Formulation and clinical evaluation of carbidopa/levodopa oral solution for the treatment of sepiapterin reductase deficiency

Abstract

Background: sepiapterine reductase deficiency (SRD) is a rare levodopa (L-dopa)-responsive disorder treated with a combination therapy of controlled-release L-dopa and carbidopa. The currently available formulation of controlled-release carbidopa/L-dopa does not entirely meet the requirements for the long-term therapy in pediatric patients. In fact, administration of a manufactured tablet at a dose intended for adults necessitates its adjustment to the child's needs, as the splitting of the tablet into smaller portions or its dilution in water. It's essential to emphasize that tablets must not be crushed, as this can compromise the controlled-release mechanism and affect the efficacy of the medication. At the moment, commercial liquid formulations are not available. Given these limitations, in house drug preparation in hospitals and community pharmacies is a valid option to ensure the proper therapeutic management of these patients.

Materials and methods: we described sample preparation, physical and microbiological analyses, taste testing, and tolerability of a 1:10 ratio carbidopa/L-dopa flavored (mint, raspberry, cacao, berries) and unflavored oral formulation (no sweetening agents were added). We also reported long-term follow-up of two pediatric patients with SRD.

Results: we documented the stability for 28 days at 25 °C of the liquid solution. All formulations were well-tolerated, and no adverse events were observed during or after assessing taste and tolerability. The long-term follow up of two patients was characterized by effective symptom control and optimal treatment adherence and compliance.

Conclusions: in-house liquid drug formulations can be a valid option for pediatric patients with SRD. Given the significant impact of taste on medication adherence, the use of flavoring agents in the development of liquid formulations of L-dopa/carbidopa results a very useful strategy to obtain optimal adherence in the pediatric population.

Keywords: Adherence; Liquid oral flavored solution; Pediatric patients; Sepiapterin reductase deficiency.