Fasturtec (Rasburicase)

What Is Fasturtec and What Is It Used For?

Fasturtec (rasburicase) is an intravenous enzyme therapy used to treat and prevent hyperuricaemia – dangerously high levels of uric acid in the blood – in patients with haematological cancers who are about to start or are already receiving chemotherapy. It is approved for use in adults, children, and adolescents from birth to 17 years of age.

When patients with blood cancers such as leukaemia, lymphoma, or other haematological malignancies undergo chemotherapy, large numbers of cancer cells are destroyed simultaneously. This rapid cell destruction releases enormous quantities of intracellular contents into the bloodstream, including purines – the building blocks of DNA. The body metabolises these purines into uric acid. Under normal circumstances, the kidneys can handle moderate levels of uric acid, but the sudden flood caused by chemotherapy can overwhelm the renal system, leading to a dangerous condition known as tumour lysis syndrome (TLS).

Tumour lysis syndrome is a potentially life-threatening oncological emergency characterised by hyperuricaemia (high uric acid), hyperkalaemia (high potassium), hyperphosphataemia (high phosphate), and hypocalcaemia (low calcium). When uric acid levels rise dramatically, uric acid crystals can precipitate in the renal tubules, causing acute kidney injury or renal failure. Without prompt intervention, TLS can lead to cardiac arrhythmias, seizures, multi-organ failure, and death. The American Society of Clinical Oncology (ASCO) and the European Society for Medical Oncology (ESMO) both classify TLS as a medical emergency requiring immediate management.

Fasturtec contains rasburicase, a recombinant form of the enzyme urate oxidase (uricase), produced by a genetically modified strain of the yeast Saccharomyces cerevisiae. Urate oxidase is an enzyme found naturally in most mammals but is absent in humans due to a mutation in the gene that occurred during primate evolution. This enzyme catalyses the oxidation of uric acid into allantoin, a metabolite that is approximately five to ten times more water-soluble than uric acid and is readily excreted by the kidneys. By providing this missing enzyme, Fasturtec enables the body to rapidly break down and eliminate excess uric acid.

Unlike allopurinol, which works by inhibiting xanthine oxidase to prevent the formation of new uric acid, rasburicase actively degrades existing uric acid that has already accumulated in the blood. This fundamental difference in mechanism of action explains why Fasturtec works dramatically faster – significant reductions in plasma uric acid are typically observed within 4 hours of the first dose, compared to days with allopurinol. For patients at high risk of TLS, this rapid onset of action can be the difference between preserving kidney function and developing irreversible renal damage.

What Should You Know Before Receiving Fasturtec?

Before receiving Fasturtec, your doctor must ensure you do not have G6PD deficiency, a history of haemolytic anaemia, or known allergy to rasburicase or other uricases. These are absolute contraindications. Patients should also inform their healthcare team about all other medications, allergies, pregnancy or breastfeeding status.

Fasturtec is a powerful biologic agent that, while highly effective at lowering uric acid, carries significant risks in certain patient populations. Your treating physician and healthcare team will conduct a thorough assessment before initiating treatment. It is critically important that you provide complete information about your medical history, as some contraindications to Fasturtec can lead to life-threatening complications if the medication is administered.

Contraindications

You must not receive Fasturtec if any of the following apply:

• Allergy to rasburicase, other uricases, or any excipient – Fasturtec is a protein-based drug and can trigger severe allergic reactions including anaphylaxis. If you have previously experienced an allergic reaction to any uricase enzyme, you must not receive this medication
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency – This is the most critical contraindication. Rasburicase generates hydrogen peroxide as a byproduct of the enzymatic conversion of uric acid to allantoin. In patients with G6PD deficiency, red blood cells cannot adequately neutralise this oxidative stress, leading to potentially fatal haemolytic anaemia (destruction of red blood cells). G6PD deficiency is particularly prevalent among individuals of African, Mediterranean, and Southeast Asian descent
• Other metabolic disorders causing haemolytic anaemia – Any cellular metabolic disorder that impairs the ability of red blood cells to handle oxidative stress is a contraindication to Fasturtec
• History of haemolytic anaemia or methemoglobinaemia – Patients who have experienced these conditions from any cause should not receive rasburicase

Warnings and Precautions

Talk to your doctor or nurse before receiving Fasturtec if you have any kind of allergy. Inform your doctor if you have ever had an allergic reaction to any medication, as Fasturtec can cause allergic-type reactions including severe anaphylaxis. These reactions can occur with any dose, including the first dose, and may be life-threatening.

Tell your healthcare team immediately if you notice any of the following symptoms during or after the infusion, as these may be early signs of a serious allergic reaction requiring immediate medical intervention:

• Swelling of the face, lips, tongue, or throat
• Coughing or wheezing
• Difficulty breathing or swallowing
• Skin rash, itching, or hives (urticaria)
• Feeling dizzy, lightheaded, or faint
• Chest tightness or pain

If an allergic reaction occurs, your doctor will immediately and permanently discontinue Fasturtec and provide appropriate emergency treatment. It is not currently known whether the risk of allergic reaction increases with repeated courses of treatment, so particular vigilance is warranted if retreatment is considered.

If signs of a blood disorder develop – such as haemolysis (abnormal breakdown of red blood cells) or methemoglobinaemia (abnormal levels of blood pigment resulting in a brownish discolouration of blood and potential tissue hypoxia) – your doctor will immediately and permanently stop treatment with Fasturtec. These haematological adverse effects require urgent medical management.

Pregnancy and Breastfeeding

The safety of Fasturtec during pregnancy has not been established. There are no adequate and well-controlled studies in pregnant women. Animal reproduction studies have not been conducted with rasburicase. If you are pregnant, think you may be pregnant, or are planning to become pregnant, you must inform your doctor before receiving Fasturtec. Your doctor will carefully weigh the potential benefits of treatment against the possible risks to the unborn child.

It is not known whether rasburicase is excreted in human breast milk. Because many drugs are excreted in breast milk and because of the potential for adverse reactions in the nursing infant, a decision should be made whether to discontinue breastfeeding or to withhold the drug, taking into account the importance of the treatment to the mother. Discuss this with your healthcare provider.

Driving and Operating Machinery

There is no specific information available regarding the effect of Fasturtec on the ability to drive or use machines. However, given that Fasturtec is administered in a hospital or clinic setting to patients undergoing cancer treatment, driving is unlikely to be a primary concern during the treatment period. If you experience any side effects such as dizziness or fatigue, do not drive or operate machinery until these symptoms have resolved.

Sodium Content

Fasturtec contains up to 10.5 mg of sodium (the main component of cooking/table salt) per vial. This is equivalent to approximately 0.53% of the recommended maximum daily intake of sodium for an adult (2 g/day as recommended by the WHO). Healthcare professionals should take this into account for patients on sodium-restricted diets, particularly if multiple vials are required per dose based on the patient's body weight.

How Does Fasturtec Interact with Other Drugs?

No formal drug interaction studies have been conducted with Fasturtec. However, because it is an enzyme that acts on uric acid rather than being metabolised by liver enzymes, pharmacokinetic drug interactions are considered unlikely. The main interaction concern is with other uric acid-lowering agents and laboratory interference with uric acid measurements.

Rasburicase is a recombinant enzyme protein that works by directly converting uric acid to allantoin in the blood. Unlike most small-molecule drugs, it does not undergo hepatic metabolism through cytochrome P450 enzymes or other liver-based metabolic pathways. As a result, pharmacokinetic interactions with co-administered medications are not expected. Nevertheless, patients receiving Fasturtec are typically undergoing complex chemotherapy regimens with multiple concurrent medications, so healthcare providers should always be informed of all medicines being taken.

Inform your doctor or pharmacist if you are taking, have recently taken, or might take any other medicines, including over-the-counter preparations and herbal supplements. While direct drug-drug interactions are not well documented for rasburicase, there are several clinically important considerations when Fasturtec is used alongside other medications:

What Is the Correct Dosage of Fasturtec?

The recommended dose of Fasturtec is 0.20 mg per kilogram of body weight per day, administered as a 30-minute intravenous infusion once daily for up to 7 days. The dose is the same for adults, children, and adolescents. Treatment duration is determined by the physician based on uric acid monitoring and clinical response.

Fasturtec is always administered in a hospital or clinical setting by trained healthcare professionals. It is never self-administered. The medication is given before the start of chemotherapy or during the initial phase of chemotherapy treatment, when the risk of tumour lysis syndrome and hyperuricaemia is highest. Your medical team will calculate the precise dose based on your body weight and prepare the infusion according to strict aseptic protocols.

Adults

Children and Adolescents (0–17 years)

Elderly Patients

No specific dose adjustment is required for elderly patients. The standard dose of 0.20 mg/kg per day applies regardless of age. However, elderly patients may have a higher prevalence of comorbidities and reduced organ function, warranting closer monitoring during treatment. Renal function and fluid balance should be carefully assessed throughout the treatment course.

Treatment Duration and Monitoring

During treatment with Fasturtec, your doctor will take regular blood tests to monitor plasma uric acid levels and determine how long treatment should continue. In many cases, treatment courses are shorter than the maximum 7 days, as uric acid levels may normalise rapidly. Your doctor may also monitor your blood for signs of haemolysis (destruction of red blood cells) or methemoglobinaemia, particularly during the first few days of treatment.

The decision to continue or discontinue treatment is based on several factors: the plasma uric acid concentration, the patient's clinical condition, the type and intensity of the chemotherapy regimen, and whether the peak period of tumour cell destruction has passed. In practice, many patients receive Fasturtec for 3 to 5 days, though the full 7-day course may be necessary for patients with very high tumour burden or persistent hyperuricaemia.

Overdose

If an overdose occurs, the doctor will carefully monitor the patient for any effects on red blood cells, including haemolysis and methemoglobinaemia, and provide appropriate supportive treatment for any symptoms that develop. There is no specific antidote for rasburicase overdose. At higher-than-recommended doses, more pronounced uric acid lowering is expected, but the primary clinical concern is the potential for increased oxidative stress on red blood cells.

What Are the Side Effects of Fasturtec?

Like all medicines, Fasturtec can cause side effects, although not everybody gets them. The most common side effects are gastrointestinal symptoms (diarrhoea, vomiting, nausea), headache, and fever. Serious side effects include allergic reactions (including anaphylaxis), haemolytic anaemia, and methemoglobinaemia. Since Fasturtec is given alongside chemotherapy, it can be difficult to distinguish drug-specific side effects from those caused by the underlying cancer or concurrent treatments.

It is important to understand that patients receiving Fasturtec are simultaneously undergoing intensive chemotherapy and often have serious underlying haematological malignancies. Many of the symptoms reported during treatment may be caused by the cancer itself, the chemotherapy drugs, or the complications of tumour lysis syndrome rather than by Fasturtec specifically. Your healthcare team will carefully monitor you throughout treatment and can help distinguish between expected treatment effects and potential drug-related adverse events.

If you suddenly notice any of the following signs, tell your doctor, nurse, or pharmacist immediately as these may indicate a serious allergic reaction:

• Swelling of the face, lips, tongue, or other body parts
• Shortness of breath, wheezing, or breathing difficulties
• Rash, itching, or hives

If you notice any of the listed side effects, or any other unusual symptoms during or after your Fasturtec infusion, inform your doctor, nurse, or pharmacist. Reporting suspected adverse reactions after the drug has been authorised is important, as it enables ongoing monitoring of the medicine's benefit-risk balance.

How Should Fasturtec Be Stored?

Fasturtec must be stored in a refrigerator at 2°C to 8°C. It must not be frozen. It should be kept in the original packaging to protect from light. Once reconstituted, the solution should be used immediately. Any unused solution must be discarded.

As a hospital-use medication, Fasturtec storage is managed by the pharmacy department. However, understanding storage requirements is important for ensuring the medication's efficacy and safety:

• Temperature: Store in a refrigerator between 2°C and 8°C (36°F to 46°F)
• Freezing: Do not freeze under any circumstances
• Light protection: Keep in the original packaging to protect from light, as rasburicase is a light-sensitive protein
• Expiry date: Do not use after the expiry date stated on the carton (EXP). The expiry date refers to the last day of the stated month
• After reconstitution: The reconstituted and diluted solution does not contain preservatives and should be infused immediately. Do not store reconstituted solution for later use
• Visual inspection: Do not use this medicine if you notice discolouration or particles in the reconstituted solution. Only a clear, colourless solution should be used

Keep all medicines out of the sight and reach of children. The reconstituted solution is for single use only – any remaining solution after the infusion must be disposed of according to local hospital pharmaceutical waste protocols.

What Does Fasturtec Contain?

The active substance is rasburicase at a concentration of 1.5 mg/ml after reconstitution. It is produced by a genetically modified yeast (Saccharomyces cerevisiae). The powder and solvent also contain several inactive ingredients necessary for stability, pH buffering, and reconstitution.

Active Substance

Rasburicase 1.5 mg/ml (after reconstitution). Rasburicase is a recombinant urate oxidase enzyme manufactured using a genetically modified strain of Saccharomyces cerevisiae (baker's yeast). It is a tetrameric protein with a molecular weight of approximately 135 kDa.

Inactive Ingredients (Excipients)

In the powder:

• Alanine (amino acid stabiliser)
• Mannitol (bulking agent)
• Disodium phosphate dodecahydrate (pH buffer)
• Disodium phosphate dihydrate (pH buffer)
• Sodium dihydrogen phosphate dihydrate (pH buffer)

In the solvent:

• Poloxamer 188 (surfactant/stabiliser)
• Water for injections

Presentation and Pack Sizes

Fasturtec is supplied as a powder for concentrate for solution for infusion together with a solvent. The powder appears as white to off-white crushed or whole pellets. The solvent is a clear, colourless liquid.

• 1.5 mg pack: Contains 3 vials of 1.5 mg rasburicase powder and 3 ampoules of 1 ml solvent. The powder is supplied in 2 or 3 ml clear glass vials with rubber stoppers.
• 7.5 mg pack: Contains 1 vial of 7.5 mg rasburicase powder and 1 ampoule of 5 ml solvent. The powder is supplied in a 10 ml clear glass vial with a rubber stopper.

Not all pack sizes may be marketed in all countries.

Reconstitution and Administration (For Healthcare Professionals)

Fasturtec must be reconstituted with the entire volume of the supplied solvent (1.5 mg vial with 1 ml solvent; 7.5 mg vial with 5 ml solvent). The reconstituted solution has a concentration of 1.5 mg/ml. The vial should be gently swirled – do not shake – and visually inspected before use. Only a clear, colourless, particle-free solution should be used.

The required volume of reconstituted solution (based on the patient's body weight at 0.20 mg/kg) is then further diluted with 0.9% sodium chloride solution to a total volume of 50 ml. The final infusion solution should be administered immediately over 30 minutes. The reconstituted solution does not contain preservatives, so aseptic technique must be maintained throughout preparation.

How Does Fasturtec Work in the Body?

Rasburicase catalyses the enzymatic oxidation of uric acid into allantoin, carbon dioxide, and hydrogen peroxide. Allantoin is 5–10 times more water-soluble than uric acid and is easily excreted by the kidneys. This enzymatic degradation of existing uric acid provides rapid and profound uric acid lowering that is not achievable with xanthine oxidase inhibitors alone.

To understand how Fasturtec works, it is helpful to understand the biochemistry of uric acid metabolism. In the human body, purines (adenine and guanine – building blocks of DNA and RNA) are broken down through a metabolic pathway that ends with the production of uric acid. In most other mammals, an enzyme called urate oxidase (uricase) further converts uric acid into allantoin. However, during human evolution, the gene encoding urate oxidase became non-functional through a series of mutations. This means that humans lack the ability to further break down uric acid, making it the end product of purine metabolism. This evolutionary quirk explains why humans are susceptible to conditions caused by excess uric acid, including gout and the hyperuricaemia associated with tumour lysis syndrome.

Rasburicase provides the missing enzymatic step. When administered intravenously, it circulates in the bloodstream and catalyses the following reaction:

The clinical impact of this enzymatic activity is dramatic. Plasma uric acid levels begin to fall within minutes of starting the infusion, with clinically significant reductions achieved within 4 hours of the first dose. In clinical trials, rasburicase reduced plasma uric acid levels by an average of 86% within 4 hours, compared to a 12% reduction with allopurinol over the same timeframe. This rapid onset is critical in the management of TLS, where every hour of persistent hyperuricaemia increases the risk of renal damage.

The terminal elimination half-life of rasburicase is approximately 18 hours, supporting once-daily dosing. Unlike small-molecule drugs, rasburicase is eliminated through proteolytic degradation (broken down into amino acids) rather than hepatic or renal excretion, which means dose adjustments are not required for patients with liver or kidney impairment.

It is important to note that the hydrogen peroxide generated by the enzymatic reaction is normally neutralised by the glutathione-dependent antioxidant defence system in red blood cells. In patients with G6PD deficiency, the regeneration of reduced glutathione is impaired, leaving red blood cells vulnerable to oxidative damage. This is the biochemical basis for the critical contraindication of Fasturtec in G6PD-deficient patients and the risk of haemolytic anaemia and methemoglobinaemia.

Frequently Asked Questions