Procysbi (Cysteamine Bitartrate)

What Is Procysbi and What Is It Used For?

Quick Answer: Procysbi contains the active substance cysteamine (also known as mercaptamine) and is used to treat nephropathic cystinosis in children and adults. It works by reducing the abnormal accumulation of the amino acid cystine inside cells, thereby protecting organs from progressive damage.

Nephropathic cystinosis is a rare autosomal recessive lysosomal storage disorder that affects approximately 1 in 100,000 to 200,000 live births worldwide. The condition is caused by mutations in the CTNS gene, which encodes the protein cystinosin — a lysosomal membrane transporter responsible for moving cystine out of lysosomes. When this transporter is defective, cystine accumulates within the lysosomes of virtually every cell in the body, forming crystals that cause progressive cellular and tissue damage.

The kidneys are typically the first organs affected in nephropathic cystinosis, with symptoms often appearing in the first year of life. Children may develop renal Fanconi syndrome, characterized by excessive loss of glucose, amino acids, phosphate, and other electrolytes in the urine. Without treatment, the disease progresses to end-stage renal failure, usually by the age of 10. However, cystine accumulation also damages the eyes (causing photophobia and corneal crystals), muscles (leading to weakness and wasting), pancreas (potentially causing diabetes), thyroid, liver, and central nervous system.

Procysbi is a cystine-depleting agent that works by entering the lysosomes and reacting with cystine through a thiol-disulfide interchange reaction. This converts cystine into the amino acid cysteine and a cysteine-cysteamine mixed disulfide compound, both of which can exit the lysosome through alternative transport mechanisms. By reducing intracellular cystine levels, Procysbi helps prevent the formation of damaging cystine crystals and slows the progression of organ damage.

What makes Procysbi unique compared to earlier cysteamine formulations is its delayed-release technology. The enteric-coated granules within each capsule are designed to resist dissolution in the stomach and release cysteamine in the small intestine. This allows for twice-daily dosing (every 12 hours) rather than the four-times-daily dosing (every 6 hours) required with immediate-release cysteamine products. Clinical studies have demonstrated that Procysbi maintains comparable white blood cell cystine levels while significantly reducing dosing burden, which is crucial for lifelong treatment adherence.

What Should You Know Before Taking Procysbi?

Quick Answer: Do not take Procysbi if you are allergic to cysteamine, penicillamine, or if you are breastfeeding. Important precautions include monitoring for skin lesions, gastrointestinal complications, neurological symptoms, and liver function changes during treatment.

Contraindications

Procysbi is contraindicated in several specific situations that must be carefully evaluated before starting treatment. You should not take Procysbi if:

• Allergy to cysteamine (mercaptamine) or any of the other ingredients in the medicine (see the Contents section for a full list).
• Allergy to penicillamine — although penicillamine is a different medication (used for Wilson's disease, not related to penicillin antibiotics), there is a structural relationship with cysteamine that may lead to cross-reactivity.
• Breastfeeding — cysteamine may pass into breast milk and could harm the nursing infant. Women who need to take Procysbi should not breastfeed.

Warnings and Precautions

Several important warnings apply to patients taking Procysbi. Your doctor will monitor you for these potential complications throughout treatment:

Gastrointestinal complications: Ulcers and bleeding in the stomach and intestines have been reported in patients receiving cysteamine. Common gastrointestinal symptoms include nausea, vomiting, loss of appetite, and abdominal pain. If you experience unusual stomach symptoms, black or bloody stools, or vomit blood, contact your doctor immediately. The dose may need to be adjusted or temporarily suspended.

Neurological symptoms: Cysteamine treatment may cause seizures, excessive drowsiness, depression, and encephalopathy (brain dysfunction). If you experience any of these symptoms, inform your doctor promptly so they can adjust your dose accordingly. These effects are typically dose-related and may resolve with dosage reduction.

Liver function and blood counts: Abnormal liver function tests and reduced white blood cell counts (leukopenia) can occur during cysteamine therapy. Your doctor will perform regular blood tests to monitor liver enzymes and complete blood counts throughout your treatment.

Benign intracranial hypertension (pseudotumor cerebri): Increased pressure within the skull has been reported with cysteamine use. Symptoms may include ringing or buzzing in the ears, dizziness, double vision, blurred vision, decreased vision, pain behind the eyes, or pain with eye movements. Regular eye examinations are recommended to detect this condition early, as prompt treatment can help prevent permanent vision loss.

Children under 6 years: Whole capsules should not be given to children under 6 years of age due to the risk of choking. Instead, the capsule can be opened and the contents sprinkled on soft food or mixed into acidic juice according to specific administration instructions.

Pregnancy and Breastfeeding

Procysbi has important restrictions regarding use during pregnancy and breastfeeding. The safety of cysteamine during human pregnancy has not been established, and animal studies have shown potential for fetal harm.

Pregnancy: You should not use Procysbi if you are pregnant, particularly during the first trimester. Before starting treatment, a negative pregnancy test is required. Women of childbearing potential must use reliable contraception throughout the treatment period. If you are planning to become pregnant or discover that you are pregnant, contact your doctor immediately. Treatment may need to be discontinued because continued use could be harmful to the unborn child.

Breastfeeding: Procysbi must not be used during breastfeeding. Cysteamine may be excreted in breast milk, and the potential risks to the nursing infant are unknown. If you are currently breastfeeding, you should either stop breastfeeding before starting Procysbi or discuss alternative treatment options with your doctor.

Driving and operating machinery: Procysbi may cause drowsiness, particularly when starting treatment. Avoid driving, operating machinery, or engaging in hazardous activities until you know how the medicine affects you.

How Does Procysbi Interact with Other Drugs?

Quick Answer: Procysbi can interact with sodium bicarbonate (which should be taken at least 1 hour apart), proton pump inhibitors, and foods that reduce stomach acidity. Avoid high-fat or high-protein meals and dairy products within 1 hour before and after taking Procysbi.

Although formal drug interaction studies with Procysbi are limited, several important interactions have been identified based on the pharmacological properties of cysteamine and the delayed-release formulation. It is essential to inform your doctor about all medications you are currently taking, have recently taken, or plan to take.

Important Drug Interactions

Food and Drink Interactions

The timing of food intake relative to Procysbi dosing is important for optimal drug absorption. You should avoid meals rich in fat or protein, as well as dairy products such as milk and yoghurt, for at least 1 hour before and 1 hour after taking Procysbi. These foods can reduce stomach acidity, which may affect how the delayed-release coating dissolves and releases the medication.

If it is not possible to avoid food entirely during the 1-hour windows before and after dosing, you may eat a small amount (approximately 100 grams) of food, preferably carbohydrates such as bread, pasta, or fruit. The capsules should be taken with an acidic drink (such as orange juice or another acidic fruit juice) or plain water. Acidic beverages may help maintain the appropriate pH environment in the stomach and intestines for optimal drug release.

Electrolyte Supplements

Your doctor may prescribe electrolyte supplements to replace important salts lost through the kidneys due to cystinosis (e.g., potassium, phosphate, sodium bicarbonate, carnitine, and vitamin D). It is important to take these supplements exactly as directed. If you miss several doses of supplements or feel weak or lethargic, contact your doctor for guidance. Note that sodium bicarbonate specifically should be separated from Procysbi by at least 1 hour.

What Is the Correct Dosage of Procysbi?

Quick Answer: Procysbi is dosed based on body surface area, with a target maintenance dose of 1.3 g/m²/day divided into two equal doses taken every 12 hours. The maximum recommended total daily dose should not exceed 1.95 g/m²/day. Dosing is individualized based on regular white blood cell cystine level monitoring.

Always take Procysbi exactly as your doctor or pharmacist has instructed. The dose is calculated based on your body surface area (measured in square meters, m²), which takes into account both your weight and height. Treatment is lifelong and must be continued as directed by your doctor.

Adults and Children

Your doctor will determine the optimal starting dose and may gradually increase it based on your white blood cell (WBC) cystine levels. Regular blood tests are essential for monitoring treatment effectiveness. These tests should be performed 12.5 hours after your evening dose — that is, 30 minutes after taking your next morning dose.

Administration for Children Under 6 Years

Children under 6 years of age should not swallow whole capsules due to the risk of choking. Instead, the capsule can be opened and the contents (granules) administered in one of several ways:

• Sprinkled on food: Open the capsule and sprinkle the granules onto approximately 100 grams of soft food such as applesauce or jam. Gently stir to mix, then eat the entire mixture immediately. Follow with 250 mL of acidic juice or water. If not consumed immediately, the mixture may be refrigerated (2–8°C) for up to 2 hours.
• Mixed in juice: Open the capsule and sprinkle the granules into approximately 100–150 mL of acidic juice or water. Gently mix for 5 minutes, then drink the entire mixture. The juice mixture must be consumed within 30 minutes if refrigerated.
• Via dosing syringe: The juice mixture can also be drawn up in a syringe and administered directly into the mouth.

Administration via Feeding Tube

For patients with feeding tubes (gastrostomy, nasogastric, or gastrostomy-jejunostomy tubes), the capsule contents can be mixed with applesauce or jam and administered via catheter-tip syringe. A maximum volume of 60 mL per syringe is recommended. Flush the tube with 5 mL of water before administration and 10 mL of juice or water afterward to ensure complete delivery. Administer at a rate of approximately 10 mL every 10 seconds to prevent tube blockage.

Missed Dose

If you miss a dose of Procysbi, take it as soon as you remember. However, if there are fewer than 4 hours remaining until your next scheduled dose, skip the missed dose and return to your regular dosing schedule. Never take a double dose to make up for a forgotten dose.

Overdose

Monitoring Requirements

Regular monitoring is essential for safe and effective Procysbi treatment. Your doctor will schedule the following tests:

• White blood cell cystine levels: The primary measure of treatment effectiveness. Blood should be drawn 12.5 hours after the evening dose (30 minutes after the morning dose). Target levels are typically below 1 nmol half-cystine per mg protein.
• Blood cysteamine concentration: May be measured to help guide dosing.
• Complete blood count: To monitor for leukopenia (low white blood cells).
• Liver function tests: To detect potential hepatotoxicity.
• Kidney function tests: To monitor disease progression.
• Electrolyte levels: To adjust supplement doses for lost salts.
• Eye examinations: To monitor for benign intracranial hypertension (papilledema) and corneal crystals.
• Skin and bone assessments: To detect dermatologic or skeletal complications of treatment.

What Are the Side Effects of Procysbi?

Quick Answer: The most common side effects of Procysbi include nausea, vomiting, decreased appetite, diarrhea, fever, and drowsiness. Serious but less common side effects include severe skin lesions, gastrointestinal ulcers, seizures, and benign intracranial hypertension. Seek immediate medical attention for signs of allergic reaction.

Like all medicines, Procysbi can cause side effects, although not everyone experiences them. The frequency and severity of side effects can vary between individuals and are often dose-related. Many gastrointestinal side effects tend to improve over time as the body adjusts to the medication. Your doctor may adjust your dose if side effects become troublesome.

Managing Common Side Effects

Body and breath odor: An unpleasant sulfurous odor is one of the most socially challenging side effects of cysteamine therapy. This is caused by the sulfur-containing nature of the drug. While the odor cannot be entirely eliminated, some patients find that taking the medication with acidic juice and maintaining good hygiene helps reduce the intensity. Discuss any concerns with your doctor, but do not reduce your dose without medical guidance.

Gastrointestinal symptoms: Nausea, vomiting, and abdominal discomfort are common, especially early in treatment. Taking Procysbi on a relatively empty stomach (as recommended) may initially worsen these symptoms, but they often improve over time. Your doctor may start with a lower dose and gradually increase it to help minimize gastrointestinal effects. If vomiting occurs within 20 minutes of taking a dose, you should consult your doctor about whether to repeat the dose.

Drowsiness: This effect is particularly common when starting treatment or after dose increases. Avoid driving or operating heavy machinery until you know how Procysbi affects you. If drowsiness is severe or persistent, your doctor may adjust the dose.

How Should You Store Procysbi?

Quick Answer: Store Procysbi in a refrigerator (2–8°C / 36–46°F). Once opened, the bottle can be stored at room temperature up to 25°C (77°F) for a maximum of 30 days. Keep the container tightly closed and protect from light and moisture.

Proper storage of Procysbi is essential to maintain the medication's effectiveness and safety. The delayed-release coating is sensitive to environmental conditions, making correct storage particularly important.

• Unopened bottles: Store in a refrigerator at 2–8°C (36–46°F). Do not freeze.
• Opened bottles: May be stored at room temperature up to 25°C (77°F). Keep the container tightly closed.
• 30-day limit: Do not use the medicine if the foil seal has been broken for more than 30 days. Discard the opened bottle and use a new one.
• Light protection: Keep the medicine protected from light at all times.
• Moisture protection: The bottle contains plastic desiccant containers to absorb moisture. Leave these containers inside the bottle throughout the entire period of use. They may be discarded together with the bottle when finished.
• Keep out of reach of children: Store the medicine where children cannot see or reach it.
• Expiry date: Check the expiration date on the carton and bottle label (marked EXP). Do not use after the last day of the indicated month.

Do not dispose of medications via the sink or toilet. Ask your pharmacist how to properly dispose of medicines that are no longer needed. Proper disposal helps protect the environment.

What Does Procysbi Contain?

Quick Answer: The active ingredient is cysteamine (as mercaptamine bitartrate), available in 25 mg and 75 mg delayed-release hard capsules. The capsules contain enteric-coated granules and are distinguishable by size and color intensity.

Active Ingredient

The active substance is cysteamine, present as mercaptamine bitartrate:

• Procysbi 25 mg: Each delayed-release hard capsule contains 25 mg cysteamine
• Procysbi 75 mg: Each delayed-release hard capsule contains 75 mg cysteamine

Other Ingredients (Excipients)

Capsule contents: Microcrystalline cellulose, methacrylic acid-ethyl acrylate copolymer (1:1), hypromellose, talc, triethyl citrate, sodium lauryl sulfate.

Capsule shell: Gelatin, titanium dioxide (E171), indigo carmine (E132).

Printing ink: Shellac, povidone (K-17), titanium dioxide (E171).

Appearance and Pack Sizes

Both presentations come in white plastic bottles with child-resistant caps and foil seals. The desiccant containers inside the bottles provide additional protection against moisture and air. Leave these containers in the bottle during the entire usage period.

Marketing Authorization Holder and Manufacturer

Marketing authorization holder: Chiesi Farmaceutici S.p.A., Via Palermo 26/A, 43122 Parma, Italy.

Manufacturer: Chiesi Farmaceutici S.p.A., Via San Leonardo 96, 43122 Parma, Italy.

For additional information about this medicine, contact the local representative of the marketing authorization holder in your country, or visit the EMA website for the full European Public Assessment Report (EPAR).

References

1. European Medicines Agency (EMA). Procysbi – European Public Assessment Report (EPAR). Product information last updated 2025. Available at: www.ema.europa.eu
2. 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 International. 2016;89(6):1192-1203.
3. Ariceta G, Giordano V, Santos F. Effects of long-term cysteamine treatment in patients with cystinosis. Pediatric Nephrology. 2019;34(4):571-578.
4. Dohil R, Fidler M, Gangoiti JA, et al. Twice-daily cysteamine bitartrate therapy for children with cystinosis. The Journal of Pediatrics. 2010;156(1):71-75.
5. Nesterova G, Gahl WA. Nephropathic cystinosis: late complications of a multisystemic disease. Pediatric Nephrology. 2008;23(6):863-878.
6. World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List (2023). Geneva: World Health Organization; 2023.
7. Elmonem MA, Veys KR, Soliman NA, et al. Cystinosis: a review. Orphanet Journal of Rare Diseases. 2016;11:47.
8. U.S. Food and Drug Administration (FDA). Procysbi – Full Prescribing Information. Available at: www.fda.gov
9. British National Formulary (BNF). Mercaptamine (Cysteamine). National Institute for Health and Care Excellence. Available at: bnf.nice.org.uk

Editorial Team

This article has been written and reviewed by the iMedic Medical Editorial Team, comprising licensed physicians specializing in clinical pharmacology, nephrology, and rare metabolic diseases. Our editorial process follows international standards for medical content accuracy, including adherence to EMA, FDA, and WHO guidelines.