Irinotecan With or Without Oxaliplatin in Treating Patients With Metastatic Colorectal Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed adenocarcinoma of the colon or rectum * Metastatic or recurrent disease that is not amenable to potentially curative treatment * Progressive or recurrent disease during or after 1, and only 1, regimen of fluorouracil with or without leucovorin calcium or during or within 6 months after adjuvant chemotherapy with fluorouracil and leucovorin calcium PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * Karnofsky 50-100% Life expectancy: * Not specified Hematopoietic: * Absolute neutrophil count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 Hepatic: * Bilirubin no greater than 1.5 times upper limit of normal (ULN) * SGOT/SGPT no greater than 2 times ULN (no greater than 5 times ULN if liver metastases present) * Alkaline phosphatase no greater than 2 times ULN (no greater than 5 times ULN if liver metastases present) Renal: * Creatinine no greater than 1.5 times ULN Cardiovascular: * No unstable angina * No New York Heart Association class III or IV congestive heart failure * No serious cardiac arrhythmia * No history of cardiac toxicity from fluorouracil/leucovorin calcium * No myocardial infarction within past 6 months Pulmonary: * No interstitial pneumonia or extensive and symptomatic fibrosis of the lung Other: * No uncontrolled predisposing colonic or small bowel disorder * No prior chronic enteropathy, chronic diarrhea, or unresolved bowel obstruction/subobstruction * No diabetes * No active infection * No known current peripheral neuropathy * No concurrent active cancer except curatively treated nonmelanoma skin cancer or carcinoma in situ of the cervix * No intolerance of appropriate antiemetics * No history of anaphylaxis or potential intolerance to atropine sulfate or loperamide * Not pregnant or nursing * Negative pregnancy test PRIOR CONCURRENT THERAPY: Biologic therapy: * Not specified Chemotherapy: * See Disease Characteristics * At least 3 weeks since prior chemotherapy * No prior irinotecan or oxaliplatin * No other prior chemotherapy agents except fluorouracil with or without leucovorin calcium as first-line therapy for metastatic disease or in the adjuvant setting Endocrine therapy: * Not specified Radiotherapy: * Prior radiotherapy to non-target lesions allowed * No prior radiotherapy to target lesions unless disease progression is documented within the radiation port * At least 3 weeks since prior radiotherapy Surgery: * At least 4 weeks since prior major surgical procedure and recovered * Prior surgery for primary tumor or metastasis allowed Other: * At least 30 days since prior investigational drug * No concurrent investigational agents