A compound called resiniferatoxin (RTX), which is derived from a cactuslike plant commonly found in Morocco, has long been pursued as a potential way to treat pain without dangerous opiates. RTX, in fact, is now in a Phase I/II study at the National Institutes of Health to treat intractable pain in people with end-stage cancer. But early trials in pet dogs have shown the toxin to be effective in relieving pain from canine bone cancer and osteoarthritis, too, and now ARK Animal Health, a subsidiary of Sorrento Therapeutics ($SRNE), has received encouragement from the FDA to pursue the compound for veterinary use. The agency granted the company Minor Use/Minor Species (MUMS) designation for its version of RTX, called ARK-001, which it is developing to treat pain in dogs with osteosarcoma. The designation will give ARK 7 years of market exclusivity if the drug is approved. Release