Pemetrexed (Alimta Â®). Pemetrexed is a chemotherapy drug | used to treat non-small cell lung cancer | and pleural mesothelioma | (a type of cancer that affects the lining of the lung).emetrexed is a chemotherapy drug | used to treat non-small cell lung cancer | and pleural mesothelioma | (a type of cancer that affects the lining of the lung).