OIL-IN-WATER CREAM STABILITY 229 DSC and VTXRD thermal analysis methods were used to characterize and classify multi-sourced grades of glyceryl monostearate. These accurately predicted the effects that each lot of glyceryl monostearate would have on the consistency and bleed propen- sity of the finished cream. Cone penetrometer and wire-mesh screen testing were utilized for assessing consistency and bleed potential of the bulk cream immediately after manufacture and during bulk cream storage prior to approval for packaging. Based on this study, in order to overcome variable consistency and bleed problems, the following recommendations can be made: 1. If possible, use only glyceryl monostearate with higher acid value (5-15) and op- timal thermal analysis VTXRD pattern. 2. Cream batches prepared using glyceryl monostearate with low acid value (below 5) should be stored at 20ø-33øC until a firm consistency develops and no bleed is evident when tested by the wire-mesh screen method. REFERENCES (1) G. L. Flynn, "Unique Physicochemical Systems Used Topically," in Modern Pharmaceutics, G. S. Banker and C. T. Rhodes, Eds. (Marcel Dekker, New York and Basel, 1979), Vol. 7, pp. 298-309. (2) H. Schott, "Rheology: Self-Bodying Action of Mixed Emulsifiers," in Remington's Pharmaceutical Sciences, 17th ed., A. J. Gennaro, Ed. (Mack Publishing Company, Easton, Pennsylvania, 1985), pp. 341-342. (3) R. G. Harry, "Polyhydric Alcohol Esters of Fatty Acids," in The Principles And Practice of Modern Cosmetics, W. W. Myddleton, Ed. (Chemical Publishing Company, New York, 1963), pp. 357-367. (4) "Glyceryl Monostearate," in Handbook of Pharmaceutical Excipients (American Pharmaceutical Associa- tion, 1986), pp. 125-126. (5) R. M. Cornish, Studies ofglyceryl monostearate, J. Soc. Cosmet. Chem., 19, 109-117 (1968). (6) N.H. Kuhrt, R. A. Broxholm, and W. P. Blum, Conjoined crystals. 1. Composition and physical properties,J. Am. Oil Chemists Soc., 4, 725-733 (1963).
j. Soc. Cosmet. Chem., 40, 231-242 (July/August 1989) The effect of solvents on solute penetration through fuzzy rat skin in vitro JOHN N. TWIST AND JOEL L. ZATZ, Rutgers University College of Pharmacy, P.O. Box 789, Piscataway, NJ 08854. Received December 19, 1988. Synopsis Solvents common to cosmetic and pharmaceutical formulations, including water, dimethylisosorbide, three aliphatic alcohols, and three polyols, were studied using theophylline and methylparaben as model per- meants. The integrity of fuzzy rat skin was maintained for about two days when fully hydrated and only one day when exposed to methanol. The maximal permeation rate of each solute was markedly dependent on the solvent, indicating that solvent/skin interactions contributed significantly to permeation. Flux ratios for the solvents relative to water were computed for each permeant. A perfect rank order correlation between permeants was observed. Among the alcohols, methanol was most effective in enhancing flux of both compounds, followed by ethanol and then 1-propanol. Propylene glycol had a small negative effect, while the more polar polyols markedly reduced the flux ratio. Flux-concentration profiles for methylpar- aben and flux differences between the alcohols suggest that the interaction mechanism differs from that with polydimethylsiloxane membranes. INTRODUCTION In addition to industrial toxicologic considerations, the permeability characteristics of skin are of paramount importance in the development of pharmaceuticals and cos- metics. Topically applied drug entities may be used to achieve either local or systemic pharmacologic actions (1). Often, to avoid allergic or toxic reactions, it is desirable to prevent or limit the penetration of materials that have been applied to the skin. Cos- metic preparations should be formulated to reduce penetration of components that are irritating or can induce allergic responses. Contact with solvents can markedly alter the physical-chemical properties, including permeability, of membranes. Solvent interaction may alter membrane resistance by affecting solute mobility and/or capacity of the membrane to contain solute. In order to quantirate interactive effects it is necessary to account for any changes in solute release from the vehicle. Suspensions should yield equivalent solute flux in the absence of solvent-induced membrane damage. The literature on solvent effects on skin perme- John N. Twist's current address is E. R. Squibb and Sons, 1 Squibb Drive, New Brunswick, NJ 08903. 231
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