Formulation of Paracetamol Suppositories PDF

Preview

Summary

Lab report of the formulation lab (of paracetamol suppositories) from the drug discovery case...

Description

Abstract This study was aimed at comparing three commonly used bases and determining which base would be most appropriate for the formulation of 10 suppositories containing 250mg paracetamol. The bases compared were: Witepsol H15, Theobroma oil and a polyethylene glycol (PEG) mixture (95% PEG 1000 and 5% PEG 4000). Suppositories containing paracetamol were made using all three bases and were compared using 4 post formulation tests; uniformity of mass, softening time, disintegration time and uniformity of content via HPLC. The batch made using Witepsol H15 was the only batch to have passed all four post formulation tests, whilst the batch made using Theobroma oil passed all tests except uniformity of content. The batch made using PEG passed the uniformity of mass and disintegration time tests, however failed the softening time and uniformity of content tests. It was therefore decided that suppositories made using Witepsol H15 were the only suppositories that could provide a safe and accurate dose and was therefore used to make the final product.

Introduction Background on acetaminophen Acetaminophen also called Paracetamol is a commonly used analgesic and antipyretic agent that is mainly sold over the counter. Its exact mechanism of action is still unclear although it’s thought to inhibit prostaglandin synthesis in the central nervous system and to a lesser extent through peripheral action of blocking pain impulse generation. [1] [2] In producing antipyretic effect, paracetamol is thought to act centrally on the hypothalamic heat regulation centre to produce peripheral vasodilation that leads to increased blood flow through the skin, sweating and heat loss. [1] [3] Paracetamol has a molecular weight of 151.2g/mol and Log P of 0.46 making it very soluble with a water solubility at 25 degrees of 14000mg/l. It’s therefore readily absorbed from the gastro intestinal tract reaching its peak plasma concentration within 30 – 60 minutes after oral ingestion, (Rang) and 2- 4 hours after rectal administration. It has a therapeutic plasma half-life of between 1-4 hours and is primarily metabolized in the liver. It’s mainly excreted in the urine as glucuronide and sulphate conjugates with 2-3% as unchanged drug. [1] Why suppositories? Suppositories for paediatrics offer an advantage over oral administration by avoiding drug loss due to nausea and vomiting. Rectal administration can be particularly useful where children are unwilling to swallow tablets or oral solutions. Furthermore, rectal administration of drugs avoids first pass metabolism as absorption in the middle and lower part of the rectum is direct into general circulation. [4] [5] The disadvantages of using suppositories include the inconvenience of having to insert the suppository into the rectum as it can be quite uncomfortable. Also, rectum absorption is erratic and unpredictable as it’s dependent on age, weight and bowel movements of the individual. Additionally, the drug can easily leak out and be expelled while it awaits absorption, as the absorption rate is slow via passive diffusion over a reduced surface area in the rectum compared to a larger surface area in the small intestines if the drug was administered orally. Purpose of the exercise Suppositories are a drug delivery system where, in this case paracetamol, is incorporated into an inert ‘base’. Ideal characteristics of a base include; melting at or just below body temperature or readily dissolvable in rectal fluids, solidify quickly after melting, the ability to

be easily moulded and removed from the mould, chemically stable even when molten, release the active ingredient readily and perhaps most importantly – be non-toxic. [6] Hence the objective of this study was to compare between three commonly used bases by carrying out a series of post formulation tests and decide which would be the most appropriate for the formulation of a batch of ten 250mg paracetamol suppositories. The three bases that were tested were: Theobroma oil, Witepsol H15 and a polyethylene glycol (PEG) mixture (95% PEG 1000 and 5% PEG 4000).

Methods The suppositories were made using the melt mould technique [7]. Clean suppository moulds of 15 grain were used to produce suppositories of roughly one gram – a suitable weight for paediatrics. Theobroma oil was the only base that required lubrication, therefore the mould was lubricated with liquid paraffin. The moulds for each of the excipients were calibrated using placebo suppositories using the procedure as described below - the only difference being no active ingredient was included. Witepsol H15 Enough Witepsol base and paracetamol were weighed out to make an unavoidable wastage to ensure that at least 25 perfect suppositories could be made. Therefore, enough Witepsol and paracetamol was calculated to make 40 suppositories. 36.1g of Witepsol and 10g of paracetamol were weighed out. The Witepsol was melted at 53°C in a porcelain bowl, until two thirds had melted. The paracetamol was ground using a pestle and mortar to reduce the particle size. The paracetamol was added to the melted Witepsol and mixed. If there were any large ‘clumps’ of paracetamol powder present in the mixture it was ground down using the pestle. The mixture of paracetamol and Witepsol was heated and stirred until all the paracetamol was distributed evenly in the mixture. The mixture was stirred until the base had started to set at which point it was poured into the suppository moulds, ensuring each mould was slightly overfilled. The mould-mixture was allowed to cool and set before removing each suppository. Temperatures were measured using a glass thermometer. Theobroma oil Enough Theobroma oil and paracetamol were weighed out to make an unavoidable wastage to ensure that at least 25 perfect suppositories could be made. Therefore, enough Theobroma oil and paracetamol were weighed out to make 40 suppositories. 38.5g of Theobroma oil and 10g of paracetamol were weighed out. Two thirds of the Theobroma oil was melted at 36°C in a porcelain bowl in a water bath, at this point the paracetamol powder was added and stirred. If any large ‘clumps’ of paracetamol powder were present in the mixture it was ground down using the pestle. The mixture of paracetamol and Theobroma oil was heated and stirred until all the paracetamol was distributed evenly in the mixture. The mixture was stirred until the base had started to set, once this happened it was poured into the suppository moulds, ensuring each mould was slightly overfilled. The mouldmixture was allowed to cool slightly and was then placed in a fridge to allow to set properly, before being removed. Polyethylene Glycol (PEG) A mixture of PEG 1000 (95%) and PEG 4000 (5%) was used to form the base used for these suppositories. Enough PEG and paracetamol were weighed out to make an unavoidable wastage to ensure that at least 25 perfect suppositories could be made. Therefore, enough

PEG and paracetamol were weighed out to make 40 suppositories. The total amount of base required was 45.1g therefore 42.8g of PEG 1000, 2.3g of PEG 4000 and 10g of paracetamol was weighed out. The mixture of PEG was melted in a porcelain bowl at 50℃. Once two thirds of this was melted the paracetamol powder was added and stirred. If any large ‘clumps’ of paracetamol powder were present in the mixture it was ground down using the pestle. The mixture of paracetamol and Theobroma oil was heated and stirred until all the paracetamol was distributed evenly in the mixture. The mixture was then heated at 50℃ until all of the paracetamol had dissolved into the mixture and was distributed evenly. The mixture was stirred until the base had started to set, once this happened it was poured into the suppository moulds, ensuring each mould was slightly overfilled. The mould-mixture was allowed to cool until the suppositories had set, at which point they were then removed. The amount of base required was calculated using the formula: [7] Amount of base = (Nxy) - (NxD)/(DV) Where N = no. of suppositories to be made Y = mould calibration of the base being used D = dose of active ingredient DV = displacement value To see the calculation for each base please refer to the appendix. Post formulation tests Four post formulation tests were carried out on each of the three batches of suppositories. The tests comprised of: uniformity of content using HPLC, uniformity of weight, softening time and disintegration time. Each test was completed using 3 suppositories from each batch. Uniformity of content using HPLC Analysis: Standards of paracetamol with the following concentrations; 25 mcg/ml, 50 mcg/ml, 75 mcg/ml and 100 mcg/ml were made by diluting a pure sample of paracetamol powder in methanol. These standards were used to obtain a calibration plot which can be seen in figure … in the appendix. 3 suppositories from each batch were separately heated and dissolved in 50ml methanol, following this, serial dilutions were made of each sample to achieve a final dilution concentration of 50mcg/ml that was used in the HPLC analysis and compared against the 50mcg/ml standard. Uniformity of mass: Each of the three samples from each batch were weighed using a balance that measured to the nearest milligram. Softening time and disintegration tests: Both tests were carried out using the suppository tester SDT 1000 with an attachment for measuring the softening time.

Results Visual examination All suppositories were observed as an intact unit. All batches of suppositories, made using all three bases; had no signs of cracks, dimples or sink holes and all suppositories were solid at room temperature. All suppositories were perfectly symmetrical, apart from 6 suppositories made using Theobroma oil. Witepsol H15 Table 1 below shows the uniformity of mass of 10 suppositories containing paracetamol made with Witepsol. The mean mass of the sample was 0.989. The limits of deviation defined by the British pharmacopoeia (BP) [8] were 5% either side of the mean. The relative standard deviation of 2.25 % was within the 5% limit of deviation and therefore the suppositories passed the uniformity of mass test.

Table 1 - Uniformity of mass results for 10 suppositories containing paracetamol, made using Witepsol H15

Table 2 below shows the softening time results of 3 suppositories made using Witepsol. The mean softening time was 11.68 minutes. The limits of deviation were 95-105% of the mean. The relative standard deviation of 2.92 % was within the 5% limit of deviation and therefore the suppositories passed the softening time test.

Table 2 - Softening time results for 3 suppositories containing paracetamol made from Witepsol H15

Table 3 below shows the disintegration time of 3 suppositories made using Witepsol. All three suppositories melted within the BP limit [8] of 30 minutes for fat-based suppositories therefore the suppositories passed the disintegration test.

Table 3 - Disintegration test results for 3 suppositories containing paracetamol made from Witepsol H15

Table 4 below shows the uniformity of content test for 3 suppositories made using Witepsol. All suppositories were within the limits of deviation outlined by the BP, [8] which was 95105% of the stated amount of paracetamol. Therefore, the batch passed the uniformity of content test.

Table 4 - shows the uniformity of content results for three suppositories containing paracetamol, made using Witepsol H15

Polyethylene Glycol (PEG) Table 5 below shows the uniformity of mass of 10 suppositories containing paracetamol made with PEG. The mean mass of the sample was 1.38. The limits of deviation defined by the BP were 5% either side of the mean. The relative standard deviation of 2.46 % was within the 5% limit of deviation and therefore the suppositories passed the uniformity of mass test.

Table 5 - Uniformity of mass results for 10 suppositories containing paracetamol made using polyethylene glycol

Table 6 below shows the softening time results of 3 suppositories made using polyethylene glycol. The mean softening time was 16.33minutes. The limits of deviation were 95-105% of the mean. The relative standard deviation of 9.85 % exceeded the 5% limit of deviation and therefore the suppositories failed the softening time test.

Table 6 - Softening time results for three suppositories containing paracetamol, made using PEG

Table 7 below shows the disintegration time of 3 suppositories made using PEG. All three suppositories melted within the BP limit [8] of 60 minutes for water-soluble suppositories therefore the suppositories passed the disintegration test.

Table 7 - Disintegration test results for three suppositories containing paracetamol made from a PEG mixture.

Table 8 below shows the uniformity of content test for 3 suppositories made using Polyethylene glycol. All 3 of the suppositories fell outside the limits of deviation outlined by the BP [8], which was 95-105% of the stated amount of paracetamol. Therefore, the batch failed the uniformity of content test.

Table 8 - shows the uniformity of content results for three suppositories made using Polyethylene glycol.

Theobroma Oil Table 9 below shows the uniformity of mass of 10 suppositories containing paracetamol made with Theobroma oil. The mean mass of the sample was 1.28. The limits of deviation defined by the BP [8] were 5% either side of the mean. The relative standard deviation of 1.66% was within the 5% limit of deviation and therefore the suppositories passed the uniformity of mass test.

Table 9 - Uniformity of mass results for 10 suppositories containing paracetamol made using Theobroma oil.

Tabl e10s ho wst her es ul t sf ort hes of t eni ngt i met es ton3s uppos i t or i esmadeus i ng Theobr omaoi l .Themeans of t eni ngt i mewas10. 20mi nut es .Thel i mi t sofde vi at i on we r e95105% o ft hemean.Ther e l at i ves t andar ddevi at i onof1. 67% waswi t hi nt he5% l i mi tofde vi at i o nt her ef or et hebat c hpas s eds of t e ni ngt i met es t .

Table 10 - Softening time results for three suppositories containing paracetamol, made using Theobroma oil.

Table 11 below shows the disintegration time of 3 suppositories made using Theobroma oil. All three suppositories melted within the BP [8] limit of 30 minutes for fat-based suppositories therefore the suppositories passed the disintegration test.

Table 11 - Disintegration test results for three suppositories containing paracetamol, made using Theobroma oil.

Table 12 below shows the uniformity of content test for 3 suppositories made using Theobroma oil. All 3 of the suppositories fell outside the limits of deviation outlined by the BP [8], which was 95-105% of the stated amount of paracetamol. Therefore, the batch failed the uniformity of content test.

Table 12 - shows the uniformity of content results for three suppositories made using Theobroma oil.

Discussion Summary of results The batch Witepsol H15 suppositories passed all four of the post formulation tests. The suppositories made using polyethylene glycol (PEG) passed the uniformity of mass and disintegration time tests, however failed the softening time and uniformity of content tests. Suppositories made using Theobroma oil passed the uniformity of mass, softening time and disintegration tests however, failed the uniformity of content test.

Uniformity of mass The British pharmacopoeia (BP) [8] recommended weighing 20 solid dosage units with the acceptance criteria being not more than 2 units should deviate from the average mass by more than 5% and none should deviate by 10% however, given constraints on time and resources only 10 suppositories from each of the bases were weighed. Therefore, the acceptance criteria used was no more than 1 suppository should deviate from the average mass by 5% and no suppositories should deviate by 10%. The results from the test indicate that all moulds were well filled and the mixture was homogenous. Also, the presence of axial cavities and air bubbles caused by poorly adjusted mechanical stirring was unlikely. Since all batches passed due to having relative standard deviations within the limits of deviation outlined by the BP [8], with their mean mass being close to 1 gram, it’s likely that the paracetamol content is roughly the same in all suppositories of each batch.

It cannot be said the formulation of each batch was stable due to measurements and the test being carried out one week after the formulation of the suppositories, as this may not have been long enough to see any noticeable effects due to degradation. Also, measurements were only taken on one occasion so therefore no comparisons could be made to determine any changes in mass indicative of degradation. Further testing would be recommended to monitor for any changes in mass over time. Softening time The softening time test is designed to measure the time taken for a suppository to melt at 37°C. This test is more applicable to lipophilic bases, as release of drug is dependent on the suppositories’ ability to melt at the temperature within the rectum, whereas suppositories made using water-soluble bases rely upon the dissolution within rectal fluids. There were no acceptance criteria specified by the BP, possibly due to varying melting points of different bases, which would affect the time it takes for the suppository to soften. Therefore, it was decided that a relative standard deviation of more than 5% would fail the sample, to reduce the variation in the softening time and produce a reliable value. The results for both Witepsol H15 and Theobroma oil were expected due to their respective melting points of 33.5-35.2 ºC [9] and 30-36 ºC [2]. The results indicate that suppositories made using either base would melt at the temperature within the rectum giving adequate drug release. Also, their relative standard deviations of 2.92 % and 1.67 % respectively, would indicate that the result was reliable due to a low variance in softening time. As stated earlier this test was less applicable to the PEG mixture due to it being a watersoluble base, however its relative standard deviation of 9.85 % caused it to fail the test, an explanation for this observation could be inadequate mixing of both PEG 1000 and PEG 4000 when producing the mixture. Disintegration test The disintegration test is designed to measure whether suppositories disintegrate or soften within a prescribed time when placed in an immersion fluid [10]. The BP [8] outlined the prescribed time for fat-based suppositories as 30 minutes and 60 minutes for water-soluble based suppositories. [8] The results indicated that suppositories made using all 3 bases would melt or dissolve within a patient’s rectum in an appropriate amount of time and therefore would be less likely to inconvenience a patient by taking too long to melt or dissolve and would release all the API in an appropriate time, making it available for absorption in the rectum. This also makes it less likely that the suppository and its contents would be expelled from the anus due to the defecation reflex – which would be more likely the longer the solid suppository stays within the rectum as noted by Gross et al. [11] Given the previous statement Witepsol H15 would be the most desirable of the three bases due to having the lowest mean disintegration time of 19.33 minutes with also the lowest relative standard deviation of 1.16 % compared to the mean disintegration times of PEG and Theobroma oil of 19.65 minutes and 19.60 minutes respectively and their respective relative standard deviations of 2.50% and 8.84% as noted in tables 3, 7 and 11 in the results section. Uniformity of Content test

The uniformity of content test was designed to show how much API was in each suppository and whether the dosing was consistent within the batch. The BP outlined a monograph for paracetamol suppositories and specified that paracetamol content should be within 95105% of the label claim. Suppositories made using Witepsol H15 were the only suppositories within BP limits, they also had a low relati...