rasburicase

the uric acid eraser

A recombinant urate oxidase enzyme. It converts existing uric acid (insoluble/nephrotoxic) into allantoin (highly soluble/excretable).

• Mechanism: Enzymatic degradation of uric acid.
• Indication: Tumour Lysis Syndrome (TLS).
  • Hyperuricaemia $>475$ µmol/L.
  • High-risk prophylaxis (Burkitt’s, ALL with high WBC).

dosing & practicalities

• Dose: Often fixed dose (e.g., 3 mg or 4.5 mg or 6 mg flat dose) is effective. Weight-based dosing (0.2 mg/kg) often excessive/expensive.
• Onset: Dramatic drop in uric acid within 4 hours.

contraindications & safety

• G6PD Deficiency:
  • Mechanism: Degradation of uric acid produces Hydrogen Peroxide ($H_2{O}_2$). In G6PD deficiency, this causes massive haemolysis and methaemoglobinaemia.
  • Screening: Recommended for high-risk ethnic groups before use if time permits.
• Sample Handling (CRITICAL):
  • Blood samples for Uric Acid must be transported on ICE. Rasburicase continues to work ex vivo in the tube, causing a falsely low result.