Development of a carbocysteine 10% + urea 5% cream for the topical treatment of congenital ichthyosis

Lara González-Freire, María Carmen Dávila-Pousa, Ana Batalla-Cebey, Carlos Crespo-Diz

Optimization of a topical formula of N-acetylcysteine and urea for  the topical treatment of ichthyosis. We reviewed the chemical structure of the N-acetylcysteine molecule  and its metabolic processes. A search was conducted of possible alternative  molecules with a chemical structure similar to that of N-acetylcysteine that  could have improved organoleptic properties. The following databases were  used: PubChem®, Botplus®, the Drug Information Centre of the Spanish  Agency of Medicines and Medical Devices. The molecule selection criteria were  as follows: structural similarity, same therapeutic group, same mechanism of  action, same authorized indication, absence of unpleasant smell, and being  marketed as raw material in Spain. To complete the pharmaceutical  development and validation of the compound, several tests and controls were  conducted following the emulsion production procedure of the National  Formulary. In order to establish the validity period, we followed the  recommendations of the "Guide to Good Drug Preparation Practices in Hospital  Pharmacy Services". N-acetylcysteine has a free sulfhydryl group, which is responsible for  its smell, and undergoes deacetylation. Its main metabolites are cystine and  cysteamine. The following molecules were assessed: cystine, cysteamine,  carbocisteine, cysteine and methionine. Carbocisteine was selected because it met all the selection criteria. Carbocisteine is  ractically insoluble in water and soluble in mineral acids and alkaline hydroxides solutions. Unlike N-acetylcysteine, it does not have a fetid smell. It reaches its  maximum stability at pH 5.5 to 7.5. The composition of the compound (100 g)  was as follows: carbocisteine (10 g), urea (5 g), glycerine (15 g), water (44  mL), sodium hydroxide (1 g), and Neo PCL® Oil/Water (O/W) (25 g). It has an expiration period of 30 days. The organoleptic characteristics, emulsion type,  and pH remained stable within the established expiration period. The  arbocisteine compound has been incorporated into the group of topical  treatments available for the treatment of patients with ichthyosis in our  hospital. The carbocisteine molecule is a good therapeutic alternative that  lacks the unpleasant smell of N-acetylcysteine. The  arbocisteine compound developed has been included as topical treatment for  ichthyosis due to its tolerability, acceptability, and effectiveness in the  treatment of patients affected by this genodermatosis.