Inclusion Criteria:

- Written informed consent by patient or legally valid representative

- Patients receiving high-dose MTX (>1 g/m2 body surface area (BSA) given as an
infusion over 24 hours) for the treatment of ALL, NHL or a solid tumour (e.g.
osteosarcoma)

- Age ≥ 18 years

- Serum MTX >5 µmol/L 42 hours or later after the start of MTX infusion, or serum MTX
>1 μmol/L 42 hours or later after the start of MTX infusion together with renal
insufficiency, or serum MTX >0.4 µmol/L 48 hours or later after the start of MTX
infusion together with renal insufficiency. Renal insufficiency was defined as serum
creatinine >1.5 × the upper limit of normal (ULN) and/or oliguria (urine output < 500
mL/24 hours despite adequate hydration, diuretics and alkalinisation).

Exclusion Criteria:

- Pregnant or lactating females

- Unwillingness of patient or relative/legal representative to give informed consent