International Journal of Pharmaceutics 189 (1999) 91 – 103 Rheological characterization of pharmaceutical powders using tap testing, shear cell and mercury porosimeter E. Guerin a , P. Tchoreloff a , B. Leclerc a , D. Tanguy b , M. Deleuil c , G. Couarraze a, * a Laboratoire de physique pharmaceutique, UMR 8612 du CNRS, Uniersite ´ Paris XI, 5 rue J. B. Cle ´ment, 92296 Cha ˆtenay -Malabry cedex, France b Rhodia, Diision Organique Fine, 24 aenue Jean Jaures, 69153 De ´cines, France c Rho ˆne Poulenc Rorer, De ´ eloppement chimique et pharmaceutique, Sciences Pharmaceutiques, 92165 Antony, France Received 7 January 1999; received in revised form 14 July 1999; accepted 18 July 1999 Abstract Most of the pharmaceutical processes involved in the manufacturing of solid dosage forms are connected with powder flow properties, at least for some of the intermediate steps. Powder flow characteristics are commonly investigated by various measurements, such as, handling angles, tap testing, shear cell measurements, etc. All these approaches allow the calculation of indices characterising powder flowability. Unfortunately, these methodologies are highly product consuming, which is a limitation in the first steps of a novel drug development, when only a small amount of the product is available. The use of mercury porosimetry to evaluate compressibility and flow properties of powders could be a new and alternative approach to obtain insight in the rheological properties of granular medium by the interpretation of the first part of porograms (low pressures). We have developed such an evaluation and compared the results obtained with those given by tap testing and shear cell measurements, applied to four excipients for direct tabletting and three different drugs. Mercury porosimetry turned out to be a sensitive technique, able to provide quantitative information about powder flow properties, complemented by an evaluation of particles micro porosity and size distribution, in a single step. These characterisations are obtained with only 250 mg of bulk powder compared to high quantities ( 100 g) needed for other methods. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Shear cell; Mercury porosimetry; Tap testing; Powder rheology; Compressibility; Flowability indices www.elsevier.com/locate/ijpharm 1. Introduction During a pharmaceutical process, most of the steps such as sieving, pouring, micronizing, mix- ing, pneumatic conveying, grinding, drying, com- paction, are connected with the powders * Corresponding author. Tel.: +33-1-46-83-56-16; fax: + 33-1-46-83-58-82. E-mail address: guy.couarraze@phypha.u-psud.fr (G. Couarraze) 0378-5173/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII:S0378-5173(99)00243-4