Triple Intrathecal Chemotherapy Dosing
For adults, administer methotrexate 15 mg, cytarabine 30-40 mg, and hydrocortisone 15-20 mg intrathecally as triple therapy. For pediatric patients, doses are age-adjusted as detailed below.
Adult Dosing
The most recent guideline evidence establishes the following adult triple intrathecal therapy (TIT) regimen 1:
- Methotrexate: 15 mg
- Cytarabine: 40 mg
- Hydrocortisone: 20 mg
This dosing is supported across multiple NCCN guidelines for lymphomas and leukemias 2. Importantly, no dosage adjustment is made based on weight or body surface area in adults 3.
Administration Schedule
The typical schedule follows an induction-consolidation-maintenance pattern 3:
- Induction: Twice weekly until CSF clears (typically 8 treatments)
- Consolidation: Weekly for 4 treatments
- Maintenance: Monthly thereafter
For individual agents when used as monotherapy, methotrexate is typically dosed at 10-15 mg and cytarabine at 30-100 mg 3.
Pediatric Dosing (Age-Adjusted)
Pediatric triple intrathecal therapy doses are strictly age-based, not weight-based 4, 5:
- Age 0-0.99 years: Methotrexate 7.5 mg + hydrocortisone 7.5 mg + cytarabine 15 mg
- Age 1-1.99 years: Methotrexate 8 mg + hydrocortisone 8 mg + cytarabine 16 mg
- Age 2-2.99 years: Methotrexate 10 mg + hydrocortisone 10 mg + cytarabine 20 mg
- Age 3-8.99 years: Methotrexate 12 mg + hydrocortisone 12 mg + cytarabine 24 mg
- Age ≥9 years: Methotrexate 15 mg + hydrocortisone 15 mg + cytarabine 30 mg
Critical Safety Considerations
Leucovorin Rescue for Methotrexate
Oral leucovorin (folinic acid) 10 mg should be administered twice daily, beginning on the day of intrathecal methotrexate treatment and continuing for 3 days 3. This mitigates systemic toxicity from methotrexate reabsorption without interfering with CSF drug levels, as leucovorin does not cross the blood-brain barrier in sufficient amounts.
Dexamethasone with Liposomal Cytarabine
If using liposomal cytarabine (DepoCyt) instead of conventional cytarabine, oral dexamethasone 4 mg twice daily for 5 days is mandatory to prevent chemical meningitis 3. For pediatric patients, dexamethasone dosing is 0.15 mg/kg/dose twice daily for 5 days 3.
Contraindications and Precautions
Relative contraindications to intrathecal methotrexate include 3:
- Renal insufficiency
- Large pleural effusions or ascites (third-space fluid collections)
- Abnormal CSF flow
These conditions increase risk of systemic methotrexate accumulation and myelosuppression. Patients with poor bone marrow reserve are at particular risk.
Drug interactions: Methotrexate toxicity increases with concurrent aspirin, phenytoin, sulfonamides, or tetracycline due to protein displacement 3.
Neurotoxicity Risk
Leukoencephalopathy may occur, particularly with 3:
- Abnormal CSF flow
- Concurrent CNS radiation therapy
- Prolonged treatment duration
Treatment beyond 6 months in responding patients may be unnecessary and increases neurotoxicity risk 3.
Clinical Context
Triple intrathecal therapy is widely used in Spain and incorporated into PETHEMA protocols for lymphoblastic lymphoma and Burkitt lymphoma 1. While TIT has proven efficacy in treating CNS relapse, evidence supporting its use in prophylactic settings over methotrexate monotherapy remains limited 1. The choice between triple therapy and methotrexate monotherapy should consider the specific malignancy, risk stratification, and institutional protocols.
For CNS prophylaxis in high-risk patients, intrathecal methotrexate 12 mg once per cycle for 4-6 doses is an alternative to triple therapy 1. High-dose intravenous methotrexate (≥3 g/m²) can also achieve therapeutic CSF levels and may be considered as an alternative or adjunct to intrathecal administration 3, 1.