Pet Medication Dose Calculator

Cats are missing several liver enzymes (especially the UGT1A6 glucuronidation pathway) that dogs and humans use to process common drugs. Salicylates like aspirin and the bismuth subsalicylate in Pepto-Bismol build up to toxic levels in cats because they cannot clear them at a normal rate, and a single regular-strength dose can cause GI ulceration or fatal toxicity. Loperamide (Imodium) crosses the blood-brain barrier in cats much more readily than in dogs and can cause severe sedation, agitation, or respiratory depression. This is why the calculator filters cats to only the few OTC drugs vets reference for them (diphenhydramine, famotidine, meclizine) and blocks the rest with a contraindication warning.

The MDR1 (Multi-Drug Resistance 1) gene codes for a protein that pumps certain drugs out of the brain. Dogs with the MDR1 mutation cannot pump loperamide out, so even a normal dose can cause severe neurological side effects: profound sedation, ataxia, seizures, or coma. The mutation is common in herding breeds: Collies (up to 70 percent), Australian Shepherds, Old English Sheepdogs, Shetland Sheepdogs, Long-haired Whippets, Silken Windhounds, and mixes that include any of those breeds. If you have not had your dog DNA-tested for MDR1 and the breed is at risk, do not give Imodium. Washington State University's veterinary lab runs an inexpensive MDR1 test by cheek swab.

Diphenhydramine (Benadryl) is most commonly used for mild allergic reactions, including itchy skin from environmental allergens, mild reactions to insect stings, vaccine reactions, and mild hay-fever-style symptoms. It also produces mild sedation in many dogs and is sometimes used as a low-grade calming aid for car rides, thunderstorms, or grooming. It has mild anti-nausea effects, so it can help with motion sickness, though meclizine is usually more effective. Benadryl will not stop a severe anaphylactic reaction (facial swelling, breathing difficulty, collapse) and is not a substitute for an emergency vet visit if your dog is in respiratory distress.

Call the vet if symptoms last more than 48 hours, if you see blood in vomit or stool, if your pet is unusually lethargic or unresponsive, if they refuse food or water for more than 24 hours, if they have a fever (over 103.5 degrees F rectal), if they are vomiting more than two or three times in a day, or if symptoms are getting worse instead of better. Puppies under 16 weeks, senior pets, pregnant or nursing animals, and pets with known kidney, liver, or heart disease should be seen by a vet first rather than dosed at home. Any new lump, swelling, breathing difficulty, persistent cough, or change in urination pattern needs an exam, not OTC medication.

Two national US hotlines are staffed 24/7 by veterinary toxicologists. The ASPCA Animal Poison Control Center (888-426-4435) charges a per-incident fee, currently around $95, that covers the case and any follow-up consults with your treating vet. The Pet Poison Helpline (855-764-7661) charges a similar per-incident fee, around $89. Both will give you a case number to share with your local vet or ER, which speeds up treatment significantly. If you suspect poisoning (ingested human medication, chocolate, xylitol, antifreeze, rat bait, grapes, lily plants, or any unknown substance), call before driving anywhere: the toxicologist may tell you to induce vomiting at home, or may tell you to skip that and drive straight to the ER.