Preface

THIS WILL BE PUBLISHED PER CHAPTERS: PART 7/8.

During my final year of my bachelor of pharmacy, I had the joy of doing a project in pharmaceutics on topical corticosteroids. My colleague and I achieved a distinction for this project but we do admit that we can see some mistakes in our project. This project took us 6 months to accomplish and it mainly taught us about research, reading the literature and to attempt at making a pharmaceutics project. This was more of an introduction to a masters degree path and also taught us to work on our own and be supervised with an allocated supervisor. All in all, we learned a great deal and we were thankful for it.

Authors: Andréas L.P. Astier, Priyanka Naidoo

Supervisors: Professor R. Walker, Dr S.M. Khamanga

Location: Pharmaceutics Department, Rhodes University, Grahamstown, 6140, South Africa.

CHAPTER SIX

Discussion and Conclusion

6.1. Discussion

6.1.1. Dissolution

Dissolution tests are employed to establish drug API release characteristics of semi-solid formulations. The rationale for conducting these tests is that for a product to be therapeutically effective, the drug must be released from the product (68). A dissolution test may be considered as a critical step for the development and assessment of the quality of products linking to their safety and efficacy attributes (68).

The results of the study showed that the rate of drug release, over 180 minutes on day 0, from formulation 1, 2, 3 and 4 respectively was 60,77 %, 68,86 %, 46,25 % and 27,17 % mean percentage of API per cm2, see Figure 5.16. On day 28, the release of CBP from formulation 1, 2, 3 and 4 respectively was 6,14 %, 3,99 %, 3,10 % and 2,17 %, see Figure 5.22. Overall all the formulations decreased significantly after 7 days except formulation 1 that had a 27,03 % mean percentage of API per cm2. Formulation 1 soon followed a low percentage release just like the other formulations on day 14. Formulation 1, except on day 0, always released more CBP into the dissolution medium compared to the other formulations. The reasons for such was that formulation 1 had the lowest viscosity which played a role in the release of CBP into the medium solution. The viscosity in formulation 1 was due to the wrong use or too much use of surfactant such as sodium lauryl sulphate, which is an anionic surfactant and may have affected the aqueous cream. This affected the release of CBP. Formulation 2 had the wanted viscosity throughout the 28-day period and released CBP the highest on day 0 with 68,86 % mean percentage of API per cm2. The right use of surfactant and amount was utilized by using cetrimide, a cationic surfactant, in the aqueous cream. However, unlike formulation 1, formulation 2 plummeted to a low release of CBP after 7 days with a 7,85 % mean percentage of API per cm2. This questions the right use of surfactant over the wanted viscosity. Formulation 3 contained cetromacrogol, a non-ionic surfactant, which demonstrated a higher release of CBP than the standard formulation 4 throughout the 28-day period. However, by day 7, formulation 3 was releasing CBP poorly into the dissolution medium. All formulations 1, 2 and 3 released CBP better than the standard formulation 4 throughout the 28-day period. Formulation 4 on day 0 released CBP poorly with only 27,17 % mean percentage of API per cm2 compared to the other formulations and after 7 days, released very little of CBP.

This demonstrates that diluting Dovate® with aqueous cream and homogenizing in the pharmacy shows that it is a major factor of slowing down and restricting the release CBP. This would not cause the wanted therapeutic effect as there is not enough CBP to create the wanted pharmacological effect. Furthermore, the usage of all formulations would not cause the wanted therapeutic effect even after 7 days, let alone if the creams were prescribed for 2 weeks.

6.1.2. Dissolution medium

The dissolution medium used in our experiment was water (69). Water is not a good dissolution medium due to not having a good buffering capacity since its pH is very sensitive to the addition of any acidic or basic species (70). A buffer is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it and thus it is used to prevent changes in the pH of a solution (69, 70). If we add a strong acid or strong base to water, the pH will change. For instance, if an acid is added, the proton (H+) from the acid binds to neutral water molecules to form H3O+ raising the concentration of H+ (70). Any excipients or API in the semi-solid formulation could change the pH of the dissolution medium. A varying pH will change the dissolution rate of the formulation introducing errors in the experiment (69). Hence, keeping a constant and unchanged pH is an important aspect in a dissolution medium.

6.1.3. Air pockets

Air pockets can bring variation in the results due to the present gases. Air pockets misrepresent the area and volume occupied by the formulations inside the jar, which incorrectly represent the results. The air pockets that are in contact with the membrane, it would alter the results due to the surface area measured on the membrane would misrepresent the surface area that is directly in contact with the formulation. Hence, if there are air pockets, the formulation is not in contact with the membrane to diffuse through the membrane and into the dissolution fluid to create a concentration for the absorbance which will cause inaccuracy and false results. If air pockets are present at the membrane, a decreased concentration should be seen compared to what it should be.

6.1.4. Spreadability

The spreadability nature of semi-solid preparation is an important characteristic of dermatological conditions (59). A semi-solid preparation that can be spread easily over the wanted area and not over/under spread, is desired by patients which increases patient’s satisfaction of the semi-solid preparation. If over time the viscosity and spread changes from its original spread characteristics, it will influence the patient’s perception of the semi-solid preparation which may be negative.

A change in the distance of the semi-solid preparation over time could indicate a change of the rheological properties such as the viscosity, elasticity, thixotropy, and flowability which had been affected in some way within the semi-solid preparation (59). This insinuates instability characteristics of the semi-solid preparation due to the compound(s) changing, and hence the interaction within the semi-solid preparation is also changing from the normal and original interactions (59). It is clear in mind that if the distance did not change, it would indicate no changes of rheological properties within the semi-solid preparation, and hence no instability as the product remained the same.

For the four formulations tested, spreadability on the whole, showed slight variations. For formulation 1 spreadability decreased from 17.33mm on day 0 to 15.60mm on day 28. The decrease in spreadability could be due to a slight increase in viscosity which would cause the area calculated for spreadability to decrease as the formulation does not spread as easily as on the first day. Formulation 2 showed an increase from 7.23mm on the first day to 9.40mm on the last day. Formulation 3 displayed an increase from 11.63mm on day 0 to 12.37mm on the last day and finally, formulation 4 displayed an increase from 6.73mm on day 0 to 8.60mm on the last day. For these three formulations just mentioned, the spreadability increased. This could again be due to viscosity. The viscosity, in this case, should have decreased making the formulations less prone to spreading. Many semisolids display non-Newtonian behaviour when placed under strain. The formulations were left in a locker after each week after experimenting for the day. Upon standing, the formulations can increase in viscosity due to the lack of strain and shear thinning it encounters whilst standing untouched in the locker. The formulations are tested for spreadability at the beginning of the experiment before being submitted to any agitation. This, therefore, reflects the non-Newtonian behaviour of the formulations.

The above data is an objective assessment of spreadability. Spreadability, when assessed subjectively with a rating out of 10 (10 being highly spreadable), displayed slightly different results. For formulation 1, spreadability decreased from a 9 to an 8 by the end of the experiment on day 28. Formulation 2 increased from a rating of 6 to 7. Formulation 3 stayed the same at a rating of 7 and formulation four stayed the same as well at a rating of 6. Formulation one displayed a decrease which was in line with the objective data. Formulation two displayed an increase much like the objective data too but formulation three and four remained the same on day 0 and day 28 although the spreadability tests clearly showed an increase in spreadability. These results are based on the perception of the individual assessing them and although the may be similar to the conclusion drawn from the measured data, they cannot be trusted as there is no scientific basis to them.

The T-test was used statistically for the spreadability of the formulations. Formulation 1, 2 and 3 on day 0 were compared to the standard, formulation 4 on day 0. Formulation 1 and 3 on day 0 showed a significant change compared to the standard. Formulation 2 on day 0 compared to the standard was the only formulation to not have significantly changed on its spreadability. Formulation 1 and 3 on day 28 showed a significant change compared to the standard, formulation 4 on day 28. Formulation 2 on day 28 compared to the standard was the only formulation to not have significantly changed on its spreadability. Statistically, the significant changes show that the formulation mean distance in centimetres were different, with a certain degree of confidence, compared to the standard formulation. Formulation 2 had no significant changes throughout the whole 28 days compared to the standard and kept the ideal and wanted spreadability of the standard. Ideally, all formulations should have had a viscosity of formulation 2 and 4.

6.1.5. Assessment of formulations

Consumer preference for semi-solid products depends on various properties of the preparation, collectively known as the textural profile, which includes appearance, odour, extrudability (when applicable), initial sensations upon contact with the skin, spreading properties, tackiness, and residual greasiness after application (57, 58).

The formulations prepared for this experiment, all displayed generally pleasing aesthetics. Throughout the duration of the experiment, the formulations remained white, clean, microbe-free and sterile smelling. There was no to very little signs creaming, coalescence or microbial growth. the lack of microbial growth is due to the preservative, chlorocresol, that was incorporated into the formulations and also partly due to the preservative already contained in the commercial aqueous cream. All four formulations were smooth throughout the process and no grittiness was encountered. The only inconsistency that arose in texture was in formulation two on day 7 where a “chunkiness” appeared to have resulted under the top layer of cream. When the formulation was scooped with a spatula, then only was it noticed that there was a “cottage cheese” like appearance to the cream. This was resolved upon mixing but then reappeared on day 14. This result is due to an instability of the formulation. There is a possible interaction between charges in the formulation that has caused this effect. Since aqueous cream is non-ionic and cetrimide is cationic, an interaction between charges should not result. There may however be an interaction of charges between CBP and cetrimide.

On day 7, 14 and 28, there was a slight amount of cracking visible in formulation three. The formulation appeared to be weeping. This occurrence was difficult to discern and could even be mistaken for an inherent glossy nature of the formulation. This weeping or cracking is again due to incorrect formulation and due to charges between the surfactant and the CBP interacting. Aside from this, it could even be noted that there may not be enough surfactant in the formulation to result in proper emulsification hence the slight cracking. The use of surfactant impacts the stability of the cream by creating an emulsion and the use of the wrong surfactant can cause flocculation, cracking, coalescence and Oswald ripening.

As for the viscosity of the formulations, the viscosity was subjectively assessed. For formulation one, viscosity appeared to have increased over the 28-day period from a rating of 3 to 4. For formulation two, the viscosity increased from 6 to 7. Formulation three increased from 6 to 8 and for formulation four, the viscosity increased from 6 to 9. All formulations showed an increase. If viscosity was deduced as having increased for formulation one and having decreased for the other formulations, just by analysing the spreadability tests, then the analysis of viscosity here is skewed. This, however, is the issue when assessing any formulation subjectively.

To ascertain if there was a significant difference between each cream on day 0 and day 28, Chi-squared tests were conducted. Formulation one and four appeared to have significant changes whilst formulation two and three had no significant changes. This data appears to be an inaccurate reflection of the actual textural profile of these formulations because two and three appeared to display more instability than one and four. This result is an atonement to the lack of validity subjective data can incur.

As a last note on the assessment of the formulations, the manufacturing methods employed also affect the stability, viscosity, spreadability and contamination of these formulations. Homogenisation affect the viscosity of the formulations which thus impacts the spreadability of the formulations.

Statistically, the chi-square test showed that formulation 2 and 3 did not change at the textural profiling compared to formulation 1 and 4 (standard) which were significant.

6.1.6. Degradation and theoretical values

The degradation and theoretical values could be an interesting concept to predict formulations and their release of API into the medium. In a way, it acts as an expiry date, where beyond the release of 90% of the mean percentage of a certain API per cm2 could deem the formulation expired. A few problems arose such as; the need of a statistical approach to calculate at what points are part of the dissolution plateau, the statistical approach of accepting or rejecting of the percentage difference from theoretical to actual (%) needs to be clarified and specific, and the overall unpredictability of a formulation. As seen, it was surprising to us when on day 60 formulation 1, 2, 3 and 4 showed an average of 20,60 %, 4,10 %, 3,33 % and 2,66 % mean percentage of API per cm2 respectively where it was supposed to be 0,44 %, 0,15 %, 0,13 % and 0,12 % mean percentage of API per cm2. Day 60 demonstrate that formulation 1, 2, 3 and 4 mean percentage of API per cm2 were all above the mean percentage of API per cm2on day 28. Somewhere between day 28 to day 60, all the formulation started to release CBP more efficiently than previously. We can only speculate that some excipients or the aqueous cream itself cannot keep its integrity for up to 60 days and start changing in its rheology properties. A change in the rheology properties of an aqueous cream could be the reason for the different rate of the CBP release into the medium.

Formulation 1 is a good example of using the degradation equation concept, as for the first 28 days, the percentage difference from theoretical to actual (%) is between - 20,048 to + 18,626 % maximum difference. See Table 5.16. As said previously, up to how much of percentage difference from theoretical to actual (%) would the prediction be accepted? Would this concept work on other vehicle or dosage routes such as ointment, gels, shampoos, different excipients with different concentrations, other APIs, pH and other factors? Time is also an important factor, as seen on day 60, the actual percentage went higher than expected giving a difference of, for example, + 4580,68 % in formulation 1. At what time does the prediction become redundant?

6.1.7. Accumulation studies

Patients are required to use no more than 50 grams of cream per week (28, 29). That is 3,571 grams for each use twice a day (4, 16, 20). The accumulation study shows how much a patient actually needs to use to cause the wanted therapeutic effect. As time goes, more of the creams will have to be used as their dissolution plateaus decrease. Each formulation will differ depending on their average plateau release from their respective dissolution curve. See Table 5.21-24 and Figure 5.32. A red arrow will then show the time (days) when a patient would have run out of cream if they had a 200 gram CBP aqueous cream, see Table 5.25. As shown, formulation 1 will be used up to 9 days as formulation 1 had a generality of a higher percentage release of CBP into the dissolution medium, hence less cream is needed to reach the therapeutic level. Formulation 4, which was the dovate® standard, demonstrate the worst in regards with the release of CBP and hence was the first formulation to be used up just after 2 days and 12 hours (or after 5 usages).

However, we have no idea how much and how consistent patients spread their CBP aqueous cream. The severity of the disease, age, sex, race, gender, surface area are factors to consider. All usage should be within 2 weeks and not longer than the required time as the rheology properties will more than likely change which will change the release of CBP. Figure 5.33. demonstrate the curve include day 60, where previously shown, day 60 had a higher mean percentage of API per cm2. Hence, if there is a higher percentage release, then the patient would use less aqueous CBP cream. This is the reason why there is a dip in the graph (Figure 5.33.).

Ideally, all creams for as long as possible should be releasing 100 % of API into its environment, whether it has been diluted further with aqueous cream and homogenized in a pharmacy setting. 100 % release will always present with the wanted pharmacological effect and alleviate the symptoms of the condition which will produce patient satisfaction.

6.2. Conclusion

The effect of diluting the formulations and the standard formulation containing Dovate® with aqueous cream and homogenizing in a pharmacy setting showed that it was a major factor of slowing down or restricting the release CBP. Excipients have a role within the formulation and can influence the release of CBP into the wanted media, for example, formulation 3 had cetromacrogol where compared to formulation 1 and 2, released the least CBP, or sodium lauryl sulphate within formulation 1 helped in releasing CBP better than formulation 2 and 3 but at the cost of an unwanted viscosity. None of the formulations was releasing adequately after 7 days. This would not cause the wanted therapeutic effect as there is not enough CBP to create the wanted pharmacological effect.

The T-test and Chi-test were used statistically for the spreadability and the textural profiles of the formulations. Formulation 2 on day 0 and 28 compared to the standard was the only formulation to not have significantly changed on its spreadability. Formulation 2 and 3 statistically did not change at the textural profiling.

The degradation and theoretical values could be an interesting concept to predict formulations and their release of API into the medium. However, many studies need to be done to create a more accurate prediction of the semi-solid formulations.

The accumulation studies contain many factors such as the amount of how much and how consistent patients spread their CBP aqueous cream. The severity of the disease, age, sex, race, gender, surface area are factors to consider. It is interesting when the percentage release of API is not 100 % of how much a patient actually needs to apply for a pharmacological effect to occur, these put the accumulation studies up to perspective in regards with the CBP percentage release.

6.3. Further Studies

The need for a statistical approach to calculate at what points are part of the dissolution plateau is essential, a method of such should be created. The statistical approach of accepting or rejecting of the percentage difference from theoretical to actual (%) needs to be clarified and specific, an equation should be used. The overall unpredictability of a formulation should be studied, especially on different factors. Would this concept work on other vehicle or dosage routes such as ointment, gels, shampoos, different excipients with different concentrations, other APIs, pH and other factors? Time is also an important factor, as seen on day 60, the actual percentage went higher than expected giving a difference of, for example, + 4580,68 % in formulation 1. At what time does the prediction become redundant? We have no idea how much and how consistent patients spread their CBP aqueous cream. The severity of the disease, age, sex, race, gender, surface area are factors to consider.

6.4. Funding and Conflict of Interest

This study was not paid by sponsors and there was no financial interest in its outcome. We do not own the drug or device being tested and thus we have no financial interest in the outcome of the study. No payments were made, the funds used were from Rhodes University to cover the expenses of the study and related academic and research activities. The investigators do not have any financial interest in the outcome of the study.

Published 6th August 2019. Last reviewed 30th December 2021.

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