SELECTION OF SUSPENDING AGENTS 133 be sure that the desired properties are still present. If, for instance, upon the addition of sucrose to a suspension vehicle, there is a decrease in yield stress, more suspending agent should be added to make up for the loss. If, on the other hand, an increase in viscosity is shown when sucrose is added, the suspension may be formulated as such as long as the yield stress remains unaffected and the product is not too thick. In general, the rheological behavior of the suspension should be checked at the various stages of formulation, particularly after the addition of each ingredient. If there is no significant change in rheological behavior, or if the rheological properties of the suspension can be restored to their original state without further change, this is an indication that the suspension may have good shelf-life stability. (Received September 20, 1962) REFEP. ENCES (1) T. Higuchi, y. •/m. Pharm./lssoc., $ci. Ed., 47, 657 (1958). (2) R.J. Meyer and L. Cohen, J. Soc. Cos•tET•C C•qEms'rs, 10, 143 (1959). (3) J. C. Samyn, •. Pharm $ci., 50, 517 (1961). (4) E. C. Foernzler, A. N. Martin and G. S. Banker, •. •/m. Ph•rm. •lssoc., $ci. Ed., 49, 249 (1960). (5) C.W. Chong, S. P. Eriksen, and J. V. Swintosky, presented at December, 1962, meeting ooe A.A.A.S.

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