The ivermectin problem is not as common in GSDs but to be safe you can check with a veterinarian.
MDR1 Gene Mutation/Heartguard/Ivermectin WARNING
Many herding dog breeds are afflicted with a mutation of the multi-drug resistance (mdr1) gene. This gene encodes a protein (P-glycoprotein) that is responsible for removing certain drugs and toxins from the brain. Dogs that carry the mdr1 genetic defect cannot rid their brains of the problem drugs. The result is a neurotoxic buildup that can cause abnormal neurological symptoms and/or death
Dogs from affected breeds who carry the mutated gene OR who have not been tested for the mutation should avoid using drugs from the MDR1 Problem Drugs List . The list is divided into drugs known to cause mdr1 mutation problems and drugs suspected of causing mdr1 mutation problems.
The most commonly prescribed drug on the list is ivermectin, a wormer used in many canine heartworm preventative treatments including Heartguard, Iverhart, Tri-Heart and Advantage DUO.
Smitty (rescue) Ilda WGSL 4/28/10 Autumn Australian Shepherd 10/9/11
"After awhile, to the deer hunter, everything begins to look like a deer"