QUALITY CONTROL TESTS FOR TABLETS
According to WHO, term quality control refers to the sum of all procedures undertaken to ensure the identity and purity of a particular pharmaceutical. Quality control is an essential operation of the pharmaceutical industry.
Drugs must be marketed as safe and therapeutically active formulations whose performance is consistent and predictable. It not only protects the manufacturer against compensation claims, but also guarantees the patient a safe and effective product. QC measurements include stability testing of the drug formulation, dissolution testing and analysis of raw materials and synthesis products majorly.
Quality Control Tests for Tablets
The quality control tests performed for tablets include-
- Organoleptic Properties
- Thickness and diameter
- Weight variation
- Drug content
- Disintegration time
- In-Vitro dissolution
a. Organoleptic Properties
Color is a vital means of identification for many pharmaceutical tablets and is also usually important for consumer acceptance. The color of the product must be uniform within a single tablet, from tablet to tablet and from lot to lot. Non uniformity of colouring not only lack esthetic appeal but could be associated by the consumer with non-uniformity of content and general poor product quality. Non uniformity of colouring is usually referred to as mottling. Color distribution must be uniform with no mottling. For visual color comparison compare the color of sample against standard color.
b. Thickness and diameter
Tablet thickness is determined by the diameter of the die, the amount of fill permitted to enter the die cavity, the compaction characteristics of the fill material, and the force or pressure applied during compression. To manufacture tablets of uniform thickness during and between batch productions for the same formulation, care must be exercised to employ the same factors of fill, die, and pressure. The degree of pressure affects not only thickness but also hardness of the tablet; hardness is perhaps the more important criterion since it can affect disintegration and dissolution. Thus, for tablets of uniform thickness and hardness, it is doubly important to control pressure. Tablet thickness also becomes an important characteristic in packing operations and in counting of tablets using filling equipment which uses the uniform thickness of the tablets as a counting mechanism.
Tablet weight is mainly affected by factors such as tooling of the compression machine, head pressure, machine speed and flow properties of the powder. Inconsistent powder or granulate density and particle size distribution are common sources of weight variation during compression. Variation between tablet with respect to dose and weight must be reduced to a minimum. Uniformity of weight is an in process test parameter which ensures consistency of dosage units during compression. Take 20 tablets and weighed individually. Calculate average weight and compare the individual tablet weight to the average. The tablet pass the U.S.P. test if no more than 2 tablets are outside the percentage limit and if no tablet differs by more than 2 times the percentage limit.
Hardness of Tablets Hardness may be defined as the resistance of tablets to capping, abrasion or breakage under conditions of storage, transportation and handling. Tablet hardness has been associated with other tablet properties such as density and porosity. Hardness generally increases with normal storage of tablets and depends on the shape, chemical properties, binding agent and pressure applied during compression. It is non-official quality control method. It is not prescribed by I.P. Hardness test: The small and portable hardness tester was manufactured and introduced by Monsanto in the Mid1930s. It is now designated as either the Monsanto or Stokes hardness tester. The instrument measures the force required to break the tablet when the force generated by a coil spring is applied diametrically to the tablet. Hardness generally measures the tablet crushing strength. Various devices used to test hardness are: Monsanto tester, Pfizer tester, Strong-cobb tester and schleuniger tester, erweka tester.
It is may be defined as the excessive breakness of tablets during mechanical shocks of handling in manufacture, packaging, and shipping. Friction and shock are the forces that most often cause tablets to chip, break. In friability test the tablets are prone to abrasion hence enabling us to check for the tablet strength under application of force in different manner. Friability of a tablet can determine in laboratory by Roche friabilator. This consist of a plastic chamber that revolves at 25 rpm, dropping the tablets through a Distance of six inches in the friabilator, which is then operate for 100 revolutions. The tablets are reweighed. Compress tablet that lose less than 0.1 to 0.5 % of the Tablet weigh are consider acceptable.
f. Drug content
The content uniformity test is used to ensure that every tablet contains the amount of drug substance intended with little variation among tablets within a batch. Randomly select 30 tablets. 10 of these assayed individually. The Tablet pass the test if 9 of the 10 tablets must contain not less than 85% and not more than 115% of the labelled drug content and the 10th tablet may not contain less than 75% and more than 125% of the labelled content. If these conditions are not met, remaining 20 tablets assayed individually and none may fall outside of the 85 to 115% range.
g. Disintegration time
For a drug to be absorbed from a solid dosage form after oral administration, it must first be in solution, and the first important step toward this condition is usually the break-up of the tablet; a process known as disintegration. The time of disintegration is a measure of the quality. The U.S.P. device to test disintegration uses 6 glass tubes that are 3” long; open at the top and 10 mesh screens at the bottom end. To test for disintegration time, one tablet is placed in each tube and the basket rack is positioned in a 1-L beaker of water, simulated gastric fluid or simulated intestinal fluid at 37 ± 20 C such that the tablet remain 2.5 cm below the surface of liquid on their upward movement and not closer than 2.5 cm from the bottom of the beaker in their downward movement. Move the basket containing the tablets up and down through a distance of 5-6 cm at a frequency of 28 to 32 cycles per minute. Floating of the tablets can be prevented by placing perforated plastic discs on each tablet. According to the test the tablet must disintegrate and all particles must pass through the 10 mesh screen in the time specified. If any residue remains, it must have a soft mass.
Dissolution is the process by which a solid solute enters a solution. Dissolution is pharmaceutically defined as the rate of mass transfer from a drug substance into the dissolution medium or solvent under standardized conditions of liquid/solid interface, temperature and solvent composition. It is a dynamic property that changes with time and explains the process by which a homogenous mixture of a solid or a liquid can be obtained in a solvent. It happens to chemically occur by the crystal break down into individual ions, atoms or molecules and their transport into the solvent. Dissolution is considered one of the most important quality control tests performed on pharmaceutical dosage forms and is now developing into a tool for predicting bioavailability, and in some cases, replacing clinical studies to determine bioequivalence. Two types of apparatus are generally used to carry out dissolution.