Effects of phenylbutazone on bone activity and formation in horses.
OBJECTIVE
To determine the effects of phenylbutazone (PBZ) on bone activity and bone formation in horses.


METHODS
12 healthy 1- to 2-year-old horses.


METHODS
Biopsy was performed to obtain unicortical bone specimens from 1 tibia on day 0 and from the contralateral tibia on day 14. Fluorochromic markers were administered IV 2 days prior to and on days 0, 10, 15, and 25 after biopsy was performed. Six horses received PBZ (4.4 mg/kg of body weight, PO, q 12 h) and 6 horses were used as controls. All horses were euthanatized on day 30 and tissues from biopsy sites, with adjacent cortical bone, were collected. Osteonal density and activity, mineral apposition rate (MAR), and percentage of mineralized tissue filling the biopsy-induced defects in cortical bone were assessed. Serum samples from all horses were analyzed for bone-specific alkaline phosphatase activity and concentration of PBZ.


RESULTS
MAR was significantly decreased in horses treated with PBZ. Regional acceleratory phenomenon was observed in cortical bone in both groups but was significantly decreased in horses treated with PBZ. Osteonal activity was similar at all time points in all horses. In control horses, percentage of mineralized tissue filling the cortical defects was significantly greater in defects present for 30 days, compared with defects present for 14 days. Differences in percentage of mineralized tissue were not detected in horses treated with PBZ.


CONCLUSIONS
PBZ decreased MAR in cortical bone and appeared to decrease healing rate of cortical defects in horses.
Rohde
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Department of Veterinary Clinical Sciences, The Ohio State University, Columbus 43210, USA.
Anderson
D E
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Bertone
A L
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Weisbrode
S E
SE
D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology* / Q000627:therapeutic use; D001706:Biopsy / Q000662:veterinary; D015519:Bone Density / Q000187:drug effects; D016723:Bone Remodeling / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D005260:Female; D005452:Fluoresceins / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D017102:Fracture Healing / Q000187:drug effects*; D050723:Fractures, Bone / Q000188:drug therapy / Q000601:surgery / Q000662:veterinary; D006253:Haversian System / Q000473:pathology; D006734:Horse Diseases / Q000188:drug therapy*; D006736:Horses; D007091:Image Processing, Computer-Assisted; D007118:Immunoassay / Q000662:veterinary; D008297:Male; D010118:Oxytetracycline / Q000737:chemistry; D010653:Phenylbutazone / Q000097:blood / Q000494:pharmacology* / Q000627:therapeutic use; D011448:Prostaglandin Antagonists / Q000494:pharmacology / Q000627:therapeutic use; D011897:Random Allocation; D013977:Tibia / Q000473:pathology / Q000502:physiology
D000894:Anti-Inflammatory Agents, Non-Steroidal; D005452:Fluoresceins; D005456:Fluorescent Dyes; D011448:Prostaglandin Antagonists; D000469:Alkaline Phosphatase; D010653:Phenylbutazone; C007740:fluorexon; D010118:Oxytetracycline