The popular sugar substitute xylitol has always posed a deadly threat to dogs, but that threat is expanding as xylitol finds its way into vitamins and commonly prescribed drugs that used to be safe for canines—and now aren't.

According to veterinarian Patty Khuly, DVM, this expansion poses a risk that veterinarians, their pharmacists and their clients must all be aware of. "I used to recommend Flintstones vitamins for my patients," she said in Fully Vetted, a blog for those with an interest in pets. "Now I have to caution my clients to stick to pet-only brands and to be very diligent about reading labels. But it took months before I became aware of the change in this brand's ingredients."

Preparations of common human pediatric drugs prescribed by veterinarians for their own animal patients are now worth an extra look, said Dr. Khuly, as xylitol could be substituted into any of them without veterinarians being aware of the ingredient change. Pediatric elixers, in particular, are being reformulated for greater palatability, using xylitol.