mercaptamine hydrochloride: clinical use

Prescribing considerations

• Initiate under a physician experienced in managing cystinosis.
• Avoid unplanned discontinuation because corneal crystal accumulation can increase.
• Systemic exposure from ocular administration is expected to be low.
• Safety and efficacy have not been established below 6 months of age.

Contraindications and cautions

• Hypersensitivity to cysteamine or any excipient.
• Use caution with soft contact lenses, dry eye or existing corneal disorders because the product contains benzalkonium chloride.

Monitoring

• Ophthalmic assessment of corneal crystal deposits and photophobia.
• Local tolerability, including pain, redness, blurred vision and eyelid reactions.
• Corneal surface changes associated with benzalkonium chloride, including punctate or ulcerative keratopathy.

Clinical pharmacology

Cysteamine is a cystine-depleting agent that converts cystine into cysteine and cysteine–cysteamine mixed disulfides. Ocular pharmacokinetic studies have not been performed; some systemic absorption may occur, but exposure is expected to be low.

Formulation and product differences

• The selected licensed product is a clear, viscous, preserved eye-drop solution supplied with a separate dropper applicator.
• It contains benzalkonium chloride, which can irritate the eye and be absorbed by or discolour soft contact lenses.
• Before opening it requires refrigerated, light-protected storage. Once opened, it is kept below 25°C, protected from light, not refrigerated and discarded after 7 days.

Eye drops

Route: Ophthalmic

Strengths: 3.8 mg/mL