The Tablet Hardness test is one of the most important in-process tests for tablets which is performed at the start & in between at specified time intervals during the tablet compression operation.
The tablet hardness test is performed after line clearance during in-process testing and we don’t start compression operation until the tablet hardness is not adjusted according to the BMR or batch manufacturing record.
What Is a Tablet Hardness Test?
Tablet hardness test is also known as Crushing Strength Test and is defined as,
- The test , used for tablets by applying pressure or force to check how much force is required to break the tablets.
- In simple words, tablet hardness is defined as follows,
- The breaking force of tablets is known as Tablet Hardness.
History Of Tablet Hardness Test
- The first hardness tester was introduced in 1930 for checking the hardness of tablets.
- In 1950 the strong cobb apparatus was introduced as a tablet tester to check the hardness of tablets in pharmaceutical industries.
- The patent for the Strong Cobb Tester was gained by Albrecht in 1953.
Apparatus Used To Check Tablet Hardness
With time, various types of tablet testers were introduced for checking the hardness of tablets and some are given as follows,
- Monsanto Hardness Tester
- Strong Cobb Hardness Tester
- Pfizer Hardness Tester
- Erweka Hardness Tester
- Dr Scheluenger Pharmatron Hardness Tester
- Kraemer Elektronik’s Hardness Tester
Unit Of Hardness Of Tablet
As we know, all measurements have some specific units and the same is the case for tablet hardness. The tablet hardness is a force, so tablet hardness is measured in the following units,
- Kilograms (kg)
- Newton (N)
- Pound (lb)
- Kilopound (kp)
- Strong Cobb (SC)
How To Adjust Tablet Hardness?
- Tablet Hardness adjustment is a technical job and skilled compression machine operators adjust it according to the requirements mentioned in the BMR.
- After line clearance for compression operation, the powder is filled in the hoppers of the compression machine and the weight of the tablet is adjusted.
- After weight adjustment, the knob for pressure application is rotated to increase the pressure which is exerted by the compression rollers and transmitted by punches to the powder or granules which are previously filled in the dies.
Precautions For Tablet Hardness Adjustment
- We do not apply too much load or pressure at the start because it may result in tooling damage due to extra pressure.
- Always adjust weight first by applying little pressure to form a soft tablet.
- When the required weight is achieved then again apply more pressure to bring it in range.
- Again check the weight and take a sample for hardness checking in the Inprocess lab using a hardness tester.
- If hardness is within range, we start a compression operation.
Tablet Hardness Test Is Official Or Non-Official Test
In-process tests for tablets are divided into two categories one is the official test and the other is the non-official test. As for as tablet hardness test is concerned it comes under the category of Non-Official test.
How To Check Tablet Hardness?
Nowadays sophisticated hardness testers are available in pharmaceutical industries to determine or check the tablet hardness.
Parts of Hardness Tester
The hardness tester has the following main parts,
- Electric Driven Jaw
- Static Base Plate
- Stationary Support
- Rejection Holder
Electric Driven Jaw
- An electrically driven jaw /rod is the main component of a tablet hardness tester and its role is to apply force or load to the tablets.
Static Base Plate
- The static base plate is the SS base plate attached to the main body of a hardness tester. The electrically driven jaw moves over this static base plate.
- Stationary support is attached to the end of the static base plate. It provides support against which the tablet is crushed when the load is applied through the moving jaw.
- It covers the base plate and moving jaw and prevents the spread of broken tablet pieces.
- A rejection holder is placed below the stationary plate to collect the waste and broken tablets.
A display screen or HMI is the main portion of the tablet hardness tester from which various operations are controlled like,
- Movement Of Jaw
- Select Number Of Tablet
- A printer may also be attached with a hardness tester to get prints of hardness values.
Procedure To Check Tablet Hardness
The tablet is placed on a static base plate along with stationary support.
Enter the number of tablets from HMI for which you want to run a hardness test.
Press the start button, the movable or electrically driven jaw will move towards the stationary support.
It applies force over the tablet and breaks or crushes it.
The value of force is displayed over HMI and in the same way we find out the hardness of all selected tablets.
In the end, take a printout of the values and attach it to the BMR.
If the hardness value is within range, proceed with the compression operation and if not in range, adjustments are made and again repeat the process.
Factors Affecting Tablet Hardness
Following are some key factors which may affect tablet hardness,
- Amount Of Binder
- Moisture Content
- Compression Force
Amount Of Binder
- Tablet hardness is dependent on the nature of powders or granules, if our granule’s quality is good our hardness will also be good and vice versa.
- Binders are used to convert powders into granules and to give strength to granules.
- Less amount of binder results in fragile granules and results in low hardness and a higher quantity of binder may result in too hard granules, high hardness and may retard drug release, so an optimum quantity of binders is used.
- Microcrystalline cellulose or Avicel is known as a dry binder and it is used extragranular to give strength to tablets and to increase tablet hardness without affecting drug release.
- The optimum level of moisture content is retained in granules during the drying stage of wet granulation because it creates strong bounding during compression operation & provides us with good tablet hardness
- Force or load applied during compression operation is directly proportional to the tablet’s hardness.
Effect Of Hardness On Tablet Properties
The hardness of tablets usually affects the following,
- The disintegration time of tablets is greatly affected by the hardness of the tablets.
- If tablet hardness is high, the tablet will be more strong and it will take more time to disintegrate and vice versa so hardness is adjusted in such a way to get the required disintegration time as specified in the monograph.
- Dissolution is one of the most important in-process tests of tablet compression operation and is inversely related to tablet hardness.
- If tablet hardness is high, disintegration time will be prolonged and drug release will be delayed so dissolution will be low and vice versa.
Purpose Of Tablet Hardness Test
A common question may arise in mind, why do we perform a tablet hardness test?
The answer is as follows,
- A tablet hardness test is performed to check the strength of tablets means to know if the tablet hardness is within range or not as mentioned in BMR.
- One common reason to check tablet hardness is to adjust the compression force to start compression operation.
- Tablet hardness is checked to ensure that disintegration time is within range.
- Tablet hardness is checked to ensure that the dissolution profile will be according to specifications.
- A tablet hardness test is performed to ensure that tablets are strong enough to remain intact during following operations
- Tablet Coating Operation
- Tablet Blistering Operation
- Tablet Packaging Operation
If tablet hardness is not of the required level it may result in breakage or surface damage of tablets during the above-mentioned operations.
- Disintegration Test
- Difference between disintegration & dissolution.
- Types and Mechanism of Tablet Disintegrants.
- How To Perform Friability Test?
- Weight Variation Test
- Stages and Mechanism of Tablet Compression.
- Advancements in tablet compression machines.