Tablets & Capsules

TC0317

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42 March 2017 Tablets & Capsules volume of the compact. The compact is then transferred to a built-in balance to measure its mass. The ratio of the envelope density to the pore-free density (typically deter- mined by a pycnometer) yields the SF of the compact. (3) How laser-based SF measurement works To determine the envelope volume, two laser distance sensors whose beams face each other measure the dis- tance to the lower and upper surfaces of the compact. Because the fixed distance between the two lasers is known, the thickness at the point (x,y) on the ribbon or tablet where the beams would intersect can be calculated using Equation 4: T (x,y) = D - U (x,y) - L (x,y) (4) where T(x,y) is the thickness of the compact at point x,y, D is the distance between the two lasers, U(x,y) is the distance from the upper laser to the upper surface of the compact at x,y, and L(x,y) is the distance from the lower laser to the lower surface of the compact at x,y. By moving the ribbon between the stationary lasers in a scanning pattern, thickness data are acquired at many (x,y) positions and the data are used to calculate the envelope volume. Knowing that value and the compact's mass enables you to calculate the SF. Working under computer control, a laser-based SF measurement system can perform a series of scans in the x direction, with the y distance between each scan selected by the user. A typi- cal y value is 700 microns, while the typical x distance between data points is approximately 10 microns. The measurement takes approximately 2 minutes. Iyer et al. [3,4] describe an early, noncommercial ver- sion of a laser-based system. Allesø, who used an early commercial version, reports excellent agreement between laser-based measurements and those obtained by the oil- intrusion method when making "back-to-back" measure- ments on the same samples. Unlike the oil-intrusion method, however, the laser-based approach is fast and nondestructive. The most recent commercial version of the laser-based system has an option that allows multiple ribbons or multiple tablets to be pre-loaded so you can take unattended measurements of multiple samples. The advantages of using laser distance sensors to mea- sure the volume of compacts include the ability to assess fragile and relatively small ribbon fragments, no special sample preparation, minimal operator training, and results that are independent of both operator experience and the specific instrument taking the measurement. Applying SF measurement to production challenges Determining roller compactor settings for different production rates. Once the optimal SF of a formulation is determined—one that provides adequate flowability and suitable re-compactability—it is important that it be maintained. That requires correctly setting the roller com- pactor's force, roller gap, roll speed, etc. for the initial pro- duction requirements, and then adjusting those parame- ters as needed as production is scaled up. Unfortunately, knowing what force is required to produce ribbons of a certain SF at one roller gap doesn't enable you to predict the force required to produce the same SF at the new (wider) gap required to accommodate a production increase. But taking SF measurements using a laser is fast, so you can address this problem by iteratively adjusting the roller compactor's settings after changing the roller gap until the thicker compacts have the same SF as the original ribbons. Adjusting settings when changing roller compactor models. When a formulation is developed at one facility and produced at another, the make and/or model of the equipment will likely differ. The challenge is to quickly determine the compactor settings that will preserve the SF as formulated. Although Allesø showed that it is possible to use the same settings on two models of a single manufacturer's roller compactors and obtain the same SF, that may not always be the case. Thus, when production is moved to a different roller compactor, it can require substantial effort to determine what settings on the new compactor will yield the same SF. This is because the traditional techniques of Envelope density Pore-free density SF = An SF measurement system uses two opposed laser beams (simu- lated for illustration) to scan a compacted ribbon and a tablet. In the foreground are multiple ribbon pedestals and multiple tablet "nests" that allow unattended measurement.

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