Wouldn't be as much punishment as you think.
1. The amount of IVM in the standard horse paste syringe is only the equivalent of 2 days of treatment for an infected person.
2. Some claim to have been taking the horse paste routinely with no ill effects (not to mention the prophylactic benefit). Some have said, "tastes bad", however.
3. High doses... up to 10x the recommended dosage have been tested and have been well-tolerated with no ill effect. (I suspect ALL of the stories of people "overdosing on horse paste" were fabricated. Likely the only genuine stories of overdosing on IVM, if any at all, were about people trying to commit suicide by swallowing a whole bottle of pills.)