CYSTAGON

What it is

CYSTAGON is a cystine depleting agent which lowers the cystine content of cells in patients with cystinosis, an inherited defect of lysosomal transport. CYSTAGON contains mercaptamine (cysteamine) bitartrate and is available as capsules containing either 50 mg or 150 mg of mercaptamine free base.

Approved indications

— Management of nephropathic cystinosis in children and adults.

Dosing overview

The initial dose is 0.2 to 0.3 g/m² per day, given in four divided doses, increasing over 4 to 6 weeks to a maintenance dose of 1.3 g/m² per day given in four divided doses for children up to 12 years. Patients over 12 years old and 50 kg body weight should receive 2 g per day in four divided doses. The aim of therapy is to keep the leukocyte cystine concentration below 1 nmol of half-cystine/mg protein, 5 to 6 hours after administration of CYSTAGON. Intact capsules should not be administered to children under the age of approximately 6 years due to the risk of aspiration; the contents of the capsules may be sprinkled over food for children of this age.

Key safety warnings

Gastrointestinal tract symptoms including nausea, vomiting, anorexia and abdominal pain have been associated with mercaptamine, sometimes severe; in addition, gastrointestinal ulceration and bleeding have been reported in patients on mercaptamine bitartrate therapy, and physicians should remain alert for signs of ulceration and bleeding and inform patients and/or parents or guardians about the signs and symptoms of serious gastrointestinal toxicity and what steps to take if they occur. CNS symptoms such as seizures, lethargy, somnolence, depression and encephalopathy have been associated with mercaptamine; if CNS symptoms develop, the patient should be carefully evaluated and the dose adjusted as necessary. Patients should not engage in hazardous activities until the effects of CYSTAGON on mental performance are known. There have been post-marketing reports of serious skin lesions in patients treated with high doses of CYSTAGON or other mercaptamine salts that have responded to mercaptamine dose reduction; these skin lesions are purplish haemorrhagic lesions over the elbow area on both arms and have been described as molluscoid pseudotumors, and skin striae, bone lesions (that have been described as osteopenia, compression fractures, scoliosis and genu valgum) along with leg pain and joint hyperextension may also be present. Physicians should routinely monitor the skin and bones of patients receiving CYSTAGON, and if similar skin or bone abnormalities appear, the dose of CYSTAGON should be reduced. There have been post-marketing reports of benign intracranial hypertension (or pseudotumor cerebri) and/or papilledema associated with CYSTAGON treatment that has resolved with the addition of diuretic therapy; although a causal relationship has not been established, physicians should monitor patients for this condition and instruct patients to report headache, tinnitus, dizziness, nausea, diplopia, blurry vision, loss of vision, pain behind the eye or pain with eye movement, and a periodic eye examination is needed to identify this condition early and timely treatment should be provided when it occurs to prevent vision loss. Mercaptamine has occasionally been associated with reversible leukopenia and abnormal liver function studies; therefore, blood counts and liver function studies should be monitored.

Contraindications

CYSTAGON is contraindicated in patients who have developed hypersensitivity to it or to mercaptamine or penicillamine.

PBS listing

Information on PBS listing, including strength, item number, restriction type and ex-manufacturer price, is not available in the provided source documents.

Regulatory history

CYSTAGON was first registered on the Australian Register of Therapeutic Goods on 5 August 1997, with two strength variants: 50 mg capsules (ARTG 60451) and 150 mg capsules (ARTG 60452).