Background Medulloblastoma is one of the most frequent malignant brain tumours in infancy. Conventional treatment is based on combined radiotherapy and chemotherapy after surgical resection of the tumour. The chemotherapy consists of combinations of various anticancer agents, including methotrexate. Methotrexate is administered in intravenous infusion at high doses combined with intrathecal injection at low doses. The use of fluorescence polarisation immunoassay (FPIA) to monitor blood methotrexate levels is widely validated, but there have been few studies on its application to analyse cerebrospinal fluid (CSF) concentrations of this drug.
Purpose To analyse cerebrospinal fluid (CSF) concentrations of methotrexate by fluorescence polarisation immunoassay (FPIA) in patient with medulloblastoma.
Materials and methods A 22-month-old female diagnosed with medulloblastoma underwent intensive chemotherapy. The regimen was three two-month courses of chemotherapy with methotrexate and other anticancer agents. The patient has received one complete course to date. In the first week, 2 mg of methotrexate were administered intraventricularly via Ommaya reservoir for four days, followed by intravenous cyclophosphamide for three days. In week 3, 2 mg of intraventricular methotrexate was administered in combination with a 24-h intravenous infusion of 2.7 g methotrexate and INTRAVENOUS infusion of vincristine on day 1 and was administered alone on day 2. The treatment in week 5 was identical to that in week 3. Finally, in week 7, the patient received 2 mg of intraventricular methotrexate daily for four days followed by intravenous carboplatin and etoposide for three days. Methotrexate CSF samples were drawn before the first intraventricular injection and at 24 h after each intraventricular administration. CSF methotrexate levels were determined by FPIA using an Abbot TDX analyser.
Results CSF methotrexate levels were measured with the following results: week 1, day 1: 14.26 x 10 -6 M, day 2: 218 x 10 −6 M, day 3: 0.75 x 10 −6 M, day 4: 0.33 x 10 −6 M; week 3, day 1: 0.05 x 10 −6 M, day 2: 2.96 x 10 −6 M; week 5, day 1: 0.02 x 10 −6 M, day 2: 2.16 x 10 −6 M; week 7, day 1: 0 x 10 −6 M, day 2: 1.46 x 10 −6 M, day 3: 0.94 x 10 −6 M, and day 4: 1.07 x 10 −6 M; the mean value was 1.38x10−6 M. Values on day 1 of each cycle were obtained prior to the intraventricular injection and were determined solely to confirm the virtual absence of methotrexate before initiating the next intraventricular administration cycle; therefore, day 1 values were not considered in the calculation of the mean CSF concentration. Values on days 1 and 2 of week 1 were excluded from our analysis because the same route was used for the intrathecal injection and subsequent CSF sample extraction; therefore, the corresponding samples were contaminated.
Conclusions FPIA proved to be a reliable method to measure CSF fluid methotrexate concentrations, within published ranges, although further studies are required to verify these findings.
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