Not drinking while on antibiotics

Hello,

My chinchilla was prescribed oral antibiotics with a probiotic as well as eye drops a week ago. We noticed that he has not been really drinking, but he is still eating. Yesterday, his droppings were very small, dry, and a very light color. This tells me he is dehydrated. Is this a normal reaction to antibiotics, or should I be concerned? I am going to start syringing water in his mouth just so I know he is getting some type of fluid.