Lidocaine is a potent substance that doctors and veterinarians use as an injected or topical pain reliever. While the ointment is very effective in humans and most animals, it’s less effective in horses. However, a German research group has determined that microneedles could be a pointed new solution to this long-standing problem.

“Delivering drugs topically (through the skin) has multiple benefits for horses,” said Jessica Stahl, DrMedVet, of the University of Veterinary Medicine Hannover Pharmacology, Toxicology, and Pharmacy Institute. “There’s no pain, you get constant plasma levels, the drug is delivered over a long period of time, and the skin acts as a reservoir for storage of the drug.”

Although they’d like to reap those benefits, veterinarians have not been successful in getting lidocaine into horses’ systems in effective quantities using a topical preparation. That’s because the skin has a resistant layer called the stratum corneum, and the equine version seems to block certain drugs—including lidocaine—from seeping through into the body parts (muscle, tendons, etc.) that need the pain relief.

Stahl said that for years, people have tried to “enhance” lidocaine’s passage through the skin by applying various other chemicals, like alcohol, sulfoxides, and polyols. But her new study indicates that none of these “enhancers” work—and in fact, some make the drug’s permeation even worse