[Cystine calculi. In vitro solubility and chemical structure]

A series of cystine stones extracted from the same subject by pyelotomy was used to study the in vitro solubility of these stones in various solutions. Isotonic bicarbonated saline presented a definite dissolving action, but the stone dissolved relatively slowly alpha-mercapto-propionyl-glycine was much more active, even when mixed urine. N-acetylcystine had the same degree of effectiveness as alpha-mercapto-propionyl-glycine. One stone in this series, which was partially covered by a coating of calcium phosphate, dissolved much more slowly than the other stones. In subjects with cystine stones, longstanding large stones are frequently mixtures of phosphates and cystine and, in 21 cases, chemical analyses and infra-red spectrography demonstrated the presence of calcium phosphate on the surface or in the inferior of these stones, associated with ammoniaco-magnesium phosphate in three cases. The presence of phosphates makes oral medical treatment ineffective, but mixed stones are more friable than pure cystine stones and are therefore easier to treat by extracorporeal lithotripsy.