Neurological

MDR1 (ABCB1) drug sensitivity

Urgent

Also known as: mdr1 mutation; mdr1; ivermectin sensitivity; abcb1

URGENT. See a veterinarian within hours, not days.

Overview

A single gene mutation that breaks the pump which normally keeps certain medication classes out of the brain. A dog carrying it can be poisoned by a perfectly normal dose of a perfectly normal drug — several antiparasitic classes, some anti-diarrhoeal, sedative, and chemotherapeutic agents among them. The affected classes are a matter for the veterinarian; the owner's job is simply to KNOW, and to tell every vet who treats the dog. It is common in the herding breeds — Collie, Border Collie, Australian Shepherd, Shetland Sheepdog, Old English Sheepdog, and their crosses — with the Rough Collie most affected of all. There is a cheap, definitive DNA test (a cheek swab), and it should be done once in the life of any herding-breed dog, ideally before it ever needs treating. This is one of the few entries in this encyclopedia where a single test, done once, can prevent a death.

What you would notice

Severe reaction after a routine medication — drooling, tremors, disorientation
Wobbliness, blindness, collapse, coma following a normal dose of a common drug
No signs whatsoever until the dog is given an affected medication class

Non-prescriptive. This entry deliberately does NOT name specific drugs, doses, routes, or durations. Treatment decisions rest with a licensed veterinarian who has examined your dog and considered its history.

Draft — vet review pending. This entry has not yet been signed off by a registered veterinarian.