Carboplatin Plus Irinotecan in Treating Patients With Glioblastoma Multiforme

DISEASE CHARACTERISTICS: Histologically confirmed glioblastoma multiforme Measurable disease No CNS metastases or carcinomatous meningitis PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 OR Karnofsky 70-100% Life expectancy: At least 12 weeks Hematopoietic: Granulocyte count greater than 1,500/mm^3 Platelet count greater than 100,000/mm^3 Hemoglobin at least 9.0 g/dL Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT no greater than 3 times upper limit of normal (ULN) (5 times ULN if liver involvement) No known Gilbert's syndrome Renal: Creatinine no greater than 1.5 mg/dL Cardiovascular: No myocardial infarction within the past 6 months No congestive heart failure requiring therapy Other: HIV negative No active or uncontrolled infection No psychiatric disorder that would preclude study No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix No uncontrolled diabetes mellitus (i.e., random blood sugar of 200 mg or more) No other severe disease that would preclude study Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy or biologic therapy No concurrent sargramostim (GM-CSF) No concurrent filgrastim (G-CSF) with course 1 No concurrent immunotherapy Chemotherapy: No prior chemotherapy No other concurrent chemotherapy Endocrine therapy: Must have maintained a stable or decreasing dose of corticosteroids for 2 weeks prior to study Concurrent corticosteroids for cerebral edema allowed No concurrent anticancer hormonal therapy Radiotherapy: No prior radiotherapy No concurrent radiotherapy Surgery: At least 2 weeks since prior surgery Other: No other concurrent investigational agent or participation on any other clinical study No concurrent immunosuppressive drugs No concurrent phenobarbital or valproic acid No concurrent anticonvulsants except carbamazepine or gabapentin No concurrent prochlorperazine on day of irinotecan treatment