Experiment 3: Ointment

Title

Evaluation on the effect of different composition of emulsifying wax on the characteristics of

a suspension.

Objectives

1. To investigate the effects of different composition ointment on the physical characteristics of the prepared ointment.
2. To determine rate of drug diffusion from the ointment.

Introduction

Ointments are used topically for several purposes, e.g., as protectants, antiseptics, emollients and others. 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 neither penetrates the human skin barriers nor facilitates the absorption of substances through this barrier. 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, be non-greasy and effectively penetrate the skin.

Apparatus

Weighing machine, Weighing boat, 250ml beaker, Heater, Glass slab and spatula, Mortar and pestle, Dialysis beg (10cm), Thread, Glass rod, Water bath, Pipet bulb(5ml), Plastic cuvette, Spectrophotometer UV

Materials

Emulsifying Wax, White soft paraffin, Liquid paraffin, Acetylsalicylic acid, Distilled water

Procedures

1. 50g ointment was prepared using following formula:

Emulsifying ointment	Ingredients			Total
	Emulsifying wax	White soft paraffin	Liquid paraffin
	21	25	4	50
	17	25	8	50
	13	25	12	50
	9	25	16	50

2. 5g ointment was taken and put on a weighing boat and labelled. Texture, clarity, and colour of ointment was differentiated and explained.
3. 30g ointment was levigated with 1.5g acetylsalicylic acid glass slab. The powder was grinded in mortar and pestle.
4. Acetylsalicylic acid ointment was put into dialysis beg with the both ends was tied with two piece of thread.
5. The beg was then put in a beaker containing 100ml of distilled water which previously was heated until 37◦C.
6. For every five minutes 3-4ml of sample was pipette into plastic cuvette and examine using spectrophotometer UV. Make sure distilled water was stirred before taking the sample.

Results and Discussions:

1) Compare and discuss physical characteristics of ointment formed.

 

Group	Group 1	Group 2	Group 3	Group 4
1.Texture a.Spreadibility	Poorly spread	Not easily spread	Easily Spread	Easily spread
b.Greasiness	Less greasy	Slightly Greasy	Less Greasy	Greasy
c.Hardness	Hardest	Harder	Less Hardness	Less hard
2.Transparency	Clearer	Slight Transparent	Turbid	Turbid
3.Colour	White	White	White	White

As the amount of emulsifying wax is decreasing and the amount liquid paraffin is increasing from formulation 1 to 4, the ointment becomes softer, smoother, greasier and have better spreadibility. Ointments 4 from groups 1 and 4 are smoothest, opaque and white in colour due to the presence of highest amount of liquid paraffin. Ointments 1 are the stiffest and appears clearer compared to the other three ointments because it has the highest amount of emulsifying wax and the lowest amount of liquid paraffin. Higher concentration of emulsifying wax and lower concentration of liquid paraffin produce harder ointment.

2) Graph of UV absorption against time for ointment. Explain.

Based on the graph, the UV absorption from the water sample increased steadily over time. Therefore, on the graph, a linear line is obtained. The ointment is made with 21g of emulsifying wax, 25g white soft paraffin, 4g liquid paraffin and 1.5g of acetylsalicylic acid. Since the ointment was made with higher amount of emulsifying wax than the liquid paraffin, the ointment came out harder and has high viscosity (in liquid form during heating)  based on the physical appearance.

            Depending on partition coefficient, for drug that is very soluble in the vehicle, the tendency for the drug to leave the vehicle is small hence the rate of drug releasing will be slow. Acetylsalicylic acid is a weakly acidic drug and slightly soluble in water. The bases that aids in the releasing of the hydrophilic drugs are bases that are made from fatty bases or hydrocarbon bases. Emulsifying wax, liquid paraffin and white soft paraffin are hydrocarbon bases. Therefore, they provide good rate of drug releasing from the ointment.

            Since acetylsalicylic acid is a polar drug, it diffuses easily from the plastic bag towards the water in the beaker. The steady rate of releasing drug from the ointment and also combined with the easy diffusion of the drug across the plastic bag, causes a constant increasing of UV absorption over time that is shown in the graph (linear graph).

3) Result for emulsifying ointment I, II, III and IV

Time (min)		Emulsifying Ointment
		I	II	III	IV
Average UV absorption at 300nm (x ± SD)	0	0.2500±0.2500	0.2455±0.2175	0.0930±0.0630	0.0185±0.0065
	5	0.2650±0.2970	0.2830±0.2120	0.0225±0.0015	0.0410±0.0280
	10	0.2780±0.2600	0.2915±0.1905	0.0375±0.0095	0.4065±0.3935
	15	0.2875±0.2585	0.3305±0.1635	0.0415±0.0195	0.0650±0.0380
	20	0.2975±0.2575	0.3375±0.1465	0.0600±0.0235	0.0950±0.0580
	25	0.3065±0.2575	0.3780±0.1270	0.0480±0.0190	0.0980±0.0650
	30	0.3130±0.2590	0.3830±0.1430	0.0690±0.0530	0.1285±0.0595
	35	0.3255±0.2575	0.4115±0.1015	0.0575±0.0415	0.1700±0.1020
	40	0.4375±0.2625	0.4305±0.0875	0.0780±0.0520	0.1935±0.0845
	45	0.3550±0.2570	0.4130±0.1600	0.081±0.0580	0.2385±0.0955
	50	0.3755±0. 0.2665	0.3885±0.1325	0.0645±0.0375	0.2310±0.0950
	55	0.3895±0.2615	0.4210±0.1340	0.0645±0.0665	0.2895±0.1120
	60	0.3960±0.256	0.4445±0.0975	0.0595±0.0105	0.3560±0.1330

            The graph shows the UV average absorption of the ointments with different amount of emulsifying wax and liquid paraffin against the time in minutes. The UV absorption indicates the release of Acetylsalicylic acid from the ointment. If the UV absorption increases, it means the release of the drug from the dialysis bag into the distilled water is high. From the graph, emulsifying ointment I gives lowest UV absorption value and almost constant, while the value of the UV absorption for emulsifying ointment IV is the highest, which increases with time.

            Ointment I contains the highest amount of emulsifying wax, which is 21g. It can affect the release of the drug from the ointment. High amount of emulsifying wax cause the ointment to become harder, thus gives difficulty for the drug to be released out into the distilled water. The amount of emulsifying wax in the ointment IV is the lowest, which is 9g. Since the presence emulsifying wax is very little, the drug can diffuse out of the ointment easily. Plus, Acetylsalicylic acid is a hydrophilic drug. It will diffuses out and dissolves with the presence of water.

There may be errors occurred during the experiment that cause the result not so accurate. For example, the solution sample taken for the UV absorption test is not stirred before it is taken. The time for the sample taken is not accurate also. The insertion of the ointment into the dialysis bag is not done well. This may cause

4)  The function of the materials in the ointment. How does the different emulsifying wax and liquid paraffin components affect the physical appearance of the ointment formed and the release rate of the drug from the ointment?

            Emulsifying wax is an emulsifying agent that is used to stabilise the oil droplets in ointment. This is to ensure the oil droplets will soluble and mix with the water for the formation of the ointment. If without the emulsifying wax, the oil droplets will merge together and phase separation occur where the ointment cannot be formed. It also allows the ointment to have self-emulsifying property. Liquid paraffin and soft paraffin are the hydrophobic bases of the ointment. Liquid paraffin softens the ointment formed and reduces the viscosity of the ointment in the presence of emulsifying wax. It increases the spreadibility and decreases the hardness of the ointment. White soft paraffin enhances the penetration of acetylsalicylic acid through skin surface as well as the absorption through the membrane into circulation.

             From the experiment, different proportions of materials are used to produce 50g of emulsifying ointment. High concentration of emulsifying wax will make the ointment harder while a high concentration of liquid paraffin produces a watery, greasy, and soft ointment due to the reduced viscosity of ointment. Therefore, higher concentration of emulsifying wax and lower concentration of liquid paraffin produce harder and less greasy ointment compared to lower concentration of emulsifying wax and higher concentration of liquid paraffin in an ointment formulation.

In this formulation, the increased concentration of emulsifying wax reduces the rate of drug released from ointment. This is because higher amount of emulsifying wax will decrease the drug diffusion from ointment by holding the active ingredient (acetylsalicylic acid) tightly and thus slow down the drug released. On the other hand, diffusion rate of acetylsalicylic acid from the dialysis tube is increased in a formulation of ointment with optimum concentration of liquid paraffin because acetylsalicylic acid which is hydrophilic is tend to diffuse into the surrounding distilled water. Hence, the release rate of drug is increased. However, the diffusion rate of acetylsalicylic acid will decrease when the concentration of liquid paraffin is beyond the optimum value. Thus, an optimum ratio of the phases is needed to produce an ointment with good physical property and also the drug releasing rate.

Conclusion

The physical characteristic of the ointment will be different when the ointment composition is different.

The ointment with less liquid paraffin and more emulsifying wax will produce a harder ointment which also has a low rate of drug release. As the amount of emulsifying wax is decreasing and the amount liquid paraffin is increasing, the ointment becomes softer, smoother, greasier and have better spreadibility.

Correct proportion of emulsifying wax will ensure the hydrophobic and hydrophilic phase to be uniformly distributed between each other.

The rate of drug release will be reduced by the high amount of emulsifying wax

Higher amount of emulsifying wax will decrease the drug diffusion from ointment by holding the active ingredient tightly and thus retard the drug release.

Reference

1. Aulton, M.E.2002. Pharmaceutics: The Science of Dosage Form Design. Edinburgh: Churchill Livingstone.

2. Eccleston, G.M. 1997. Colloids and Surfaces A: Physicochemical and Engineering Aspects. Functions of mixed emulsifiers and emulsifying waxes in dermatological lotions and creams 123–124: 169–182

3. http://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/4290121/SUPPOSITORIES.pdf

4. http://www.ausetute.com.au/aspirin.html