Finding the cause of sudden seizures in previously healthy dogs may require a neurology or internal medicine work-up, but the ASPCA Animal Poison Control Center notes that often the problem can be traced to a toxin exposure.
Before you recommend an MRI, refer to this chart to see if the pet has potential exposure to one of the items. Be mindful that many of the medications commonly used in veterinary medicine are on this list because they cause concern in overdose situations or when given via an incorrect route (ie giving Penicillin G IV).
Fluorouracil (5-FU) cream
Procaine Penicillin G
Any medications with the potential to cause hypoglycemia (such as sulfonylureas)