Question
Posted on: March 6 2013A prescription of a dermatologist for a beverage with cystine intended for a child aged 1.5 years
Answer
physico-chemical properties of cystine:
- soluble in water up to 0.01%
- soluble in acid and alkali with salt formation
- pKs1 (Carboxyl) = 1, pKs2 (Carboxyl) = 2.1, pKs3 (Amin) = 8.0, pKs4 = (Amin) 8.7
- pH of solution = 5.02
- dissolution in the Alcalisch middle
We therefore possess the ability to either acids or add base. Use of cystine solutions: mainly as eye drops 3.6%.
eye Drops formulation 360 mg in a small amount of water dissolving after adding 176 mg NaOH being 2.2 g of a 8.0% NaOH solution neutralization with 6.8 g of an isotonic boric acid solution (1.9%) Up to pH = 9.7 Supplement with physiologically serum up to 10 ml.
But for an oral preparation this composition does not seem so suitable. Personally, I would prefer to dissolve cystine with diluted acid. But the solubility of cystine at pH = 1 is equal to 170 mg/L. Consequently, there is only possibility of suspending cystine after prior grinding. I don't think that using cysteine HCl is a good solution considering this product in solution converts to cystine, which then crystallizes.