What breastfeeding precautions apply to Cystadrops (mercaptamine hydrochloride) eye drops when oral cysteamine is also taken?

Women using Cystadrops (mercaptamine hydrochloride) eye drops alongside oral cysteamine should not breastfeed because cysteamine excretion into human milk is unknown and animal studies in breastfeeding mothers and neonates underpin this precaution, despite negligible systemic exposure from eye drops.