Tablets Evaluation, Shape of Tablets, Thickness of Tablets, Tablets Appearance, Weight Uniformity, Medicaments Uniformity, Tablet Hardness, Tablets Friability, Tablets Disintegration, Tablets Dissolution.

Evaluation of tablets:

Evaluation of tablets is part of the quality control of tablets. It helps to comply with pharmacopeia requirements. The following evaluation test is carried out after the manufacturing of tablets.

1. Shape of tablets:

Pharmacopoeia states tablets are disc-shaped with flat or convex surfaces. However, tablets in other shapes are also available.

2. Thickness of tablets:

Tablet thickness is measured by using micrometer calipers. There should be uniformity in thickness. ±5% variation is allowed in tablet thickness. Tablet thickness variation is mainly due to differences in the densities of granules, the variation in the force applied by the machine during tablet compression, or the variation in the speed of the machine to compress tablets.

3. Tablets appearance:

Tablets are examined under a lens there should be uniform texture on the tablet surface.

4. Weight uniformity:

All tablets of a single batch should have uniform weight. Some variation in tablet weight is allowed.

• IP Limits

  • Weight of tablets: Less than 85 mg.  Weight variation allowed: ±10%.

  • Weight of tablets: Less than 85 mg to 250 mg. Weight variation allowed: ±7.5%.

  • Weight of tablets: More than 250 mg. Weight variation allowed: ±5%.

• USP Limit

  • Weight of tablets: Less than 130 mg, Weight variation allowed: ±10%.

  • Weight of tablets: Less than 130 mg to 324 mg, Weight variation allowed: ± 7.5%.

  • Weight of tablets: More than 324 mg. Weight variation allowed: ±5%.

Weigh 20 tablets. Calculate the average weight of individual tablets. Weigh each tablet individually. Not more than two tablets should be above the weight variation range if 10 tablets are used to calculate weight variations. Then not more than 1 tablet should be above the weight variation range. Weight variation test is carried out during the manufacturing process at regular intervals.

Weight variation shall cause variation in dose.

5. Medicament uniformity:

Active pharmaceutical ingredients in tablets should be uniform in each tablet. 20 tablets or as mentioned in dosage form of medicaments are used to calculate content uniformity in tablets. Content in the tablet is calculated by assay of medicaments as mentioned in the pharmacopeia monograph of that tablet.

6. Tablet hardness:

The mechanical strength of tablets decides the hardness of tablets. Pharmacopoeia does not mention evaluating tablets on the basis of their hardness. The hardness of tablets plays a crucial role during transportation, dispensing, and disintegration of tablets after administration. There are two apparatuses to find out the hardness of tablets.

• a. Monsanto hardness tester: It consists of a metallic cylinder that has a scale and indicator to measure pressure applied on tablets. Scale gives a reading of pressure on a tablet in kg or pounds. There is a spring inside The metallic cylinder. One end of the cylinder has a rotating knob to apply pressure on the spring. The other end of the cylinder has a spindle-shaped moving jaw. And a fixed spindle-shaped jaw. It holds the tablet in between both jaws.

Fix the indicator level of the metallic cylinder at zero scale by using the rotating knob. Fix the tablet vertically in between both jaws. Apply pressure on the spring by rotating the knob. This will apply pressure on the tablet. Keep the knob rotating till the tablet breaks into fragments. Not down the level of indicator on the scale. This will be the hardness of the tablet. The hardness of tablets should be around 5 kg.

• b. Pfizer tablet hardness tester: It works on the principle of plier. It has a pressure dial to give a reading of pressure applied on a tablet. Place the tablet vertically in between two jaws. Press the handle to apply pressure on the jaws and tablet. Apply pressure till the tablet breaks. Reading on the pressure dial indicates the hardness of tablets.

7. Friability:

Compressed tablets withstand wear and tear during their transportation and dispensing. However, there may be a loss of solid particles as a powder from the surface of tablets. It is checked by the friability test apparatus. Pharmacopoeia does not recommend this test. But manufacturers check the friability of tablets. Friability in tablets develops an unpleasant appearance in tablet along with loss of ingredients during transportation and dispensing. The friability test apparatus consists of disc shaped plastic chamber. It has a partition from its center to the periphery that divides the chamber into two parts. It has a motor that revolves plastic chamber at 25 r.p.m. Weigh 20 tablets and place them inside a plastic chamber. Revolve the plastic chamber for four minutes or 100 revolutions. In each revolution, tablets will fall from a height of 6 inches. Weigh all tablets after 100 revolutions. Loss of weight should not be more than 0.8%.

8. Tablets disintegration:

Break down of tablets into smaller pieces after swallowing is called disintegration. The time required to break down a tablet into smaller pieces is called disintegration time. Disintegration of tablets affects the dissolution of medicaments and their absorption from GIT. The rate of disintegration depends upon the type of compressed tablets. For example, chewable tablets and lozenges do not require disintegration. The disintegration time of tablets may be as short as 1 minute and as long as 30 minutes. The disintegration time of the tablet is evaluated by using the disintegration test apparatus. The Test is performed as prescribed in the pharmacopeia.

Tablet disintegration apparatus:

It is used to test the breakdown of the intact tablets into smaller particles inside the liquid medium. Indian pharmacopeia provides specifications for apparatus and guidelines to test tablet disintegration.

The apparatus consists of the following parts

• i. Basket rack assembly: It holds six transparent glass tubes open at both ends. The lower end has wire mesh made of stainless steel wire and one plastic stopper. The diameter of the stopper is 20.7 mm and the thickness is 9.5 mm. The stopper does not allow tablets to come out from the upper end of the glass tube during the disintegration test. The diameter of the wire is 0.3 mm and the aperture size of the wire mesh is 1 mm. The apparatus has an electric motor to move the basket rack assembly up and down vertically. Its movement speed is 30 cycles per minute. In each cycle, it travels 55mm to 65mm.

• ii. Beaker: 1000 ml capacity beaker to hold disintegration medium. The basket rack assembly moves up and down inside this liquid. At the highest point wire mesh of the glass tube should be at least 25 mm below the surface of the liquid. At the lowest point wire mesh of the glass tube should be 25 mm above the bottom of the beaker.

• iii. Thermostatically controlled water bath: It holds water or any suitable medium for tablet disintegration as specified in the monograph of the tablet under test. The water bath maintains the temperature of the disintegrating medium at 37 degrees C ± 20 C throughout the disintegration test procedure.

• iv. Timer: The apparatus has also a timer that sets the duration of testing.

Working:

For uncoated tablets: Place distilled water in a beaker or dissolution media as mentioned in the monograph of the tablet. Place water in a water bath of disintegration test apparatus. Place one tablet in each glass tube and ad put the disk in each glass tube to cover the tablets. The disk does not allow tablets to float and comes out from a glass tube. Switch on the disintegration test apparatus to maintain the water bath temperature at 37 degrees C ±2OC. Switch on the up-and-down movement of the glass tube inside the beaker. Assure at the highest point, the wire mesh of the glass tube should be at least 25 mm below the upper surface of the liquid. At the lowest point, the wire mesh of the glass tube should be 25 mm above the bottom of the beaker.

Operate the disintegration test apparatus for 15 minutes or as stated in the monograph. If one or two tablets disintegration failed to comply pharmacopoeia requirement then repeat the test for an additional 12 tablets. 16 out of 18 tablets should pass the disintegration test.

For coated tablets: Operate the disintegration test apparatus for 60 minutes or as mentioned in the monograph. Use 0.1N Hcl in place of distilled water in a beaker. If all six tablets do not disintegrate repeat the test with the other 12 tablets. Not less than 16 tablets should pass the test.

For enteric-coated tablets: Operate the disintegration test apparatus for 120 minutes or as mentioned in the monograph. Use 0.1N Hcl in place of distilled water in a beaker. Do not use a disc in a glass tube. No tablet should disintegrate or crack.

Use mixed phosphate buffer pH 6.8 in place of 0.1N Hcl in a beaker. Operate the disintegration test apparatus for 60 minutes or as mentioned in the monograph. If all six tablets do not disintegrate repeat the test with the other 12 tablets. Not less than 16 tablets should pass the test.

9. Tablets dissolution:

API of tablets must be in solution inside GIT to be absorbed into the blood. Thus dissolution test is carried out to find out the time required to dissolve API in vitro. A dissolution test is carried out to measure the rate of drug release from tablets. Type II Dissolution test apparatus as mentioned in USP and IP is the most commonly used dissolution test apparatus.

Types of dissolution test apparatus USP:

• · Type I: Rotating basket type apparatus I,

• · Type II: Paddle type apparatus II,

• · Type III: Reciprocating cylinder type apparatus III,

• · Type IV: Flow-through cell type apparatus IV,

• · Type V: Paddle over disk type apparatus V,

• · Type VI: Cylinder type apparatus VI,

• · Type VII: Reciprocating disk type apparatus VII,

Types of dissolution test apparatus IP:

• · Type I: Paddle type apparatus I,

• · Type II: Basket type apparatus II,

Types of dissolution test apparatus BP:

• · Type I: Basket Type apparatus I,

• · Type II: Paddle Type apparatus II,

• · Type III: Flow-through cell type apparatus III.

Type I: Rotating basket dissolution test apparatus: It consists of a thermostatically controlled water bath that holds beakers made of borosilicate glass. Beakers have semi-hemispherical bottoms and a capacity of 1000 ml. Each beaker has a stainless steel shaft holding a cylindrical basket at its end. The apparatus has a motor to rotate the shaft and cylindrical basket at its vertical axis. The speed of rotation can be controlled as per requirement. The most common speed is 100rpm. It is normally preferred for tablets that float and disintegrate

Type II Paddle dissolution test apparatus: It consists of a thermostatically controlled water bath that holds a dissolving flask made of borosilicate glass. Beakers have semi-hemispherical bottoms and a capacity of 1000 ml. Each beaker has a stainless steel vertical shaft holding a paddle at its end. Paddles are specially coated to resist the disturbance due to stirring. The paddles and shaft are connected to a motor. The motor rotates at a fixed speed. The Tablets are placed in a dissolving flask with a circular bottom to reduce the turbulence of the dissolution medium. Its operating motor speed is usually at 40 rpm and the operating temperature is 37oC ±2oC.

Alok Bains