Cystagon (Cysteamine Bitartrate)
Cystine-depleting agent for nephropathic cystinosis
Cystagon (cysteamine bitartrate) is an orphan drug prescribed for the treatment of nephropathic cystinosis, a rare inherited metabolic disorder. Cystinosis causes the amino acid cystine to accumulate within cells, leading to progressive damage to the kidneys, eyes, muscles, pancreas, and brain. Cystagon works by chemically reacting with cystine inside cells, lowering cystine levels and slowing organ damage. Treatment is lifelong and requires regular monitoring of white blood cell cystine levels.
Quick Facts: Cystagon
Key Takeaways
- Cystagon is a lifelong treatment for nephropathic cystinosis, a rare inherited disorder causing cystine accumulation in cells.
- The drug is taken 4 times daily, every 6 hours, with or immediately after food. The dose is based on body surface area in children.
- Regular blood tests to monitor white blood cell cystine levels are essential to ensure the correct dose and treatment efficacy.
- Cystagon must not be used during pregnancy (especially the first trimester), during breastfeeding, or by patients allergic to cysteamine or penicillamine.
- Common side effects include nausea, vomiting, diarrhoea, loss of appetite, and body odour. Serious side effects such as skin changes and bone abnormalities require immediate medical attention.
What Is Cystagon and What Is It Used For?
Nephropathic cystinosis is one of the rarest inherited metabolic disorders, affecting approximately 1 in 100,000 to 200,000 live births worldwide. It belongs to a group of conditions known as lysosomal storage disorders, caused by mutations in the CTNS gene on chromosome 17p13. This gene encodes the protein cystinosin, which is responsible for transporting cystine out of lysosomes. When cystinosin is absent or dysfunctional, free cystine accumulates within lysosomal compartments, eventually forming crystals that damage cells and tissues throughout the body.
The disease typically manifests in three clinical forms. Infantile (nephropathic) cystinosis is the most severe and most common form, presenting in the first year of life with symptoms of renal Fanconi syndrome — excessive loss of glucose, amino acids, phosphate, bicarbonate, and other electrolytes in the urine. Without treatment, progressive kidney failure typically occurs by the age of 10. Juvenile (intermediate) cystinosis presents later in childhood with milder symptoms. Ocular (adult) cystinosis affects only the eyes, causing photophobia due to corneal cystine crystal deposition.
Cystagon contains the active substance cysteamine (as its bitartrate salt, also known as mercaptamine bitartrate). Cysteamine is a small aminothiol molecule that can enter lysosomes and react with cystine. This chemical reaction converts cystine into two compounds — cysteine and a cysteamine-cysteine mixed disulfide — both of which can exit the lysosome through alternative transport systems that do not require cystinosin. By providing an escape route for trapped cystine, cysteamine effectively lowers the toxic intracellular cystine burden.
Clinical studies have demonstrated that early and consistent cysteamine therapy can significantly delay the progression of kidney damage, reduce the need for kidney transplantation, preserve thyroid function, and improve growth in children with cystinosis. According to long-term follow-up data published by the National Institutes of Health (NIH), patients who start cysteamine therapy early and maintain good adherence can preserve kidney function for decades longer than untreated patients. However, cysteamine does not reverse damage that has already occurred, which is why early diagnosis and initiation of treatment are critical.
It is important to note that Cystagon does not prevent the accumulation of cystine crystals in the eyes. If cysteamine eye drops have been prescribed, that treatment should be continued alongside oral Cystagon therapy. Eye drops containing cysteamine (such as Cystadrops) are needed separately to dissolve corneal cystine crystals and relieve photophobia.
What Should You Know Before Taking Cystagon?
Contraindications
Cystagon must not be used if you or your child has a known allergy (hypersensitivity) to cysteamine bitartrate, penicillamine, or any of the other ingredients listed in the product information. Cross-sensitivity between cysteamine and penicillamine is well documented because both molecules contain thiol (sulfhydryl) groups, and patients who have experienced allergic reactions to penicillamine should not be started on cysteamine without careful medical evaluation.
The drug is strictly contraindicated during pregnancy, particularly during the first trimester. Animal reproductive studies have shown adverse effects on foetal development, and there is insufficient human data to establish safety. Women of childbearing potential must use effective contraception during treatment. If pregnancy is planned, patients should discuss the risks and benefits with their treating physician well in advance.
Breastfeeding is also contraindicated during Cystagon therapy. It is not known whether cysteamine passes into human breast milk, but given the drug's mechanism of action and potential toxicity, the risk to a nursing infant cannot be excluded.
Warnings and Precautions
Once the diagnosis of cystinosis has been confirmed through leukocyte (white blood cell) cystine measurements, treatment with Cystagon should be started as soon as possible. The earlier treatment begins, the greater the potential benefit in terms of preserving organ function. Ideally, treatment should commence before the onset of significant kidney damage.
Skin and bone monitoring is essential. A small number of cases of skin changes on the elbows — described as small, hard lumps (papules) — have been reported in children treated with high doses of various cysteamine preparations. These skin lesions have been associated with stretch marks (striae), bone abnormalities including fractures and bone deformities, and joint hypermobility. Your doctor may request regular physical examinations and X-ray imaging of the skin and skeleton to monitor for these effects. If any changes in skin or bone are noticed, contact your doctor immediately and the dose may need to be reduced.
Regular blood cell counts should be monitored, as cysteamine may affect white blood cell counts. Your doctor will arrange routine blood tests as part of ongoing monitoring. Liver function tests should also be performed periodically, as abnormal liver function test results have been reported as a common side effect.
Do not give whole capsules to children under approximately 6 years of age, as there is a risk of the capsule entering the windpipe (aspiration). For younger children, open the capsule and sprinkle the contents on food. Do not swallow the desiccant container found inside the bottle.
Unlike phosphocysteamine (another cysteamine-containing compound), Cystagon does not contain phosphate. If you are already being treated with phosphate supplements, the dose of these supplements may need to be adjusted when switching from phosphocysteamine to Cystagon. Your doctor should review all supplement dosages during the transition.
Pregnancy and Breastfeeding
Pregnancy: Cystagon must not be used during pregnancy. This is particularly critical during the first trimester, when the risk of teratogenic effects is highest. Preclinical studies in animals have demonstrated embryotoxic and fetotoxic effects of cysteamine. Women of childbearing age should be counselled about the importance of effective contraception before starting treatment. If you are planning to become pregnant, discuss this with your doctor — the decision to discontinue treatment must be weighed against the serious consequences of untreated cystinosis, and specialist advice is essential.
Breastfeeding: Cystagon must not be used during breastfeeding. The potential risks to the nursing infant are unknown but cannot be excluded given the pharmacological properties of the drug. Mothers requiring cysteamine therapy should be advised to use appropriate alternatives to breast milk.
Driving and Operating Machinery
Cystagon may cause drowsiness and reduce alertness in some patients. When starting treatment, patients should not engage in potentially hazardous activities such as driving a car or operating heavy machinery until the effects of the drug are known. If drowsiness persists, discuss this with your doctor, as dose adjustment or timing of administration may help.
Drug Interactions
Tell your doctor or pharmacist if you are taking, have recently taken, or might take any other medicines. While there are no widely reported major drug interactions with cysteamine, the following considerations apply:
- Phosphate supplements: Dose adjustment may be necessary when switching between cysteamine preparations with different phosphate content.
- Electrolyte supplements: Patients with cystinosis typically take multiple supplements (potassium, bicarbonate, carnitine, vitamin D). All supplement dosages should be carefully coordinated with the treating physician.
- Alcohol: May worsen gastrointestinal side effects and drowsiness. Avoid alcohol during treatment.
- Acidic beverages: Do not mix capsule contents with acidic drinks such as orange juice, as acidity may affect the stability and absorption of cysteamine.
What Is the Correct Dosage of Cystagon?
Always use Cystagon exactly as your doctor has told you. The dosage is carefully calculated based on your or your child's age and body size. Do not increase or decrease the dose without your doctor's explicit approval. Regular blood tests measuring the cystine content in white blood cells are essential to guide dose adjustments and ensure that intracellular cystine levels are maintained below the therapeutic target.
Children (Up to 12 Years)
Paediatric Dosing
The dose is calculated based on body surface area (BSA). The usual recommended dose is 1.30 g/m² of body surface area per day, divided into 4 equal doses given every 6 hours. Treatment is typically initiated at a lower dose (one-quarter to one-sixth of the target dose) and gradually increased over 4–6 weeks to minimise gastrointestinal side effects.
For children under approximately 6 years who cannot swallow capsules, the hard capsules may be opened and the contents sprinkled onto food such as milk, mashed potato, or starch-based food, or mixed into infant formula. Do not mix with acidic drinks such as orange juice.
Adolescents and Adults (Over 12 Years, >50 kg)
Adult Dosing
The usual dose for patients over 12 years of age and weighing more than 50 kg is 2 g per day, divided into 4 doses of 500 mg each, taken every 6 hours. This dose should be adjusted based on white blood cell cystine level monitoring.
Maximum Dose
The daily dose must not exceed 1.95 g/m²/day under any circumstances. Higher doses have been associated with an increased risk of serious side effects including skin changes, stretch marks, and bone abnormalities.
| Patient Group | Recommended Daily Dose | Frequency | Notes |
|---|---|---|---|
| Children up to 12 years | 1.30 g/m²/day | 4 times daily (every 6 hours) | Based on body surface area; gradual dose escalation |
| Adolescents >12 years (>50 kg) | 2 g/day (500 mg × 4) | 4 times daily (every 6 hours) | Adjust based on WBC cystine levels |
| Maximum dose (all ages) | 1.95 g/m²/day | 4 times daily (every 6 hours) | Must not be exceeded |
How to Take Cystagon
Cystagon should be taken by mouth only. Follow the timing schedule as closely as possible — the 6-hourly intervals are important to maintain consistent drug levels and sustained cystine depletion. Take each dose with or immediately after food to reduce gastrointestinal side effects.
Your treatment will likely include additional supplements to replace electrolytes and nutrients lost through the kidneys. These may include potassium citrate or bicarbonate, phosphate supplements, carnitine, and vitamin D. It is critical that all supplements are taken exactly as instructed. If multiple doses of supplements are missed, or if weakness or lethargy develops, contact your doctor immediately.
Regular blood tests to measure the cystine content in white blood cells (leukocytes) are necessary to determine and adjust the correct Cystagon dose. Your doctor will also arrange tests to measure levels of important electrolytes in your blood and urine. The therapeutic target is a white blood cell cystine level below 1 nmol half-cystine/mg protein. These tests are typically performed every 3 months once a stable dose has been achieved.
Missed Dose
If a dose is missed, take it as soon as you remember. However, if less than 2 hours remain until the next scheduled dose, skip the missed dose and return to the regular dosing schedule. Do not take a double dose to compensate for a missed dose. Consistent adherence to the dosing schedule is important for maintaining therapeutic cystine depletion, so try to set reminders or alarms to help with the every-6-hours regimen.
Overdose
If more Cystagon has been taken than prescribed, or in case of accidental overdose, contact your doctor or the nearest hospital emergency department immediately. Symptoms of overdose may include excessive drowsiness, lethargy, and exacerbation of typical side effects such as nausea and vomiting. Supportive care and monitoring are the mainstays of overdose management. There is no specific antidote for cysteamine overdose.
What Are the Side Effects of Cystagon?
Like all medicines, Cystagon can cause side effects, although not everyone will experience them. The side effects listed below have been observed during clinical use and post-marketing surveillance. Many patients find that gastrointestinal side effects are most troublesome during the initial weeks of treatment and may improve with gradual dose escalation and consistent administration with food.
Cystagon is known to cause drowsiness and may reduce alertness. Ensure that you or your child understand how the medication affects you before participating in any activities that require full attention, such as driving, cycling, or operating machinery.
Very Common
Affects more than 1 in 10 patients
- Vomiting
- Nausea
- Diarrhoea
- Loss of appetite (anorexia)
- Fever
- Drowsiness (somnolence)
Common
Affects 1 in 10 to 1 in 100 patients
- Abdominal pain or discomfort
- Bad breath (halitosis) and body odour
- Skin rash
- Gastroenteritis
- Fatigue
- Headache
- Encephalopathy (brain disorder)
- Abnormal liver function tests
Uncommon
Affects 1 in 100 to 1 in 1,000 patients
- Stretch marks (striae)
- Skin changes (small hard lumps on the elbows)
- Joint hypermobility
- Bone pain and fractures
- Scoliosis (curvature of the spine)
- Bone deformities and fragility
- Hair discolouration
- Severe allergic reaction (anaphylaxis)
- Seizures (convulsions)
- Nervousness
- Hallucinations
- Decreased white blood cell count (leukopenia)
- Gastrointestinal ulcers with bleeding
- Kidney problems (swelling of extremities, weight gain)
Because some of these side effects are serious, it is important to ask your doctor or your child's doctor to explain any warning signs to watch for. In particular, any new skin changes (especially on the elbows), bone pain, or signs of allergic reaction should be reported immediately. The gastrointestinal side effects (nausea, vomiting, diarrhoea) typically improve with time and can be managed by taking the medication with food. The characteristic body odour associated with cysteamine treatment is caused by the sulfur-containing nature of the molecule and may be partially managed by bathing regularly and using unscented body products.
It is important to report suspected side effects after the medicine has been authorised. This allows ongoing monitoring of the medicine's benefit-risk balance. Healthcare professionals and patients can report suspected adverse reactions to their national pharmacovigilance authority — for example, the EMA (Europe), FDA MedWatch (USA), or MHRA Yellow Card Scheme (UK).
How Does Cystagon Interact with Other Drugs?
While cysteamine does not have a long list of major drug interactions in the traditional pharmacological sense, the complexity of managing cystinosis means that treatment regimens often involve multiple concurrent therapies. Careful coordination between all medications is essential to avoid under- or over-supplementation, gastrointestinal complications, and therapeutic interference.
| Substance | Type | Effect | Recommendation |
|---|---|---|---|
| Phosphate supplements | Dose adjustment | Cystagon lacks phosphate (unlike phosphocysteamine) | Adjust phosphate dose when switching preparations |
| Bicarbonate / potassium supplements | Monitoring | Essential for Fanconi syndrome management | Do not skip doses; contact doctor if missed |
| Penicillamine | Contraindication | Cross-sensitivity risk due to shared thiol group | Avoid if history of penicillamine allergy |
| Alcohol | Caution | May worsen drowsiness and GI side effects | Avoid during treatment |
| Acidic beverages (orange juice) | Administration | May reduce stability and absorption | Do not mix capsule contents with acidic drinks |
| Indomethacin / NSAIDs | Caution | May increase risk of GI ulceration | Use with caution; monitor for GI bleeding |
Always inform your doctor, pharmacist, or specialist of all medications and supplements you or your child are taking. This includes over-the-counter medicines, herbal preparations, and dietary supplements. Because cystinosis patients often require a complex regimen of multiple medications and supplements, a comprehensive medication review should be performed at each clinical visit.
How Should You Store Cystagon?
Proper storage of Cystagon is essential to maintain the medication's effectiveness and safety. Cysteamine bitartrate is sensitive to environmental conditions, and improper storage can lead to degradation of the active ingredient.
- Temperature: Store at or below 25°C (77°F). Do not refrigerate or freeze.
- Light: Protect from light. Keep capsules in the original bottle.
- Moisture: Protect from moisture. Keep the bottle tightly closed. Do not remove the desiccant container found inside the bottle — it helps absorb excess moisture.
- Keep out of reach of children: Store in a location inaccessible to young children.
- Expiry date: Do not use Cystagon after the expiry date printed on the label. The expiry date refers to the last day of the stated month.
- Disposal: Do not dispose of Cystagon in household waste or via drains. Ask your pharmacist about proper disposal methods to protect the environment.
Cystagon capsules are supplied in bottles containing 100 or 500 hard capsules. Not all pack sizes may be available in your country. The bottles feature a child-resistant closure. To open, place a pen or similar object between the raised portions of the lid and turn anticlockwise. To close, turn clockwise.
What Does Cystagon Contain?
Active Ingredient
Each hard capsule of Cystagon contains cysteamine in the form of mercaptamine bitartrate (cysteamine bitartrate). The drug is available in two strengths:
- Cystagon 50 mg: White, opaque hard capsules marked "CYSTA 50" on the body and "RECORDATI RARE DISEASES" on the cap.
- Cystagon 150 mg: White, opaque hard capsules marked "CYSTAGON 150" on the body and "RECORDATI RARE DISEASES" on the cap.
Inactive Ingredients (Excipients)
| Ingredient | Function |
|---|---|
| Microcrystalline cellulose | Filler / diluent |
| Pregelatinised starch | Binder / disintegrant |
| Magnesium stearate / sodium lauryl sulfate | Lubricant |
| Colloidal silicon dioxide | Glidant |
| Croscarmellose sodium | Disintegrant |
| Gelatin (capsule shell) | Capsule shell |
| Titanium dioxide (E171) | Capsule colourant (white) |
| Iron oxide black ink (E172) | Capsule printing ink |
Marketing Authorisation Holder and Manufacturer
Cystagon is manufactured and marketed by Recordati Rare Diseases, a pharmaceutical company specialising in orphan drugs and treatments for rare diseases. The company is headquartered in Puteaux, France. Further information about Cystagon can be found on the European Medicines Agency (EMA) website, where the full European Public Assessment Report (EPAR) is available.
Frequently Asked Questions About Cystagon
Nephropathic cystinosis is a rare inherited metabolic disorder caused by mutations in the CTNS gene. It leads to accumulation of the amino acid cystine within lysosomes (cellular recycling compartments) throughout the body. Without treatment, cystine crystals progressively damage the kidneys, eyes, thyroid, muscles, pancreas, and central nervous system. The kidneys are typically affected first, with symptoms of Fanconi syndrome (excessive loss of nutrients in urine) appearing in the first year of life. Without cysteamine therapy, most patients develop end-stage kidney failure by age 10. Early and consistent treatment with Cystagon can significantly delay kidney damage and preserve function in other organs.
Cystagon begins lowering intracellular cystine levels within hours of the first dose. However, the clinical benefits of treatment are seen over months and years, as the goal is to prevent progressive organ damage. White blood cell cystine levels are typically checked 5–6 hours after a dose to assess whether therapeutic targets are being met. It may take several weeks of dose adjustment to achieve optimal cystine depletion. The drug does not reverse existing organ damage, which is why early initiation of treatment is so important.
No. Oral Cystagon does not effectively penetrate the cornea and therefore cannot prevent or treat cystine crystal accumulation in the eyes. Patients with cystinosis typically require separate cysteamine eye drops (such as Cystadrops) applied directly to the eyes to dissolve corneal cystine crystals and relieve symptoms of photophobia (light sensitivity). Both oral capsules and eye drops should be used as part of a comprehensive treatment plan.
Cysteamine is a sulfur-containing compound (aminothiol). When metabolised in the body, it produces volatile sulfur compounds that are excreted through sweat, breath, and urine, resulting in the characteristic unpleasant odour. This side effect is related to the drug's mechanism of action and cannot be completely eliminated. However, strategies to manage the odour include regular bathing, using unscented deodorants, taking the medication with food, and discussing dose timing with your doctor. Some patients find that the odour decreases somewhat over time.
Stopping Cystagon treatment leads to renewed accumulation of cystine within cells, and the progressive organ damage associated with cystinosis will resume. Studies have shown that interruption of cysteamine therapy can result in a rapid increase in white blood cell cystine levels within days. Long-term non-adherence is associated with accelerated decline in kidney function and progression of extra-renal complications. Treatment with Cystagon is lifelong and should only be discontinued under the explicit guidance of a specialist physician, and only after careful consideration of the serious risks involved.
Cystagon has orphan drug designation in both the European Union and the United States, meaning it has been specifically developed and authorised for the treatment of a rare disease. It is available in many countries, though availability and reimbursement may vary. The drug is manufactured by Recordati Rare Diseases. Patients in countries where Cystagon is not directly available may be able to access it through compassionate use programmes, named-patient imports, or alternative cysteamine formulations. Your treating physician or a rare disease specialist can advise on access options in your region.
References
- European Medicines Agency (EMA). Cystagon – Summary of Product Characteristics (SmPC). Last updated November 2024. Available at: EMA EPAR – Cystagon.
- Gahl WA, Thoene JG, Schneider JA. Cystinosis. N Engl J Med. 2002;347(2):111–121. doi:10.1056/NEJMra020552.
- Langman CB, Barshop BA, Deschenes G, et al. Controversies and research agenda in nephropathic cystinosis: conclusions from a “Kidney Disease: Improving Global Outcomes” (KDIGO) Controversies Conference. Kidney Int. 2016;89(6):1192–1203.
- Nesterova G, Gahl WA. Nephropathic cystinosis: late complications of a multisystemic disease. Pediatr Nephrol. 2008;23(6):863–878.
- Elmonem MA, Veys KR, Soliman NA, et al. Cystinosis: a review. Orphanet J Rare Dis. 2016;11:47. doi:10.1186/s13023-016-0426-y.
- Markello TC, Bernardini IM, Gahl WA. Improved renal function in children with cystinosis treated with cysteamine. N Engl J Med. 1993;328(16):1157–1162.
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List. 2023. Available at: WHO Essential Medicines List.
- Ariceta G, Giordano V, Santos F. Effects of long-term cysteamine treatment in patients with cystinosis. Pediatr Nephrol. 2019;34(4):571–578.
- U.S. Food and Drug Administration (FDA). Cystagon Prescribing Information. Available at: FDA Drug Approvals.
- Recordati Rare Diseases. Cystagon Patient Information Leaflet. Last revised November 2024.
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