Definition & Mechanism
- Glucarpidase is a recombinant bacterial enzyme (carboxypeptidase G2) used as a rescue agent to rapidly lower toxic plasma methotrexate levels in patients with impaired renal function.
- It works by hydrolyzing methotrexate into inactive metabolites (glutamate and DAMPA), providing a non-renal pathway for methotrexate elimination.
Indication
- Indicated for patients experiencing delayed methotrexate clearance due to renal dysfunction, especially after high-dose methotrexate therapy for cancers such as leukemia, lymphoma, and osteosarcoma.
Administration
- Given as a single intravenous injection (50 units/kg) over 5 minutes.
- Should be used in conjunction with leucovorin, but leucovorin must be administered at least 2 hours before or after glucarpidase to avoid inactivation.
Key Clinical Points
- Rapid Action: Reduces plasma methotrexate levels by >95% within 15 minutes in most patients.
- Not for Routine Use: Only for patients with toxic methotrexate levels and impaired renal clearance; not for those with normal or mildly impaired renal function.
- Monitoring: Methotrexate assays may be unreliable after glucarpidase due to cross-reactivity with DAMPA; use chromatographic methods for accurate measurement.
- Adverse Effects: Generally well tolerated; hypersensitivity reactions are rare.
- No Dose Adjustment: Not required for renal or hepatic impairment.
Summary Table
| Aspect | Key Point |
|---|---|
| Mechanism | Enzymatic hydrolysis of methotrexate to inactive metabolites |
| Indication | Toxic methotrexate levels with renal dysfunction |
| Administration | IV injection, 50 units/kg, single dose |
| Use with Leucovorin | Separate by at least 2 hours |
| Monitoring | Use chromatographic assays for methotrexate post-glucarpidase |
| Major Toxicities | Rare; hypersensitivity possible |
Glucarpidase is a critical rescue agent for oncology patients with life-threatening methotrexate toxicity and renal impairment, enabling rapid drug clearance and reducing the risk of severe toxicity.
Comparison for Oncology Pharmacy Practice
| Feature | Calcium Folinate | Glucarpidase |
|---|---|---|
| Primary Function | Cellular folate rescue | Plasma MTX elimination |
| Lowers serum MTX? | ❌ No | ✅ Yes (rapidly) |
| Works intracellularly? | ✅ Yes | ❌ No |
| Role in routine HD-MTX? | Standard of care | Not routine |
| Role in MTX-induced AKI? | Supportive but insufficient alone | Definitive rescue |
| Timing sensitivity | Critical | Emergency use in delayed clearance |
| Cost | Low | Extremely high |
| Impact on MTX efficacy | Can reduce if overdosed | No direct effect on tumor intracellular MTX |