Tilmicosin
Tilmicosin is a macrolide antibiotic. It is distributed under the brand name Micotil. It is used in veterinary medicine for the treatment of bovine respiratory disease and enzootic pneumonia caused by Mannheimia (Pasteurella) haemolytica in sheep. In humans, Tilmicosin causes fatal cardiotoxic effects at amounts greater than 1 milliliter when injected, something most commonly seen in veterinary personnel and farmers. Tilmicosin, like most macrolides, is a Calcium channel blocker. However, because Micotil is formulated for animals like cows, it has exceptionally more potent Ca channel blocking effects in humans with a dose of .5 mL causing significant poisoning and a dose of 5-6 ml being lethal. References

Macrolide antibiotics
Veterinary drugs