DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed solid tumor, including primary brain tumor

  • Progressive disease on standard therapy or for which no standard therapy exists
• No symptomatic brain metastases

PATIENT CHARACTERISTICS:

Age:

• 1 to 21

Performance status:

• Lansky 50-100% (age 10 and under)
• Karnofsky 50-100% (over age 10)

Life expectancy:

• At least 8 weeks

Hematopoietic:

• Absolute neutrophil count greater than 1,000/mm3
• Platelet count greater than 100,000/mm3

Hepatic:

• Bilirubin no greater than 1.5 mg/dL
• ALT no greater than 2.5 times upper limit of normal

Renal:

• Glomerular filtration rate at least 30 mL/min

Other:

• No active infection
• No serious uncontrolled medical disorder
• No psychiatric disorder or other disorder that would preclude study
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• At least 6 months since prior allogeneic bone marrow transplantation without evidence of acute or chronic graft versus host disease
• At least 3 months since prior autologous bone marrow or peripheral blood stem cell transplantation
• At least 4 weeks since prior immunotherapy and recovered
• No concurrent immunotherapy

Chemotherapy:

• No more than 3 prior chemotherapy regimens
• At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered
• No other concurrent chemotherapy

Endocrine therapy:

• Concurrent hormone replacement therapy or oral contraceptives allowed
• No other concurrent hormonal therapy

Radiotherapy:

• At least 4 weeks since prior radiotherapy (including for brain metastases) and recovered
• No concurrent radiotherapy

Surgery:

• Not specified

Other:

• No other concurrent investigational anticancer drugs
• No other concurrent antitumor therapy
• No concurrent anticonvulsants (e.g., phenytoin, phenobarbital, or carbamazepine) except gabapentin (Neurontin)