Practical 4 - Dosage performance tests (Dissolution)

Objective:

To investigate the percentage amount of ibuprofen dissolved

Introduction:

The dissolution test for tablet is done to ensure that the tablet dissolution rate is at the optimum and the desired value. Besides that, tablet dissolution test allows us to determine the bioavailability of the active ingredient of the drug in tablet form in the body to give the desired pharmacological effects effectively. We can also determine the specific pH value at which the tablet dissolves best. If the dissolution of the tablet is not at its optimum level as predicted, then, we will have to reformulate or find out what errors have been made during the pre-formulation procedure of the tablet.

Procedure:

1. The dissolution vessels were filled up with buffer solution to 900mL mark. The temperature was set to 37°C.

2. The temperature of the dissolution medium was kept in check to ensure the temperature was at 37 ± 0.5°C.

3. One Ibuprofen tablet was placed into each dry basket assembly.

4. The stirring speed was set to 150rpm. Then, the basket assembly was lowered into position in the vessel and the operation was started.

5. 10mL samples of the dissolution medium from each vessel were withdrawn for analysis after 30 minutes and the solution was filtered using suitable filter. Sampling was done from middle point between the surface of the dissolution medium and the top of rotating basket, and not less than 10mm from the wall of the vessel. The volume of aliquot withdrawn for analysis was replaced with the same volume of same dissolution medium.

6. A standard solution of ibuprofen was prepared by diluting 10mg of ibuprofen reference standard to 50ml with dissolution medium.

7. 2.0ml of sample solution and 2.0ml of standard solution were diluted to 25ml with dissolution medium in separate volumetric flasks.

8. The absorption of both solutions was measured in a 1cm cell at a wavelength of 221nm.

9. The percentage amount of ibuprofen dissolved was calculated using the following formula:

At/As    X     W/50     X     2/25    X     P    X     900    X    25/2    X    100/200

Where,

At = absorbance of sample solution

As = absorbance of standard solution

W = weight of ibuprofen reference standard used

 P   = purity of ibuprofen reference standard

10. From the result obtained, the tablet compliance with the requirements of the United States    Pharmacopoeia was determined.

     USP limits : Not less than 75% of the stated amount of ibuprofen dissolved in 30 minutes.

Results:

At = 0.859

As = 3.847

Percentage amount of ibuprofen dissolved:

At/As    X     W/50     X     2/25    X     P    X     900    X    25/2    X    100/200

0.859/3.847   X     10/50     X     2/25    X     98/100    X     900    X    25/2    X    100/200 = 19.69%

Discussion:

            From the calculated value, the percentage amount of ibuprofen dissolved is 19.69% . The tablet does not comply with the requirements of United States of Pharmacopoeia as the percentage is less than 75%. This indicates that there are errors made during conducting this experiment.

            One of the main errors is the expiry date of the sample of ibuprofen tablet. The ibuprofen sample may have expired and this has reduced the quality of the tablet. The ingredients must have become unstable and did not dissolve properly. Thus, this may have greatly affected and resulted in the above poor dissolution rate and absorption of wavelength during the measurement using the spectrophotometer.

Besides, the stirring speed may not have reached 150 rpm. This will cause the dissolution rate to be slow and the low speed could have affected the dissolution rate. Moreover, the temperature of the dissolution vessel might be one of the factors. We did not monitor the temperature which must be maintained at 37°C with ± 0.5°C. Low temperature may cause poor dissolution while high temperature may alter the composition of the ibuprofen tablet.

Furthermore, the presence of dissolved gas in the dissolution medium or buffer solution might lead to inaccuracy of results by slowing down the dissolution rate. The syringe filter used may absorb some of the sample during withdrawing of sample. This will reduces the percentage of dissolved ibuprofen for analysis. Thus, less ibuprofen sample was detected.

            Therefore certain precautions must be taken to ensure the accuracy of the results. First, the sample must be in good condition and the expiry date of the tablet should be checked before use. We also must make sure the dissolution vessel is calibrated before used so that we can obtain accurate results. Besides, we must always double check the setting of temperature, stirring speed and time required for stirring process to avoid unnecessary errors. To prevent the presence of dissolved gas in the dissolution medium or buffer solution, it is advisable to put the solution in ultrasonic water bath.

Conclusion:

The percentage amount of ibuprofen dissolved is 19.69%. This value is less than 75%, therefore the tablet does not comply with the requirements of United States Pharmacopoeia.

References:
1. http://www.pharmainfo.net/Dissolution/dissolution-testing-various-dosage-forms
2. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3160163/