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Effect of Latex and Plasticizer Concentration on Glucocorticoid Release from Ointments

María Adolfina Ruiz^a, Visitación Gallardo^a, Jose Luis Arias^a, and Angel Delgado^b

Department of Pharmacy and Pharmaceutical Technology, School of Pharmacy^a, and Department of Applied Physics, School of Sciences^b, University of Granada, Granada (Spain)

The in vitro release of two glucocorticoids, betamethasone disodium phosphate (BMNaP) and betamethasone acetate (BMA), is analyzed as a function of time in formulations containing Aquacoat (ethylcellulose latex) and cetylic excipient. An effect of the latex concentration is only observable in BMNaP formulations; the larger the latex concentration the faster the release rate. It is suggested that the aqueous solubility of BMNaP can account for this result; the availability of the corticoid is higher when the aqueous phase fraction in the system is larger. Unlike BMNaP, BMA availability is low whatever the latex concentration in the formulation; since BMA is insoluble in both the aqueous phase and the lipophobic excipient, the relationship between solubility and release behaviour is confirmed. In order to achieve a better control on the release characteristics of the formulation, the effect of the addition of the plasticizers, dibutyl phtalate and propylene glycol, to the ointments is also investigated.

Key words Betamethasone acetate, ointments, release · Betamethasone phosphate, ointments, release · Corticoids, topical preparations · Latex · Plasticizers