There are quite a few possible etiologies for Duncan's behavior
. Gastrointestinal disorders, dental
and oral disease, central nervous system disturbances such as brain tumors
or hydrocephalus, electrolyte imbalances, metabolic diseases, and toxins such as lead can induce licking, sucking, chewing, and picas (ingestion of inanimate objects), licking of owners, and air licking. Picas may also be caused by excessive restriction of calories (i.e. weight loss diets) and any medical condition that could cause polyphagia (increased hunger). Similarly, numerous medical conditions from Cushing's disease to diabetes
insipidus might induce polydipsia (increased thirst). Licking, chewing, polyphagia, polydipsia, and picas can also be a side effect of drug therapy. In geriatric pets, repetitive behaviors including licking, chewing, and picas might be associated with brain aging and cognitive dysfunction. Gastrointestinal irritation secondary to excessive uremic toxins in Duncan's bloodstream should be an important differential for his licking. Please note, too, that the adverse effect profile of the ACE inhibitors is principally GI distress and so we need to consider that he's experiencing an adverse drug reaction as well. I would see how an over the counter antacid such as famotidine
(Pepcid) dosed at 0.25 mg/lb and repeated in 12 hour intervals affects Duncan. The antacid must might provide enough comfort to stop his excessive licking behavior.Please respond with further questions or concerns if you wish.