b'SPECIAL REPORT SPONSORED BYSTACEY OKE, DVM, MSCWHAT WE KNOW ABOUT BISPHOSPHONATES FOR HORSESF or years, equine veterinarians relied on drugs, corrective shoeing, and surgery to help horses suffering from navicular syndrome to minimize discomfort and disease progression. Also known as podotrochlosis, navicular syndrome is the degeneration of the navicular bone nestled near the coffin bone near the rear of the horses foot, along with its associated structures. Management of this disease changed significantly in 2014 when the U.S. Food and Drug Administration approved bisphosphonates for treatment. Despite the availability of this newer treatment option, success ratesin terms of improvement in lameness gradehovered BIANCA MCCARTY PHOTOGRAPHYaround the 67% mark, leaving many horses in continued pain. Bisphosphonates used according to FDA-Recently, Texas A&M researchers reviewed the current body ofapproved guidelines knowledge surrounding bisphosphonates and their use in horses.do appear beneficial Their goal, they wrote, was to discuss the current understanding offor adult horses with navicular syndrome.the strengths and weaknesses of BPs [bisphosphonates] in equine veterinary medicine and highlight the future utility of these potentially highly beneficial drugs.Instead of looking at serum biochemical markers of bone turn-over or, more importantly, bone density, researchers on most equine BISPHOSPHONATE BASICS studies have used improvement in lameness grade as the endpoint. We spoke with Larry J. Suva, PhD, professor and departmentOne research group did examine serum markers of bone turnover in head of Veterinary Physiology and Pharmacology in the universitysbisphosphonate-treated horses, including two proteins found in bone: College of Veterinary Medicine and Biomedical Sciences, who definedosteocalcin (a marker of bone formation) and C-terminal collagen-I bisphosphonates as a class of phosphorus-containing chemicaltelopeptide (a marker of bone resorption). They noticed no change compounds that inhibit bone resorption. in either marker, as would be expected if bone treatment decreased Bone resorption is part of normal bone turnover to maintain aturnover yet lameness was significantly reduced. healthy musculoskeletal system that supports the horses current ath- However, in another study using horses casted on one leg, research-letic demands, he said. Two major types of cells are involved in boneers found an increase in serum markers of bone turnover. This was turnover: osteoblasts that lay down new bone and osteoclasts thatexpected because disuse results in increased bone resorption to adapt essentially remove bone.to decreased weight-bearing. After administering tiludronate, the in-The rationale for want- vestigators saw a significant reduction in markers of bone turnover. BISPHOSPHONATES:ing to stop bone resorptionThis latter report is one of the only studies demonstrating an anti-A class of phosphorus- is to increase navicular boneresorptive effect of bisphosphonates in horses, Suva said, adding, containing chemical compoundsstrength.These data also suggest alternative mechanisms of action of bisphos-that inhibit bone resorption. The idea may be that bonephonates to explain the improvement in lameness.mass increases with decreasedExamples of such mechanisms that have not yet been proven bone resorption, hence theinclude anti-inflammatory properties, decreased activity of enzymes navicular bone should be stronger, Suva said.that contribute to bone turnover, and altered growth factor effects. Two types of bisphosphonates exist: those that do and those thatEven though we do not have all the data we wish for, do not contain nitrogen. In horses, only two bisphosphonates, bothbisphosphonates used according to FDA approval guidelines in animals non-nitrogenoustiludronate and clodronateare FDA-approved.4 years of age or older do appear beneficial for horses with navicular They function differently than nitrogen-containing bisphosphonates;syndrome, Suva said. The concern is related to bisphosphonates however, both forms inhibit bone resorption, leading to increasedbeing used off-label for various other conditions in horses.bone mass and strength because osteoblasts continue to form bone.Interestingly, despite increased bone mass and strength being theOFF-LABEL USEobvious goals of bisphosphonate administration in horses, few studiesVeterinarians sometimes administer tiludronate or clodronate to have actually examined the effect of tiludronate or clodronate onhorses with chronic back soreness, osteoarthritis of the lower hock those parameters, said Suva.joint (bone spavin), and chronic lameness due to other causes.SpecRprt_Bisphosphonates_Dechra_8x10.indd 1 10/29/19 3:07 PM'