No, keep going with him. If you're getting antibiotic from the vet get some levamisole or ivermectin wormer too. If the vet doesn't keep it, if you can find a feed merchant for farmers, they may keep it. In fact, you will need so little a friendly farmer would probably give you some

Squirt it directly down his beak.
I've had a very sick gander I bought in a dreadful state and he is mending well now, with care, good food and medicine. Good luck with yours
