Physico-chemical stability study of a sodium thiosulphate gel

S. Molignier 1, E. Caudron2,3 K. Kemel3, C. Laugel3, J. Jost1,4, V. Guigonis5,6, V. Ratsimbazafy1,4 1 Service Pharmacie, CHU Dupuytren, Limoges, France
2 Service Pharmacie, Hôpital européen Georges Pompidou, AP-HP, Paris, France
3 Lip(Sys)2, Chimie analytique pharmaceutique, Université Paris Sud, Paris Saclay, Chatenay-Malabry, France.
4 UMR 1094, Université de Limoges, France
5 Service de Pédiatrie, CHU Dupuytren, Limoges, France
6 UMR 7276, Université de Limoges, France

Introduction

In a previous study, a sodium thiosulphate (TSS) gel was developed to enhance skin penetration and treatment of ectopic calcifications. To pursue the development of this formulation, we aimed to study the physicochemical stability of this new TSS topical form.

Material and method

The study protocol was developed using the GERPAC guideline for stability studies. Physicochemical stability was evaluated on 3 months (T0, T1, T3, T8, T16, T30, T60 and T90) with several evaluation parameters: visual aspect, organoleptic properties, pH (n = 3) and TSS content (n = 6). Previously, an HPLC-UV had been validated to assess TSS content and presence of TSS impurities. To assess the physicochemical stability, a 25% TSS gel was compounded and separated into plastic bottles; 7 samples were stored at 25°C and 7 at 4°C, out of direct light.

All results were evaluated with respect to them obtained at D0. Maximum deviation ratio was set at 5% for pH and 10% for TSS. Color was compared with photos. Regarding odor, comparison was not achievable and only the characteristic odor of TSS degradation product (H2S) was searched.

Results

After 90 days of study, all evaluation parameters remained stable whatever the storage condition used. Macroscopic aspect remained unchanged: translucent white color. Characteristic odor of the degradation product of TSS (H2S) was not detected and pH remained around ± 5% of the initial value.

The mean recovery rate of TSS remained around ± 10% the initial value. At the end of the study (T90), the mean recovery rate of TSS was 104±2% at 25°C and 103±2% at 4°C. No TSS degradation product was found.

Discussion - Conclusion

Regarding the results of the physicochemical stability study, this new formulation has demonstrated its capacity to remain stable over a 90-day period at 25°C or 4°C. We now aim to assess the microbiological stability of this TSS gel to be able to perform human testing.

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