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Question

Posted on: April 11 2017

In a W/O cream are prescribed after thiosulfate crystals. Why crystals?

R/Na thiosulfate crystals 25g, zinc oxide 5g, water-containing Vaseline ad 100g. Is it important that the crystals are? Can it also be the 6. H2O variant? Are there any other details of this preparation? (Method of preparation, preservation,...)

Answer

I find no indication of a variant with 6 AQ but with 5 aq. This is crystalline and soluble 1 part in 0.6 parts water.  

In A cream one would normally expect the powder but here it is intended to dissolve the thiosulfate in water.  

Whether there is a difference in solubility between powder and crystalline is not reflected. Both are listed as soluble in water. I don't know which thiosulfate can be purchased.  

I cannot express my opinion on the shelf life. Thiosulfate is not very stable in water anyway and here ZnO will inevitably make the water phase Alcalisch.   So????

We could recommend a storage in the fridge but here we run the risk of crystallization. So just keep it cool. I think that as a magistal preparation with a retention period of 2 months, the shelf life should not cause any major problems. So do not store in the closet and after x months top up again.