EXPERIMENT 4 : SUPPOSITORY

TITLE :
TEST FOR THE EFFECT OF DIFFERENT CONCENTRATIONS OF INGREDIENTS ON THE CHARACTERISTICS OF THE SUPPOSITORY FORMULATION

Introduction:

     Suppositories are solid formulations consist of various weights and shapes, adapted for introduction into the rectal, vaginal, or urethral route of the human body. They usually melt, soften, or dissolve at body temperature. A suppository may act as a protectant to the local tissues located near the point of insertion or as a carrier of therapeutic agents for systemic or local action. Suppository bases usually employed are cocoa butter, glycerinated gelatin, hydrogenated vegetable oils, mixtures of polyethylene glycols of various molecular weights, and fatty acid esters of polyethylene glycol.

The suppository base used, can influence the release of the active ingredient incorporated in it. While cocoa butter melts quickly at body temperature, it is immiscible with body fluids and this inhibits the diffusion of fat-soluble drugs to the affected sites. Polyethylene glycol is a suitable base for some antiseptics. In cases where systemic action is expected, it is preferable to incorporate the ionized form instead of the nonionized form of the drug, in order to maximize bioavailability. Although nonionized drugs partition more readily out of water-miscible bases such as glycerinated gelatin and polyethylene glycol, the bases themselves tend to dissolve very slowly and thus will slow down the release of the drug. Oleaginous vehicles such as cocoa butter are seldom used in vaginal preparations because of the nonabsorbable residue formed, while glycerinated gelatin is seldom used rectally because of its slow dissolution.

Materials and Methods :

A.   Apparatus

Electronic balance.                                      Water-bath at 37°C

Weighing boats.                                           Dialysis bag (10 cm)

50 mL beaker.                                             Two strings of thread

100 mL beaker.                                           Glass rod

Heating instrument (hotplate).                       5 mL pipette

5 mL measuring cylinder.                              Pipette filler

Suppository mould set.                                 Plastic cuvette

Spatula.                                                        UV Spectrophotometer

B.   Materials

Polyethylene glycol (PEG) 1000            Paracetamol

Polyethylene glycol (PEG) 6000

C.   Procedures

1.        Paracetamol Suppositories(10g) are prepared by using the formula provided:

2.        The shape of the suppositories are formed using suppository-mould provided. When the suppositories are formed, their shape, texture, and colour are observed.

3.        One suppository is placed into the 50mL beaker filled with distilled water (10 mL, 37°C in water bath) and time taken for the suppository to melt is recorded.

4.        One suppository is inserted into the dialysis bag and both ends of the bag are firmly tied. Then, the dialysis bag is placed into the 100mL beaker filled with distilled water (50 mL, 37°C in water bath).

5.        For every 5 minutes, one aliqout of sample(3-4 mL) is pipetted from the beaker and the release of Paracetamol from the suppository is determined by using UV-visible Spectrophotometer. The distilled water must be stirred with glass rod before the sample is taken.

Results:

Discussion:

1.        Compare the physical appearance of the suppositories and give explanation.

      Table: Characteristics of suppositories

The table above shows the comparison between the physical appearances of suppositories in those formulations based on the effects of different amount of the Polyethylene Glycol (PEG) in the suppository base mixtures. The two main bases are PEG 1000 and PEG 6000. Due to the latter contains more hydroxyl (-OH) bonds in its chemical structure, and thus present greater hydrophilicity compared to the previous one.

Meanwhile, hardness of the suppositories is more closely related to the chemical structure of the overall suppository. This could be explained, as the physicochemical characters of PEG 6000 forms more strong and stable hydrogen bonds in the suppository compared to PEG 1000. PEG 6000 is higher molecular weight compare to PEG 1000. Thus, it also has a lot of hydroxyl groups which can form numerous hydrogen bonds between the molecules of the PEG 6000 and the molecules of Paracetamol. Hence, we could see an increase in the hardness of the suppositories in line with the increasing amount of PEG 6000.

Greasiness and lustrous characteristics of the suppositories are both related to the amount and effect of PEG 1000, which is considered more hydrophobic than PEG 4000. As we can see, the amount of PEG 1000 decreases across the four formulations, and hence the greasiness and lustre characteristics decrease in the same degree. As the amount of PEG 1000 decreases with the increase of PEG 6000, the degree of greasiness decreases at the same time.

Suppository formed by higher amount of lower molecular weight polyethylene glycol is more transparent and is more lustrous in nature. This is shown by which Suppository I is most transparent and lustrous and then followed by suppository II, III and IV. Due to higher amount of PEG 6000 being used, suppositories formed will appear in white colour. This is indicated in Suppository II, III and IV. As the mould made for suppositories is bullet shaped, thus all four suppositories produced are bullet shaped.

2.      Plot a graph average time that is required to melt the suppository against different amount of PEG 6000 in formulation. Compare and discuss the results.

In this experiment, the formulation of suppository paracetamol containing two type of base which are polyethylene (PEG) 1000 and polyethylene (PEG) 6000.

Polyethylene glycols are available in average molecular weight ranging from 200 to 8000. This wide range of products provides flexibility in choosing properties to meet the requirements of many different applications. The physical and chemical stability of the formulation is not only affected due to different in molecular weight of PEG, but also the different amount of PEG with similar molecular weight used in the formulation can affect the physicochemical properties of the suppository.

The melting points of suppository is proportional to their molecular weights. Melting point increases as molecular weight increases. Besides that, melting point also may increase as the PEG in similar molecular weight but its content in the formulation is different. Increase amount of PEG used will increase melting point as well as time taken for formulation to melt.

Based on the result obtained, as the amount of PEG 6000 used in formulation is increased from 0g to 6g, the average time taken for suppository to melt is decreased. However, the average of time taken is increased gradually as the amount of PEG 6000 increased from 6g to 9g. The result obtained is not accurate as the theory. It is may be because there are some errors during formulated the suppository or conducted the experiment. Temperature of water bath must contant to ensure that suppository is melted on specific temperature. Besides that, the amount of PEG 6000 that incorporated in the formulation must measured accurately.

Standard deviation value on 9g 0f PEG 6000 is too small and this indicated that the value is close to the mean value. While standard deviation on 3g of PEG 6000 shows the larger value and this implies that the data points are farther from the mean value.

3. Plot a graph of UV absorption against time. Give reasons.

In this experiment, the drug was put inside the dialysis bag which immersed into the beaker containing distilled water maintained at 37ºC, which is same as our body temperature. This experiment was used to determine the absorption rate of the suppository when inserted into the rectum.  Dialysis bag represents human biological membrane while distilled water represents human blood plasma. All melting, drug release and drug absorption processes occur in water bath at 37ºC, which represents human body temperature. Firstly, the distilled water will enter into the dialysis bag due to its higher water concentration. The paracetamol suppository is melted at 37 ºC and also dissolved by water coming in and then flow out through the dialysis bag into distilled water.

The graph above shows the changes of UV absorption with the amount of Paracetamol released into distilled water with the increasing of time. In theory, we should get a sigmoid shape which indicates constant drug release rate until reaches equilibrium. But, the graph that we have obtained is different from theory which shows the unconstant  release of paracetamol. This may be due to some errors that occurred during the experiment. Firstly, it maybe due to uneven stirring of distilled water before it was taken to measure the reading. Besides, the distribution of paracetamol in our suppository is not homogenous. This may due to the air bubble trapped inside the suppository when the preparation is poured into the mould. So, these cause reduction in size and alter the drug release rate from suppository. On the other hand, the high frequency of removing the cover of hot plate makes the temperature of water does not maintain at 37ºC. Lastly, the reading was not taken at exactly 5 minutes interval.

4.      Plot graph of UV absorption against time for the suppository formulation with different compositions. Discuss and compare the results.

Graph of UV Absorption vs Time 

Y-axis=UV absorption value

X-axis=time (min)

Theoretically, the graph obtained should obey the sigmoid curve. But, the graph obtained by us does not obey the sigmoid curve. It shows that there is some fluctuation values. The results obtained shown on the graph are increased gradually and there is some drops. This shows the unusual sigmoid curve.       

            According to the experimental result obtained, Formulation II suppository has the highest peak, followed by Formulation III, IV and I. This means that Formulation II has the highest drug release rate compared to the other formulations. While the Formulation I has the lowest drug release rate.

Formulation II and III suppository have higher peak than Formulation I and IV. This means Formulation II and III have higher drug release rate compared to Formulation I and IV. Theoretically, the ideal formulation for suppository to have the highest drug release rate is 40% of PEG 1000 and 60% of PEG 6000. So, the ideal formulation used in this experiment should be the formulation III which contain 33.33% of PEG 1000 and 60% of PEG 6000. The higher the percentage the PEG 6000 used, the higher the drug release rate. This is because PEG 6000 will enhance the drug release. But, too high percentage of PEG 6000 will decrease the drug release rate instead of enhance it. Based on the results obtained from experiment, the suppository that shows highest release rate is from Formulation II. This may be due to some experimental errors occur.

Formulation I has the lowest drug release rate because the absence of PEG 6000 in the formulation. Although there is PEG 1000 in the formulation, it only has little effect on drug release. PEG 6000 has much more influence on drug release compared to PEG 1000.

Although formulation IV has the highest percentage of PEG 6000, it does not show the highest drug release rate. This is because too many PEG 6000 will cause the formation hydrogen bond between PEG and paracetamol. It requires the longer time to reach the highest value of drug release, as the suppository is the hardest. As a result, the drug release rate decreases.  

            These may be some errors occur in the experiment and lead to inaccurate result. Uneven stirring of the solution, unstable temperature, mistake in the suppository formation, impurities can all lead to the experimental errors.

5.What is the function of each ingredients that used in suppository formulation?

How the differences amount  of PEG 1000 and PEG 6000 will affect the physical characteristic of suppository formulation and the release of drugs from formulation?

Ingredient that we used in the paracetamol suppository formulation is paracetamol and PEG 6000, which paracetamol as the active ingredient while PEG 6000 as suppository  bases.In our formulation,we doesn’t used PEG 1000. During the manufacturing,PEG show easy release from the mold, high stability and no refrigeration is required during storage which it easily to solidify.

Commonly, formulation used of compounds of two or more molecular weights mixed in various proportions as needed to yield a finished product of satisfactory hardness and dissolution time. Different ratios of low and high molecular weight of PEG can be altered to alter the hardness of the suppositories. The more higher molecular weight of PEG, PEG 6000 will form more harder suppositories compared to lower molecular weight PEG, PEG 1000.So,as mention before our formulation only used PEG 6000,that’s why the suppository is solidify faster and become more harder.Since the water miscible suppositories dissolve in body fluids and need not be formulated to melt at body temperature, they can be formulated with much higher melting points and thus may be safely stored at room temperature. Formulation with higher  PEG 6000, will release drug more slowly and also brittle compared to formulation with lower amount of PEG 6000. This will affect the rate of absorption of drug into body.

Conclusion :

The effect of different composition of PEG 1000 and PEG 6000 in the suppository formulation can be observed through their physical appearance, drug releasing pattern and their ease of melt.

Reference :

1.      Physicochemical Properties of Pharmacy, Florence & Attwood, 3^rd Edition.

2.      Pharmaceutics, The Science of Dosage Form Design, Mecheal Aulton, 3^rd Edition.

Appendices