Glucarpidase (Monograph)

Brand name: Voraxaze
Drug class: Antidotes
Chemical name: Recombinant glutamate carboxypeptidase (carboxypeptidase G2)
Molecular formula: C₁₉₅₀H₃₁₅₇N₅₄₃O₅₉₉S₇
CAS number: 9074-87-7

Introduction

Antidote for methotrexate toxicity; recombinant bacterial enzyme.

Uses for Glucarpidase

Methotrexate Toxicity

Adjunct to leucovorin rescue for the treatment of toxic plasma methotrexate concentrations (>0.454 mcg/mL [1 µmol/L]) in patients with delayed methotrexate clearance due to renal impairment (designated an orphan drug by FDA for this use ).

Because of potential for subtherapeutic methotrexate concentrations, do not use in patients who exhibit the expected clearance of methotrexate (plasma methotrexate concentrations within 2 standard deviations of the mean methotrexate excretion curve specific for the methotrexate dose administered) or in those with normal or mildly impaired renal function.

Provides an alternative, nonrenal route for methotrexate elimination (in patients with delayed methotrexate clearance due to renal impairment) by converting circulating methotrexate to inactive metabolites that are primarily eliminated hepatically.

Glucarpidase Dosage and Administration

General

Methotrexate Toxicity

• Use only in patients who exhibit delayed methotrexate clearance (plasma methotrexate concentrations >2 standard deviations greater than the mean methotrexate excretion curve specific for the methotrexate dose administered) due to renal impairment. Early recognition of delayed methotrexate clearance and renal impairment (i.e., an increase in S_cr and/or oliguria) and urgent intervention are essential to prevent development of severe methotrexate-induced toxicities.

• Use in conjunction with leucovorin rescue and supportive measures (i.e., IV hydration, urinary alkalinization with sodium bicarbonate). Because the pharmacokinetics of leucovorin and levoleucovorin are similar, manufacturer of glucarpidase states may substitute levoleucovorin for leucovorin.

Administration

IV Administration

Administer by direct IV injection; flush IV line before and after administration of drug.

Reconstitution

Use strict aseptic technique since drug product contains no preservative.

Add 1 mL of 0.9% sodium chloride injection to vial containing 1000 units of glucarpidase. Gently roll and tilt vial to ensure dissolution; do not shake.

Rate of Administration

Administer by direct IV injection over 5 minutes.

Dosage

Dosage expressed in terms of units; a unit of activity is the quantity of enzyme needed to catalyze hydrolysis of 1 µmol/L of methotrexate per minute at 37°C.

Pediatric Patients

Methotrexate Toxicity

IV

50 units/kg as a single dose. Second dose not shown to produce further reduction in methotrexate concentrations.

Continue leucovorin (or levoleucovorin ) rescue. (See Specific Drugs under Interactions.) During first 48 hours after glucarpidase administration, administer leucovorin (or levoleucovorin) at same dosage administered prior to glucarpidase; beyond 48 hours, base dosage on methotrexate concentration. Continue leucovorin (or levoleucovorin) rescue until methotrexate concentration has been maintained below the leucovorin (or levoleucovorin) treatment threshold for ≥3 days.

Adults

Methotrexate Toxicity

IV

50 units/kg as a single dose. Second dose not shown to produce further reduction in methotrexate concentrations.

Continue leucovorin (or levoleucovorin ) rescue. (See Specific Drugs under Interactions.) For first 48 hours after glucarpidase administration, administer leucovorin (or levoleucovorin) at same dosage administered prior to glucarpidase; beyond 48 hours, base dosage on methotrexate concentration. Continue leucovorin (or levoleucovorin) rescue until methotrexate concentration has been maintained below the leucovorin (or levoleucovorin) treatment threshold for ≥3 days.

Prescribing Limits

Pediatric Patients

Methotrexate Toxicity

IV

Single 50-unit/kg dose.

Adults

Methotrexate Toxicity

IV

Single 50-unit/kg dose.

Special Populations

No special population dosage recommendations at this time.

Cautions for Glucarpidase

Contraindications

• No known contraindications.

Warnings/Precautions

Sensitivity Reactions

Hypersensitivity

Risk of serious sensitivity reactions, including anaphylaxis.

Monitoring of Methotrexate Concentrations and Assay Interference

Plasma methotrexate concentrations measured by immunoassay within 48 hours following glucarpidase administration are unreliable.

During first 48 hours after glucarpidase administration, use chromatographic method to obtain reliable measurements of plasma methotrexate concentrations.

Continuation of Adjunctive Therapy

Following glucarpidase administration, continue leucovorin (or levoleucovorin ) rescue until methotrexate concentration has been maintained below the leucovorin (or levoleucovorin) treatment threshold for ≥3 days. (See Methotrexate Toxicity under Dosage and Administration and also see Specific Drugs under Interactions.)

Continue IV hydration and urinary alkalinization as indicated.

Antibody Formation

Development of antiglucarpidase antibodies reported. Detected between 7 days to 7 months following exposure to glucarpidase. Incidence appeared to be similar between patients receiving either 1 or 2 doses of glucarpidase.

Development of antiglucarpidase antibodies not expected to be clinically important considering the rapid time to maximum pharmacodynamic effect (15 minutes) and the recommended dosage regimen (i.e., single dose).

Specific Populations

Pregnancy

Category C.

Lactation

Not known whether glucarpidase is distributed into milk. Use with caution.

Pediatric Use

Efficacy established for treatment of toxic plasma methotrexate concentrations (>0.454 mcg/mL [1 µmol/L]) in pediatric patients with delayed methotrexate clearance due to renal impairment.

No overall differences in safety observed between pediatric patients (1 month to 17 years of age) and adults.

Geriatric Use

No overall differences in safety or efficacy in geriatric patients (≥65 years of age) compared with younger adults.

Hepatic Impairment

Not studied in patients with hepatic impairment.

Renal Impairment

Half-life is prolonged in patients with severe renal impairment. (See Special Populations under Pharmacokinetics.)

Common Adverse Effects

Paresthesia, flushing, nausea and/or vomiting, hypotension, headache.

Drug Interactions

Substrates of Glucarpidase

Possible decreased peak concentrations and AUC of the glucarpidase substrate. (See Specific Drugs under Interactions.)

Specific Drugs

Glucarpidase Pharmacokinetics

Absorption

Onset

Following a single 50-unit/kg dose, plasma methotrexate concentrations (measured by chromatographic method) decreased by ≥97% within 15 minutes.

Duration

Following a single 50-unit/kg dose, reductions in plasma methotrexate concentrations were maintained at >95% for up to 8 days.

Distribution

Extent

Distributed primarily in intravascular (i.e., extracellular) compartment; does not cross blood-brain barrier.

Not known whether glucarpidase is distributed into human milk.

Elimination

Half-life

5.6 hours (by enzymatic assay) or 9 hours (by enzyme-linked immunosorbent assay [ELISA]).

Special Populations

In patients with severe renal impairment (Cl_cr <30 mL/minute), half-life is prolonged (8.2 hours).

Stability

Storage

Parenteral

Powder for Injection

2–8°C. Do not freeze.

Following reconstitution, use immediately or store at 2–8°C for up to 4 hours; discard unused portions.

Actions

• Recombinant bacterial enzyme produced in Escherichia coli.

• Rapidly hydrolyzes methotrexate to its inactive metabolites 4-deoxy-4-amino-N¹⁰-methylpteroic acid (DAMPA) and glutamate.

• Because DAMPA and glutamate are principally metabolized hepatically, glucarpidase provides an alternative, nonrenal route for methotrexate elimination in patients with delayed methotrexate clearance due to renal impairment.

Advice to Patients

• Risk of hypersensitivity reactions, including anaphylaxis.

• Risk of infusion reactions. Importance of immediately reporting signs and symptoms of such reactions (e.g., fever, chills, flushing, feeling hot, rash, hives, itching, throat tightness or breathing difficulty, tingling, numbness, headache).

• Importance of continued monitoring of plasma methotrexate concentrations and renal function after discharge from the hospital.

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as any concomitant illnesses.

• Importance of informing patients of other important precautionary information. (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

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