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drawn about the tabletting properties of a formulation. Fortunately, the impact of flashing on tabletting data can be minimized or even eliminated by a simple yet effective method: polishing the tablet using fine sandpa- per (figures 1c and 1d) [1]. Expedited tablet friability test Tablet friability is defined by the percentage of weight loss under controlled conditions when tablets are dropped from a fixed height a predefined number of times, usually 100, using a friabilator. It is an excellent performance test of a tablet's mechanical strength. High friability usually indicates problems associated with excessive loss of material, including the active pharma- ceutical ingredient (API), when tablets are coated or handled. Traditionally, a batch of tablets is loaded into a friabi- lator and the average weight loss of a whole set of tablets is used to calculate friability. In most cases, the tablet's mechanical properties may be deemed satisfactory if fri- ability is less than 1 percent. (Some researchers use a more conservative criterion, less than 0.8 percent weight loss.) Although this test provides very useful information about the quality of a batch of tablets, it has limited value in guiding formulation design and process development. In an early development stage, the manufacture of large tablet batches for friability testing is usually not possible due to the limited availability of the API. We thus developed an expedited friability test based on the assumption that stresses experienced by individual tablets and their weight loss kinetics are representative of a batch of identical tablets [2]. This assumption was vali- dated using both plastic and brittle tablet excipients. See Figure 2. The test uses the same existing friabilator, but instead of using a set of identical tablets, it uses tablets prepared under different conditions (e.g., pressure, shape, weight, etc.). By quantifying the weight loss of individual tablets, we generated friability data as a function of the tablet properties (e.g., size and weight) or processing conditions (speed and pressure) from each run. With the expedited friability test, useful information can be quickly generated to guide tablet product devel- opment using only a small amount of API. It also enables formulators to make data-based decisions about tooling, formulation optimization, and process design within a short period. Industry-wide adoption of this test method would significantly improve efficiency and quality during development of tablet products. A new method to quantify tablet brittleness During manufacture and handling, brittle tablets are more susceptible to chipping, lamination, and problems associated with high friability. Very plastic materials, on the other hand, tend to have other problems, such as over-granulation during wet granulation and the loss of tabletability after dry granulation [3]. Usually, a good tablet formulation balances brittleness and plasticity. Thus, a plastic API should be formulated with a more brittle excipient matrix, while a brittle API should be for- mulated with a more plastic excipient matrix. The ratio- nal selection of excipients for a given API requires know- ing the brittleness and plasticity of the API and the intended excipients. Recent research allows brittleness to be quantified using a new tablet brittleness index (TBI). The TBI is essentially the reciprocal of the elastic strain a tablet can sustain before plastic deformation or brittle fracture 32 May 2017 Tablets & Capsules Figure 3 TBI values of some common tablet excipients and blends [4] Figure 4 Tablet hardness of three grades of MCC, as mea- sured by the macro-indentation method [8] Reproduced with permission Reproduced with permission LM = lactose monohydrate MCC = microcrystalline cellulose DCPD = dibasic calcium phosphate dihydrate Note: The hardness profiles are superimposable despite the different particle sizes. Hardness extrapolated to zero porosity may be used to quantify the plasticity of the material. 1000 100 10 1 Porosity Hardness (MPa) 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 400 350 300 250 200 150 100 50 Pressure (MPa) TBI 0 30 60 90 120 150 200 Avicel PH 105 Avicel PH 102 Avicel PH 200 MCC LM DCPD LM:MCC=1:3 LM:MCC=1:1 LM:MCC=3:1 A more reliable, direct method of assessing plasticity is to measure indentation hardness.