Pemetrexed Disodium and Gemcitabine in Treating Patients With Advanced Cancer of the Urothelium

DISEASE CHARACTERISTICS: * Histologically confirmed cancer of the urothelium (renal pelvis, ureter, bladder, or urethra) * Any of the following types: * Transitional cell carcinoma (TCC) * Mixed histologies containing a component of TCC * Non-TCC of the urothelium (renal pelvis, ureter, bladder, or urethra) * Progressing regional or metastatic disease * Measurable disease * No clinical evidence of CNS metastases * No evidence of clinically significant (by physical exam or plain film) third-space fluid collections (pleural effusions or ascites) PATIENT CHARACTERISTICS: Age * 18 and over Performance status * ECOG 0-2 Life expectancy * Not specified Hematopoietic * Granulocyte count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 9 g/dL Hepatic * AST no greater than 3 times upper limit of normal (ULN) * Bilirubin no greater than 1.5 times ULN Renal * Creatinine clearance at least 45 mL/min Cardiovascular * No history of severe cardiovascular disease (i.e., American Heart Association class III or IV heart disease) * No uncontrolled congestive heart failure * No ventricular dysrhythmias Other * Not pregnant or nursing * Fertile patients must use effective contraception * No active unresolved infection * No other prior malignancy unless curatively treated and disease free for an appropriate (disease-specific) period of time * Able and willing to receive folic acid and cyanocobalamin supplementation PRIOR CONCURRENT THERAPY: Biologic therapy * No prior systemic biologic response modifier therapy Chemotherapy * No prior systemic chemotherapy for metastatic disease * More than 1 year since prior neoadjuvant or adjuvant chemotherapy Endocrine therapy * Not specified Radiotherapy * At least 4 weeks since prior radiotherapy and recovered * No prior pelvic radiotherapy * No concurrent radiotherapy Surgery * At least 4 weeks since prior major surgery and recovered Other * More than 7 days since prior parenteral antibiotics * No salicylates for 2 days before, during, and for 2 days after administration of pemetrexed disodium * No nonsteroidal anti-inflammatory drugs for at least 5 days before, during, and for 2 days after administration of pemetrexed disodium