While on study, you will be required to take folic acid by mouth every day for 5-7 days before the first dose of pemetrexed and continuing until 3 weeks after your last dose of pemetrexed. You will also receive an injection of vitamin B12 into your muscle 1 to 2 weeks before your first dose of pemetrexed. The vitamin B12 injection will be repeated every 9 weeks until 3 weeks after your last dose of pemetrexed. It is very important that folic acid and vitamin B12 be given to decrease the risk of severe side effects from the pemetrexed.