DISEASE CHARACTERISTICS:

• Histologically confirmed anaplastic astrocytoma, anaplastic oligodendroglioma, or glioblastoma multiforme

• Progressive or recurrent disease previously treated with radiotherapy with or without chemotherapy

  • Prior low-grade disease that progressed to high-grade after therapy allowed
• Measurable disease by MRI or CT scan

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• Karnofsky 60-100%

Life expectancy:

• Not specified

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm3
• Hemoglobin at least 8.5 g/dL

Hepatic:

• Bilirubin no greater than 1.5 mg/dL
• Transaminases no greater than 4 times upper limit of normal

Renal:

• Creatinine no greater than 1.7 mg/dL

Other:

• No other malignancy within the past 5 years except curatively treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix or breast
• No serious concurrent infection
• No other medical illness that would preclude study
• Negative pregnancy test
• Not pregnant or nursing
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• See Disease Characteristics
• At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas) and recovered
• No more than 1 prior chemotherapy regimen

Endocrine therapy:

• Must be on stable dose of steroids for at least 5 days

Radiotherapy:

• See Disease Characteristics
• At least 3 months since prior radiotherapy and recovered
• No more than 1 prior course of radiotherapy

Surgery:

• Not specified

Other:

• No other concurrent investigational agents
• At least 10 days since prior anticonvulsant drugs that induce hepatic metabolic enzymes