Hardness and friability are important physical parameters for a tablet. These parameters ensure the strength and structural integrity of a tablet for transportation, packaging and handling before usage.


Hardness

  • The breaking force of tablets is commonly called “hardness” in the pharmaceutical literature; however, the use of this term ismisleading. Tablet breaking force measures the mechanical integrity of tablets, which is the force required to cause them to fail.
  • The test must be run consistently with equipment that has been routinely calibrated. Modern breaking force testers are usually calibrated in kiloponds or newtons. The relationship between these units of force is 1 kilopond (kp) = 1 kilogram-force (kgf) = 9.80 newtons (N).
  • Measurements of breaking force do not take into account the dimensions or shape of the tablet.Tablet orientation and failure should occur in a manner consistent withthe orientation used and failure observedduringthe development of the dosage form.For direct comparisons (i.e., without any normalizations of the data), breaking forcemeasurements should be performed on tablets having the same dimensions,weights,geometry, and consistentorientation in test equipment.
  • Tablet orientation in diametral compression of round tablets without any scoring is unequivocal. That is, the tablet is placedbetweenthe platens so that compression occurs across a diameter. However, tablets with a unique or complex shape may have noobvious orientation for breaking force determination. Interpretation of the breaking force data must consider not only the mean value but the consistency of the test results for multipletablets.

Friability

  • For tablets with a unit weight equal to or less than 650 mg, take a sample of whole tablets corresponding as near as possible to 6.5g. For tablets with a unit weight of more than 650 mg, take a sample of 10 whole tablets.
  • Rotate the drum 100 times, and remove thetablets. Remove any loose dust from the tablets as before, and accurately weigh. If the results are difficult to interpret or if the weight loss is greater than the targeted value, the test should berepeated twice and the mean of the three tests determined.
  • A maximum mean weight loss from the three samples of not more than 1.0% is considered acceptable for most products. Effervescent tablets and chewable tablets may have different specifications as far as friability is concerned. In the case of hygroscopic tablets, an appropriate humidity-controlled environment is required for testing.
  • Use a drum, with an internal diameter between 283 and 291 mm and a depth between 36 and 40 mm of transparent synthetic polymer with polished internal surfaces.The drum is attached to the horizontal axis of a device that rotates at 25 ±1 rpm.
  • The tablets are tumbled at each turn of the drum by a curved projection with an inside radius between 75.5 and 85.5 mm that extends from the middle of the drum to the outer wall.
  • If tablet size or shape causes irregular tumbling, adjust the drum base so that the base forms an angle of about 10° with the horizontal and the tablets no longer bind together when lying next to each other, which prevents them from falling freely.

It is normally appropriate to perform hardness and/or friability testing as an in-process control. Under these circumstances, it is normally not necessary to include these attributes in the specification. If the characteristics of hardness and friability have a critical impact on drug product quality (e.g., chewable tablets), acceptance criteria should be included in the specification.


References:

  • USP NF {1217}
  • USP-NF {1216}
  • ICH Q6A