The invention includes methods, compositions, and kits useful for treating a viral infection by coadministering 6-(3-chloro-2-fluorobenzyl)-1-[(2S)-1-hydroxy-3-methylbutan-2-yl]-7-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid or a pharmaceutically acceptable salt thereof, with lopinavir or a pharmaceutically acceptable salt thereof.