You can give lasix more frequently if needed ..... instead of once every 12 hours, you could give once every 8 hours (ie 3xs/day), or once every 6 hrs (ie 4xs/day) and/or increase the dose
But watch out for dehydration, give lots of tasty treats (such as watermelon) to keep him hydrated and be prepared to give sub-Q fluids if necessary
River is on Lasix 3xs/day