have the highest reading of released
acetylsalicylic acid. This is due to the presence of low emulfsying wax that
causes the matrix not fine enough to trap liquid paraffin and soft paraffin.
Incomplete matrix causes the emulsifying ointment formed to be unstable and
hence it cannot disperse evenly. As a result, this leads to the hydrophilic
ointment to diffuse into the distilled water through the membrane.
Meanwhile,
from the graph drawn above, we can know that ointment I shows the highest
release rate of acetylsalicyclic acid. The result is inaccurate because
ointment I is made up of formulation which contains high amount of emulsifying
wax and low quantity of liquid paraffin. This formulation is much more harder
than the other formulations. The matrix formed is very solid and has less
liquid. Hydrophilic aspirin may be able to disperse evenly in the ointment that
is emulsified by the emulsifying agents (emulsifying wax) and the oil phase
(liquid paraffin and soft paraffin) is not enough for the aspirin to diffuse
through the membrane. Thus the concentration of aspirin in the distilled water
is low. The uneven ratio causes it to be trapped in the ointment with the slow
release rate.
The inaccuracy of the result of our experiment may be due to the inconsistency of stirring of the distilled water before taking the aliquot sample out at interval of 5 minutes. The inconsistency of stirring may result in the uneven distribution of the acetylsalicylic acid. As such, when the aliquot sample is taken, there may be uneven amount of acetylsalicylic acid being taken for UV spectrophotometer determination. Other errors include the loss of ointment when transferring the ointment into the dialysis beg.
The inaccuracy of the result of our experiment may be due to the inconsistency of stirring of the distilled water before taking the aliquot sample out at interval of 5 minutes. The inconsistency of stirring may result in the uneven distribution of the acetylsalicylic acid. As such, when the aliquot sample is taken, there may be uneven amount of acetylsalicylic acid being taken for UV spectrophotometer determination. Other errors include the loss of ointment when transferring the ointment into the dialysis beg.
As such, several precautions should
be taken to reduce the errors made during the experiment. The distilled water
should be stirred continuously in order to ensure the uniform distribution of
acetylsalicylic acid. Besides, excess ointment should be made to overcome the
loss of ointment while transferring it into the dialysis beg.
4. What is the function of each ingredient used
in the preparation of the ointment? How does the use of different amounts of
emulsifying wax and liquid paraffin used influence the physical characteristic
of an ointment formulation and the rate of drug release from it?
The ingredients used in the
preparation of the ointment are emulsifying wax, liquid paraffin and white soft
paraffin. The emulsifying wax stiffens the ointment and give it its hardness. White
soft paraffin is a very greasy moisturiser. It works as a moisturiser by providing a layer of oil on the
surface of the skin to prevent water evaporating from the skin surface. It is
added into the ointment so that the ointment can soften, hydrate and protect
the skin and soothe any irritation, especially in patients with dry skin
conditions. Liquid paraffin also acts as an emollient which soothes, smoothes
and hydrates the skin. Liquid paraffin makes the ointment less viscous.
The higher the amount of emulsifying wax and the lower the amount of liquid paraffin used, the stiffer and the less greasy the ointment. The higher the amount of liquid paraffin also cause the ointment to be less viscous. Rate of drug release from the ointment decreases when the ointment contains a higher amount of emulsifying wax and a lower amount of liquid paraffin.
The higher the amount of emulsifying wax and the lower the amount of liquid paraffin used, the stiffer and the less greasy the ointment. The higher the amount of liquid paraffin also cause the ointment to be less viscous. Rate of drug release from the ointment decreases when the ointment contains a higher amount of emulsifying wax and a lower amount of liquid paraffin.
CONCLUSIONS:
Ointment composition can influence the physical properties of the
ointment and the rate of drug release from it. Ointment which contains a higher
amount of emulsifying wax and a lower amount of liquid paraffin is stiffer,
more viscous and less difficult to be spread. Therefore, the rate of drug
release also decrease with the increase in the amount of emulsifying wax and
the decrease in the amount of liquid paraffin used.
REFERENCES:
1. http://drugs.webmd.boots.com/drugs/drug-673-Cetraben.aspx
2.
http://drugs.webmd.boots.com/drugs/drug-491-WHITE+SOFT+PARAFFIN.aspx?drugid=491&drugname=WHITE%2BSOFT%2BPARAFFIN&source=2&isTicTac=false
3.
http://www.mathsisfun.com/data/standard-deviation-formulas.html
4. http://www.youtube.com/watch?v=b0rM5nxIUyQ
APPENDICES:
Emulsifying wax was melted first on the evaporating dish due to its higher melting point. When most of the emulsifying wax had melted, white soft paraffin was then added to the same evaporating dish. The evaporating dish was heated on the magnetic stirrer.
We removed the evaporating dish from the magnetic stirrer when the mixture was completely melted. Liquid paraffin was then added into the mixture.
Following liquefication, the mixture was allowed to congeal. The mixture was stirred until it began to congeal. An ointment was then formed.
The ointment was incorporated with acetylsalicylic acid powder and was levigated on a glass slab.
5g of the acetylsalicylic acid ointment was taken out and put into a weighing boat to observe the texture of the ointment formed.
The ointment formed was inserted into the dialysis bag. It was quite tough as the opening of the dialysis bag was very small.
4mL of the sample was pipetted into a cuvette.
The cuvette containing the sample was then inserted into the UV spectrometer to determine the amount of acetylsalicylic acid released from the dialysis bag.
The reading shown on the UV and visible spectrometers measured the amount of ultraviolet and visible light transmitted or absorbed by the sample.
