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Background and Importance Calciphylaxis is characterised by calcification of the middle layer of small arteries and arterioles, leading to painful skin lesions that progress to ulcers, mainly in the lower limbs. Thiosulphate acts as an antioxidant and vasodilator, providing rapid pain relief, and as a calcium salt chelator. It is not commercially available in our country and is used mainly as an intravenous magistral formula, although it is also used intralesionally and topically.Aim and Objectives Study the galenic and microbiological stability of a 25% sodium thiosulphate gel formulation.Material and Methods Sodium thiosulphate 5H2O Ph. Eur. 25.00 g Sodium carmellose Ph. Eur. 2.50 g Purified water Ph. Eur. q.s 100.00 g Tests performed for galenic stability study:Physical and organoleptic characteristics: colour, odour, evanescence, apparent extensibility, apparent consistency and transparency.Existence of aggregates.Existence of exudation.Determination of pH.Test performed for microbiological stability study: growth of aerobic (environmental) microorganisms.The samples are kept at ambient temperature (TA) (22-25°C) and in a refrigerator (4-8°C) in opaque plastic containers, with checks carried out on days 1, 6, 13, 35, 42, 48 and 51 after preparation.Results TA samples: all maintained their colour (colourless), odour (slightly plastic), evanescence (very high), apparent extensibility (very high), apparent consistency (medium) and transparency (transparent) from day 1 to day 51.Refrigerated samples: all maintained their colour (colourless), odour (practically odourless), evanescence (very high), apparent extensibility (very high), apparent consistency (medium–high) and transparency (transparent) from day 1 to day 51.None of the samples, either at room temperature or refrigerated, showed aggregates or exudation, all maintained a pH of 6.5 (within the maximum stability pH of sodium thiosulphate: 6-8.4) and the aerobic bacteria culture was negative from day 1 to day 51.Conclusion and Relevance Our 25% thiosulphate gel formula has proven to be stable from a galenic and microbiological point of view for at least 51 days at both room temperature and refrigerated.Conflict of Interest No conflict of interest