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M Tablets & Capsules March 2015 25 inspection When to use dimensional tablet sorters Fred A. Rowley Solid Dosage Training and Troubleshooting Dimensional sorters are useful for removing off-weight tablets, but they should only be used as defined by an SOP, not as a means of quality assurance. y first encounter with overweight (superpotent) tablets was in 1994, when a manufacturer sought my help after the FDA found some in a retained sample. Since that time, I've encountered over- and underweight (sub- potent) tablets many times, none of which left the plant. But in early 2008, nearly 100 recalls stemming from off- weight tablets were reported in North America, and four companies reported "near misses" [1-5]. As a result, some manufacturers have opted to use dimensional sorters to identity off-weight tablets. Is that acceptable practice? It depends. Weight matters Weight defects originate on the tablet press. They do not indicate a formulation problem, since the same for- mulation usually results in on-spec tablets. Overweight tablets—far more common than underweight tablets— can pose a danger to patients because they contain too much active pharmaceutical ingredient (API). And most overweight tablets are between 130 percent and 210 per- cent of the target weight. Underweight tablets vary more narrowly, but regardless of whether the tablets have too much or too little API, the risk to patients can be serious, as noted in an FDA warning letter that also cited the company's use of a dimensional sorter [6]: Your Quality Assurance "Hold" documents for the lots noted that lots were sorted in a thickness sorter in an effort to eliminate aberrant tablets as a corrective action. However, your firm did not document the num- ber of aberrant tablets that were rejected during sorting or any examination of other batches that may have been impacted. In addition, your firm did not evaluate the state of control of the process, including whether A multi-lane roll sorter it is capable of consistently producing tablets meeting specifications. Digoxin tablets have a narrow therapeu- tic range and over or underweight tablets can have a significant effect on the patient's health. Dimensional sorting A gravimetric method (checkweighing) is the most accurate means of determining tablet weight, but many manufacturers opt for dimensional sorting, also called thickness sorting, because tablet checkweighers are slow and relatively expensive. Dimensional sorting—a tech- nology used in many industries to separate parts by size difference—was first used in the pharmaceutical industry to eliminate foreign tablets (those with a different size or shape). Now the primary pharmaceutical application is separating underweight (thin) tablets and overweight (thick) tablets from those of the right size (on-spec), examples of which are shown above. The machines use either rollers that form channels (photo) or a rotating disc with machined slots.

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