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In three clinical trials, cysteamine or phosphocysteamine have been administered to 246 children with cystinosis. Causality of side effects is sometimes difficult to determine because adverse effects may result from the underlying disease.

The most frequent adverse reactions seen involve the gastrointestinal and central nervous systems. These are especially prominent at the initiation of cysteamine therapy. Temporarily suspending treatment, then gradual re-introduction may be effective in improving tolerance.

Adverse reactions were not collected systematically in the NCCS, but were often listed by investigators. The following rates may therefore be underestimated. The most common events (> 5%) were vomiting 35%, anorexia 31%, fever 22%, diarrhea 16%, lethargy 11%, and rash 7%.

Less common adverse events are:

Body as a whole: Dehydration.

Cardiovascular: Hypertension.

Digestive: Nausea, bad breath, abdominal pain, dyspepsia, constipation, gastroenteritis, duodenitis, gastrointestinal ulceration and bleeding.

Central Nervous System: Somnolence, encephalopathy, headache, seizures, ataxia, confusion, tremor, hyperkinesia, decreasing hearing, dizziness, jitteriness.

Psychiatric: Nervousness, abnormal thinking, depression, emotional lability, hallucinations, nightmares.

Integumentary: Urticaria.

Urogenital: Interstitial nephritis, renal failure (see WARNINGS).

Clinical Laboratory: Abnormal liver function, anemia, leukopenia.

Adverse reactions or intolerance leading to cessation of treatment occurred in 8% of patients in the U.S. Studies.

Withdrawals due to intolerance, vomiting associated with medication, anorexia, lethargy, and fever appeared dose related, occurring more frequently in those patients receiving 1.95 grams/m2/day as compared to 1.30 grams/m2/day.

  Dose in Grams/m2/day
(n = 42)
(n = 51)
Vomiting Considered Related to Medicine 31 67
Anorexia 33 51
Lethargy 17 27
Diarrhea 31 31
Fever 28 45

Sudden deaths have been reported in this disease state.

Post-marketing surveillance

Benign intracranial hypertension (or pseudotumor cerebri; PTC) with papilledema; skin lesions, molluscoid pseudotumors, skin striae, skin fragility; joint hyperextension, leg pain, genu valgum, osteopenia, compression fracture and scoliosis have been reported (see PRECAUTIONS).

Drug Abuse and Dependence

CYSTAGON® (cysteamine bitartrate) has not been associated with abuse potential, psychological or physical dependence in humans.