Allermi formulas contain xylitol which, in large quantities, can be toxic to dogs. One of the basic principles of toxicology is that the dose makes the poison. There is a relatively low amount of xylitol in each Allermi bottle, so a dog would have to ingest quite a bit to be a concern.
Many Allermi formulas contain oxymetazoline, which is also concerning when ingested by dogs. The quantity of oxymetazoline in Allermi is also quite low, far lower than other oxymetazoline products.
If you know or suspect that your dog ingested any amount of your Allermi medication, please contact the ASPCA Animal Poison Control Center at (888) 426-4435. The ASPCA Animal Poison Control Center (APCC) is your best resource for any animal poison-related emergency, 24 hours a day, 365 days a year.