Evaluation of tablets

Evaluation of tablets

The compendia, such as the United States Pharmacopeia (USP), and the regulatory bodies, such as the United States Food and Drug Administration (FDA), in addition to historic product-development experience, inform the desired quality attributes of the tablets. Tablets are usually tested for the following characteristics:

Appearance

All tablets should have identical size, shape, thickness, color, and surface markings. The general appearance of the tablet allows monitoring a lot-to-lot and tablet-to-tablet uniformity. Tight control of tablet thickness is required to ensure automated machine operations during its packaging and handling. Tablet-to-tablet thickness within a batch and average thickness of tablets across all batches are defined and controlled.

Uniformity of content

All tablets must be demonstrated to contain the labeled active ingredient and there should be tablet-to-tablet uniformity in drug content. This is usually tested by an analytical method for drug potency (such as high-performance liquid chromatography) in a several individual tablets.

Hardness

Tablet hardness refers to the amount of force required to diametrically crush a tablet. It is representative of the tensile strength of a tablet and is determined by the cohesion characteristics of the powder blend. Tablet hardness impacts tablet disintegration, dissolution, and friability. If tablets are too hard, they may not disintegrate within a reasonable period of time. This can lead to reduced bioavailability and failure to meet the dissolution specification. If they are too soft, then they may not withstand the handling and shipping operations, leading to tablet breakage or chipping (breaking away from edges) and failure during friability testing. Friability is the ten-dency of the tablets to chip or break by tumbling motion.

Friability

Tablet friability represents the tendency of a tablet to shed powder or break into smaller pieces under mechanical stress, such as falling from a fixed dis-tance. It is a function of the fragility of the compressed powder blend, tab-let shape, cohesion, and hardness. Low tablet friability is desired to ensure its physical integrity during packaging, shipment, and handling.

Weight uniformity

Tablets are compressed at a predefined weight. Under the assumption of normality of statistical distribution of tablet weight, all tablets are required to be within a certain range of the predefined tablet weight. Several tablets are weighed individually, and both the average weight and variation of indi-vidual tablet weight from the average are calculated and controlled during the manufacturing to ensure that the tablets contain the desired amounts of drug substances, with no more than acceptable variation among tablets within a batch.

Disintegration

Disintegration of tablets is evaluated to ensure that the tablet dissolves or breaks apart into smaller particles or granules on contact with water under agitation. This allows the DS to dissolve from its primary particles, being fully available for dissolution and absorption from the GI tract. Tablet dis-integration is evaluated in a standardized apparatus that subjects six tablets to a defined mechanical stress in individual reciprocating cylinders in a suitable aqueous medium at 37°C, to reflect the conditions on oral inges-tion. The time it takes for the last of six tablets to disintegrate into smaller particles and disappear from the reciprocating cylinders is called disinte-gration time. The disintegration media required varies depending on the type of tablets to be tested. The disintegration time is generally not more than 15 min for IR tablets.

The disintegration test is used as a control for tablets intended to be admin-istered by mouth, but not for the tablets intended to be chewable and SR.

Dissolution

As drug absorption and physiological availability depend on having the DS in the dissolved state at the site of absorption, dissolution, also termed drug release, is an important property of tablets. The rate and extent of dissolution of a drug are tested in vitro by a suitable dissolution test. Dissolution is used as both a quality control tool to ensure batch-to-batch and tablet-to-tablet uniformity in drug-release characteristics of the tab-lets and sometimes also as a tool for in vitro–in vivo correlation (IVIVC) of drug release (in vitro) and drug absorption (in vivo). Dissolution test provides a means of control in ensuring that a given tablet formulation is similar with respect to the rate and extent of drug release as the batch of tablets were shown initially to be clinically effective.