PRACTICAL 4 : Experiment 3 - Uniformity of weight of tablets and capsules

Objectives

To ensure the consistency of dosage units, each unit in a given batch should contain the active drug within a narrow range around the label claim.

INTRODUCTION

When the quality of the drug products are reliable, the safety and efficacy of drug products can be guaranteed. Usually tablets and capsules must be tested after to ensure the requisite quality. Like all other dosage forms, tablets and capsules are subjected to those pharmacopoeial standards which deal with “added substances” with respect to their toxicity and interference with analytical methods. However, there are a number of procedures which apply specifically to tablets and capsules, and which are designed to ensure they exerts its full pharmacological actions and to determine the uniformity of physical properties which can be found in the British Pharmacopoeia and United Pharmacopoeia.

MATERIAL AND APPARATUS

20 tablets, 20 capsules and weighing balance

Tablets

Experimental method:

1.      20 tablets are weighed previously. The average weight is determined.

2.      The tablets are weighed individually and for each tablet is determined, the percentage deviation of its weight from the average weight.

3.      The deviation of individual weight from the average weight should not exceed the limits given below.

Average weight of tablet	Deviation (%)	Number of tablets
Less than 80 mg	+ 10.0 + 20.0	Minimum 18 Maximum 2
80 mg to 250 mg	+ 7.5 + 15.0	Minimum 18 Maximum 2
More than 250 mg	+ 5.0 + 10.0	Minimum 18 Maximum 2

Capsules

Experimental method:

1.      20 capsules are selected at random.

2.      One capsule is weighed. The capsule is opened and the contents are removed as completely as possible.  The emptied shells are weighed. The net weights of the contents are determined by subtracting the weight of the shells from the weight of the intact capsule.

3.      The procedure is repeated with other 19 capsules.

4.      The average net weight is determined from the sum of the individual net weights.

5.      The percentage deviation is determined from the average net weight for each capsule. The deviation of individual net weight should not exceed the limits given below:

Average net weight of capsule	Deviation (%)	Number of tablets
Less than 300 mg	+ 10.0 + 20.0	Minimum 18 Maximum 2
300 mg or more	+ 7.5 + 15.0	Minimum 18 Maximum 2

RESULTS AND CALCULATION :

A. TABLET

NO.	MASS (g)	Deviation (%)
01	0.6568	1.0151
02	0.6517	0.2307
03	0.6467	0.5383
04	0.6505	0.0461
05	0.6613	1.7072
06	0.6672	2.6146
07	0.6684	2.7991
08	0.6655	2.3531
09	0.6619	1.7994
10	0.6462	0.6151
11	0.6651	2.2916
12	0.6484	0.2768
13	0.6477	0.3845
14	0.6545	0.6613
15	0.4479	31.1135
16	0.6601	1.5226
17	0.6530	0.4306
18	0.6803	4.6293
19	0.6673	2.6300
20	0.7032	8.1513

Average mass of tablets

g

Average mass is more than 0.250g or 250mg

Deviation (%)

For example:

DISCUSSION:

For tablets, the average mass is 650.2mg or 0.6502g which is more than 0.250g or 250mg. So, the deviation (%) of the tablets should not exceed the limits given below;

Average weight of tablet	Deviation (%)	Number of tablets
More than 250 mg.	 5.0	Minimum 18
	 10.0	Maximum 2

As we can see from the results of the deviation (%) of the tablets, there is a tablet weighed 0.4479g that having ±10 % deviation which is obeyed the limits above as it should have at maximum number of 2 tablets. There is a tablet weighed 0.7320 g that is out of the range of the deviation. It scored 31.1135%. This may be due to the analytical error of the weighing balance. It may be caused by the hypersensitivity of the balance itself. It sometimes takes a few minutes to function properly and become more sensitive to any disturbance throughout the process such as vibration or even air flow within the area.

The rest of tablets (18 tablets) are within the range of 5 % of deviation which obeys the limit above to have minimum number of 18 tablets only.

The deviation of the mass of tablets may be explained by the technical reasons. They are differences in bulk densities, particle size distribution during compression, flowing properties of the powder, the speed of tableting machine, the pressure used in compression and the type of machines used in tableting also contributes to the deviation of mass in tablets.

B. Capsules

NO.	WHOLE CAPSULES (g)	CAPSULE ONLY (g)	CONTENT (g)	DEVIATION (%)
01	0.3635	0.0645	0.2990	4.5455
02	0.3548	0.0602	0.2946	3.0070
03	0.3458	0.0572	0.2886	0.9091
04	0.3469	0.0606	0.2863	0.1039
05	0.3551	0.0566	0.2985	4.3706
06	0.3433	0.0614	0.2819	1.4336
07	0.3543	0.0688	0.2855	0.1748
08	0.3800	0.0690	0.2910	1.7483
09	0.3601	0.0654	0.2947	3.0420
10	0.3348	0.0629	0.2719	4.9301
11	0.3483	0.0685	0.2798	2.1678
12	0.3528	0.0662	0.2866	0.2098
13	0.3521	0.0683	0.2838	0.7692
14	0.3543	0.0689	0.2854	0.2098
15	0.3448	0.0679	0.2769	3.1818
16	0.3548	0.0671	0.2877	0.5944
17	0.3447	0.0664	0.2783	2.6923
18	0.3520	0.0681	0.2839	0.7343
19	0.3543	0.0683	0.2860	0
20	0.3459	0.0669	0.2790	2.4476

Average mass of capsules

g

Average mass is less than 0.3000 g or 300 mg

Deviation (%)

For example:

DISCUSSION

For capsules, the average mass is 286 mg or 0.2860 g which is less than 0.300g or 300mg. So, the deviation (%) of the tablets should not exceed the limits given below;

Average net weight of capsule	Deviation (%)	Number of tablets
Less than 300 mg.	 10.0	Minimum 18
	 20.0	Maximum 2

As we can see from the results of the deviation (%) of the capsules, most of the contents of the capsules are having deviation of less than 10 % which means the mass of capsules are uniformly distributed. This may be due to the better usage of weighing balance. The weighing balance has lesser analytical errors and increased the accuracy as the time goes by.

There are some possible causes of improper distributions. It may be due to the error of the capsule filling machine or the bulk density during capsules filling.

Conclusion

The tablets did not follow the standard of uniformity of weight though the all the capsules followed the standard uniformity of weight. This might be due to the error discussed in the discussion.