COMPATIBILITY STUDIES IN BINARY MIXTURES OF AVOBENZONE 325 Figure 4. DSC scan of avobenzone with cetearyl alcohol/sodium lauryl sulfate/sodium cetearyl sulfate. Table III Results of Analysis of IST Samples After 15 Days of Storage at Stressed Conditions Samples Ratio drug–excipient (1:1) % Remaining Avobenzone 101.5 Avobenzone + cetearyl alcohol/sodium lauryl sulfate/sodium cetearyl sulfate 98.8 Avobenzone + cetearyl alcohol/ceteareth 20 98.7 Avobenzone + isopropyl myristate 95.6 Avobenzone + glycerin 91.3 Avobenzone + BHT 103.3 Avobenzone + diethylhexyl syringylidene malonate 98.0 Avobenzone + cetearyl alcohol 97.7 Avobenzone + caprylic capric triglyceride 92.1 Avobenzone + paraffi num liquidum 93.4 Avobenzone + propylparaben 94.7 CONCLUSIONS The compatibility and stability of avobenzone with different excipients was studied by DSC, IST, and FT-IR spectroscopy. The results confi rmed that DSC supported by IST/ HPLC and FT-IR could be used collectively to study compatibility of drug–excipient mixtures. The DSC technique offers signifi cant advantages, therefore it is considered as a fast screening tool for drug–excipient interaction in a preformulation process. No evi- dence of interaction was observed between avobenzone and the majority of excipients

JOURNAL OF COSMETIC SCIENCE 326 used in the development of cosmetic formulations. However, based on the DSC results alone, an interaction was suspected between avobenzone and few of the excipients cetearyl alcohol, isopropyl myristate, propylparaben, diethylhexyl syringylidene malonate, ca- prylic capric triglyceride, BHT, glycerin, cetearyl alcohol/ceteareth 20, cetearyl alcohol/ sodium lauryl sulfate/sodium cetearyl sulfate, and paraffi num liquidum, bearing in mind that the presence of solid–solid interaction does not necessarily indicate incompatibility other analytical techniques were also used, such as IST/HPLC and FT-IR, which can gen- erally help in the interpretation of thermal results. The interaction of caprylic capric tri- glyceride, propylparaben, and BHT with avobenzone was confi rmed by IST/HPLC and FT-IR results. These results are in accordance with our accelerated stability studies in which avobenzone seemed to be less stable in the presence of caprylic capric triglyceride (36). The FT-IR technique did not indicate any incompatibility of avobenzone with ce- tearyl alcohol, isopropyl myristate, diethylhexyl syringylidene malonate, glycerin, cetea- ryl alcohol/ceteareth 20, cetearyl alcohol/sodium lauryl sulfate/sodium cetearyl sulfate, and paraffi num liquidum, considering that the absorption bands of avobenzone remained unchanged in the physical mixtures. ACKNOWLEDGMENTS This work was supported by grant B072 and 20020100100816 to A. I. Segall from UBA. The authors also thank Merck Química Argentina S.A.I.C. and Flamaquímica S.R.L. (Argentina) for the donation of an UV fi lter and reagents. REFERENCES 1. T. A. Júlio, I. F. Zâmara, J. S. Garcia, and M. G. Trevisan, Compatibility of sildenafi l citrate and phar- maceutical excipients by thermal analysis and LC–UV, J. Therm. Anal. Cal., 111, 2037–2044 (2012). DOI: 10.1007/s10973-012-2292-8. 2. B. Tita, A. Fulias, G. Bandur, E. Marian, and D. Tita, Compatibility study between ketoprofen and pharmaceutical excipients used in solid dosage forms, J. Pharm. Biomed. Anal., 56, 221–227 (2011). 3. K. Liltorp, T. Gorm Larsen, B. Willumsen, and R. Holm, Solid state compatibility studies with tablet excipients using non thermal methods, J. Pharm. Biomed. Anal., 55, 424–428 (2011). 4. F. Pires Maximiano, K. Monteiro Novack, M. T. Bahia, L. L. de Sá-Barreto, and M. S. Soares da Cunha- Filho, Polymorphic screen and drug–excipient compatibility studies of the antichagasic benznidazole, J. Therm. Anal. Cal., 106, 819–824 (2011). 5. M. J. Peres-Filho, M. Pedroso Nogueira Gaeti, S. Ramirez de Oliveira, R. Neves Marreto, and E. Martins Lima, Thermoanalytical investigation of olanzapine compatibility with excipients used in solid oral dosage forms, J. Therm. Anal. Cal., 104, 255–260 (2011). 6. Z. Aigner, R. Heinrich, E. Sipos, G. Farkas, A. Ciurba, O. Berkesi, and P. Szabó-Révész, Compatibility studies of aceclofenac with retard tablet excipients by means of thermal and FT-IR spectroscopic meth- ods, J. Therm. Anal. Cal., 104, 265–271 (2011). 7. M. A. Moyano, A. M. Broussalis, and A. I. Segall, Thermal analysis of lipoic acid and evaluation of the compatibility with excipients, J. Therm. Anal. Cal., 99, 631–637 (2010). 8. F. Monajjemzadeh, D. Hassanzadeh, H. Valizadeh, M. R. Siahi-Shadbad, J. Shahbazi Mojarrad, T. A. Robertson, and M. S. Roberts, Compatibility studies of acyclovir and lactose in physical mixtures and commercial tablets, Eur. J. Pharm. Biopharm., 73, 404–413 (2009). 9. L. Harding, S. Qi, G. Hill, M. Reading, and D. Q. M. Craig, The development of microthermal analy- sis and photothermal microspectroscopy as novel approaches to drug–excipient compatibility studies, Int. J. Pharm., 354, 149–157 (2008). 10. S. Agatonovic-Kustrin, N. Markovic, M. Ginic-Markovic, M. Mangan, and B. D. Glass, Compatibility studies between mannitol and omeprazole sodium isomers, J. Pharm. Biomed. Anal., 48, 356–360 (2008).