PRIOR CONCURRENT THERAPY: At least 4 weeks since prior therapy for cancer and recovered Biologic therapy: No concurrent immunotherapy No concurrent filgrastim (G-CSF), sargramostim (GM-CSF), or epoetin alfa Chemotherapy: No prior nitrosoureas, mitomycin, or irinotecan No prior high dose chemotherapy in support of peripheral blood stem cell transplantation No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal therapy Radiotherapy: No prior irradiation of pelvis No concurrent radiotherapy Surgery: No prior gastrectomy or total colectomy Other: At least 1 week since prior anticonvulsants No other concurrent investigational drugs No combination anticholinergic medications containing barbiturates (e.g., Donnatol)