My dog weighed 28-30lbs and the correct dose for her was 500mg Glucosamine
per day. The vet said the 'human' Glucosamine
was fine to use, so long as the dosage
was correct for the dog's weight.
So it depends what your dog's weight is, how much you can increase the dose.
As far as I can make out, dogs (and humans too) respond differently to Glucosamine. With some there are great results, and with some, not much improvement.
You could mention this to your vet perhaps.