You will take Dexamethasone tablets by mouth, 2 times a day on the day before, the day of, and the day after each dose of Pemetrexed. Dexamethasone is taken to prevent rashes. If you could not or did not take Dexamethasone the day before and/or the day of Pemetrexed, you may be given Dexamethasone by IV over 20 minutes, 30 minutes before the infusion of Pemetrexed.