Mercaptamine Other names: Cysteamine

Mercaptamine reduces corneal cystine crystal accumulation acting as a cystine-depleting agent by converting cystine to cysteine and cysteine-cysteamine mixed disulfides.

Human pharmacokinetic assessment following ocular administration of mercaptamine was not performed.

Similarly to other topically administered ocular products, systemic absorption is likely to occur. However it should be considered that the recommended daily dose of mercaptamine applied as eye drops is no more than approximately 0.4% of the highest recommended daily oral dose of mercaptamine in any age group.

Systemic exposure following ocular administration is anticipated to be low. When there is concomitant use of ocular and oral treatment with mercaptamine the contribution to any systemic risk from ocular administration is considered negligible.

Preclinical data on oral mercaptamine

Genotoxicity studies have been performed: induction of chromosome aberrations in cultured eukaryotic cell lines has been reported and specific studies with mercaptamine did not show any mutagenic effects in the Ames test or any clastogenic effect in the mouse micronucleus test.

Reproduction studies showed embryofoetotoxic effects (resorptions and post-implantation losses) in rats at the 100 mg/kg/day dose level and in rabbits receiving mercaptamine 50 mg/kg/day. Teratogenic effects have been described in rats when mercaptamine is administered over the period of organogenesis at a dose of 100 mg/kg/day.

This is equivalent to 0.6 g/m²/day in the rat, which is less than half the recommended clinical maintenance dose of mercaptamine, i.e. 1.30 g/m²/day. A reduction of fertility was observed in rats at 375 mg/kg/day, a dose at which body weight gain was retarded. At this dose, weight gain and survival of the offspring during lactation was also reduced. High doses of mercaptamine impair the ability of lactating mothers to feed their pups. Single doses of the drug inhibit prolactin secretion in animals.

Administration of mercaptamine in neonate rats induced cataracts.

High doses of mercaptamine, either by oral or parenteral routes, produce duodenal ulcers in rats and mice but not in monkeys. Experimental administration of the drug causes depletion of somatostatin in several animal species. The consequence of this for the clinical use of the drug is unknown.

No carcinogenic studies have been conducted with mercaptamine.