They are required to take folic acid by mouth every day for 5 days before the first dose of pemetrexed and continuing until 3 weeks after your last dose of pemetrexed. They will also receive an injection of vitamin B12 into your muscle before first dose of pemetrexed. The vitamin B12 injection will be repeated every 9 weeks until 3 weeks after their last dose of pemetrexed.