The thickness Test for tablets is one of the most frequently & commonly used tests for tablets which is performed during the tablet compression operation.
A thickness test for tablets is initially performed after line clearance to ensure that the thickness of individual tablets is within the specified range as mentioned in BMR and later on tablet thickness is checked throughout the compression operation at specified time intervals.
What Is a Tablet Thickness Test?
The test that is used to measure how thick the tablet is, known as the tablet thickness test.
Tablets are manufactured using different shapes of tooling and an important challenge is the control of thickness of all individual tablets using a specific shape of tooling.
For example If we compress the tablets using oval-shaped tooling then we know that all the tablets will have an oval shape but the thickness may vary depending on various factors which we will read later in this article.
We measure the thickness of the tablets by taking some sample tablets to ensure that tablet thickness is within a specified range.
Equipment Used To Measure Tablet Thickness
The tablet thickness is measured in millimetres and the following instruments are used to measure tablet thickness,
- Vernier Caliper
- Micrometre
- Thickness Gauge
How To Perform a Thickness Test For Tablets?
Measuring tablet Thickness is a very simple process which can be done by using any of the above-mentioned instruments.
The most commonly used instrument to measure tablet thickness is the vernier calliper.
The vernier calliper gives reading in millimetres and it is available both in digital display and manual reading.
To measure the tablet thickness simply place the tablet in between the jaws and slide the scale jaw to press the tablet against the stationary jaw.
The reading on the display is noted and it is the actual thickness of the tablet.
Factors Affecting Tablet Thickness
The thickness of tablets is mainly affected by the following factors,
- Tablet Weight
- Die Filling
- Granules Size
- Tablet Hardness
- Tooling
Tablet Weight
Tablet weight is directly related to the tablet thickness, which means if weight is increased, thickness is also increased and vice versa.
The weight of the tablet is dependent on die filling volume & granule size.
Die Filling Volume
Die filling volume means filling of dies with powder or granules to compress the tablets.
Die filling volume is directly related to tablet weight so If die filling volume is not uniform the thickness of tablets will not be the same.
Granules Size
- The size of granules is another important factor which is indirectly related to the tablet thickness. If granule size is not uniform, die filling will be affected and the weight of the tablet will not be uniform, so we may observe variation in tablet thickness.
Tablet Hardness
Tablet hardness is directly proportional to the applied pressure using compression wheels meaning if we apply more pressure hardness is increased & vice versa.
If we keep all other factors constant i.e tablet weight & die filling volume, tablet thickness again may vary depending upon the tablet hardness or applied compression force.
If tablet hardness is increased tablet thickness is decreased and if tablet hardness is decreased tablet thickness is increased.
Machine Tooling
Variation in tablet thickness may also be observed if our compression machine tooling is not in good condition.
There may be variation in punch length due to excessive usage of tooling, which may decrease due to friction.
If the length of any lower punch is decreased it may result in higher tablet weight due to increased die filling and results in increased tablet thickness.
Tablet Thickness Limit USP
The thickness test is a non-official test for tablets so USP does not specify certain values for tablet thickness. In simple words, we do not have any tablet thickness limit provided by USP.
Tablet thickness is controlled by the in-house specifications and is usually controlled at the range of ±5 % from standard values.
Why Do We Perform a Thickness Test For Tablets?
Thickness test for tablets is performed in pharmaceutical industries due to the following main reasons.
- To Ensure Smooth Blister Packaging
- To Ensure Accurate Tablet Count
- As An Indicator Of Tablet Defects
To Ensure Smooth Blister Packaging
Tablets after compression are delivered to the blistering section if the coating is not the requirement and if tablet coating is the requirement then after tablet coating,tablets are blistered using specified tooling.
The blister machine tooling is designed according to the tablet weight & dimensions and tablet thickness plays an important role during blister tooling design.
If tablet thickness is out of the specified range it will result in problems during blister packaging.
Suppose that some tablet thickness is out of range from the upper limit value, meaning if the upper limit was 5.70 mm and the detected tablets thickness is 6.10 mm.
The tablets having out-of-range thickness will not properly fit inside the blister pocket and will stick to sealing plates when they are pressed during sealing of foils.
The sticking depends on how much individual tablets vary in thickness from the standard value; if there is a significant difference in tablets thickness, the table may even melt or burn when coming in contact with hot sealing plates.
If there is a small difference even then you can see a sticking mark on the surface of the blister & when we remove the tablet from the blister pocket its surface is also damaged.
If one tablet thickness is out of range due to which sticking occurs and we have to pack 10 tablets in a blister, the whole blister will be rejected.
Because of the above-mentioned reason we measure the thickness of individual tablets at specified time intervals to ensure that all the tables are compressed within the specified range of thickness.
To Ensure Accurate Tablet Count
Some tablets are packed in glass or plastic jars or bottles and have a specified number of tablets in a jar or bottle.
If tablet thickness is not uniform the number of tablets per jar or bottle may be disturbed.
Suppose we fill 100 tablets in a jar having 50 ml capacity and if tablet thickness is out of range at the upper limit then the jar will be filled with less number of tablets because more thich tablets occupy more space.
Indication Of Defect
The measurement of tablet thickness during tablet compression operation provides dual control over critical parameters like tablet weight & hardness.
If a batch of tablets is under compression after all the initial parameter checking, all are in range. In-process tests for tablets are routinely monitored after specified time intervals and all are satisfactory.
Suddenly the machine operator finds that the thickness of one tablet is out of range at the lower limit of the provided value, meaning its lower limit was 5.70 mm and the detected tablet thickness was 5.20mm.
The machine was stopped & during investigation, it was observed that this defect occurred as a result of low tablet weight due to improper die filling.
Improper die filling was due to the sticking of some powder inside the die bore.
In the same way,less thick tablets may be compressed due to overpressure caused by the problem of lower punch movements.
By checking tablet thickness, if any change is observed in the thickness of individual tablets, the machine is stopped, route cause is detected and operation is restored to ensure uniformity of all process parameters of tablets.
To Ensure Uniform Drug Release
As we know, tablet thickness is related to tablet hardness so if tablet thickness is out of range at the lower side it means its hardness is increased and as a result, its disintegration time may be prolonged.
As we discussed earlier due to prolonged disintegration time the dissolution profile will be low and due to variations in tablet thickness, the drug release pattern from individual tablets may not be uniform.
So critical monitoring of tablet thickness is very important during tablet compression operation.
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