PRIOR CONCURRENT THERAPY: Biologic therapy: At least 3 months since prior bone marrow transplantation Recovered from prior biologic therapy No concurrent anticancer biologic therapy Chemotherapy: Recovered from prior chemotherapy No concurrent anticancer chemotherapy Endocrine therapy: Recovered from prior endocrine therapy No concurrent anticancer endocrine therapy No concurrent dexamethasone or other steroids as antiemetic agents Radiotherapy: No concurrent anticancer radiotherapy Surgery: Not specified Other: No concurrent dairy products for 2-4 hours before, during, or 2-4 hours after study drug No concurrent trimethoprim-sulfamethoxazole or dapsone as prophylaxis for Pneumocystis infection No concurrent multivitamins containing folic acid