suggestion for switching dog food brands
What my vet told me is that when switching brands you must do so gradually mixing in the brand you are switching to (Purnina, you said.) So start off with a bowl of 90% Euk and 10% Purina and she how s/he does with that. Each day add a little more Purina and a little less Euk. This worked for me when I switched dog food brands but there is the chance that Purina just won't agree with your maltese. In that case you would want to find him/her another dog food altogether.
Hope that helps!
:D :) ;)