# A Comparative Pharmacokinetic Study for Cysteamine-Containing Eye Drops as an Orphan Topical Therapy in Cystinosis

## TL;DR

This study compares commercial and compounded cysteamine eye drops for treating cystinosis, focusing on their pharmacokinetics and physicochemical properties.

## Contribution

The study provides a comprehensive pharmacokinetic and physicochemical comparison of commercial and compounded cysteamine eye drops for cystinosis.

## Key findings

- Magistral cysteamine eye drops show potential as viable alternatives to commercial products.
- Pharmacokinetic and physicochemical tests reveal differences in drug release and mucoadhesivity.
- Statistical analysis supports the need for optimized formulations in cystinosis treatment.

## Abstract

Cystinosis is a low-prevalence lysosomal storage disease. The pathomechanism involves abnormal functioning of the cystinosine lysosomal cystine transporter (CTNS), causing intraliposomal accumulation of the amino acid cysteine disulfide, which crystallizes and deposits in several parts of the body. The most common ophthalmic complication of cystinosis is the deposition of “gold dust” cystine crystals on the cornea, which already occurs in infancy and leads to severe photosensitivity and dry eyes as it gradually progresses with age. In the specific treatment of cystinosis, preparations containing cysteamine (CYA) are used. The availability of commercialized eyedrops for the targeted treatment is scarce, and only Cystadrops® are commercially available with strong limitations. Thus, magistral CYA-containing compounded eyedrops (CYA-CED) could have a key role in patient care; however, a rationally designed comprehensive study on the commercialized and magistral products is still missing. This work aims to build up a comprehensive study about commercialized and magistral CYA eye drops, involving pharmacokinetic and physicochemical characterization (applying mucoadhesivity, rheology test, investigation of drug release, and parallel artificial membrane permeability assays), as well as ex vivo tests, well supported by statistical analysis.