Pathophysiologic effects of phenylbutazone on the right dorsal colon in horses.
OBJECTIVE
To determine pathophysiologic effects of phenylbutazone on the equine right dorsal colon (RDC).


METHODS
12 healthy adult horses.


METHODS
A controlled crossover observational study was conducted. Clinical and serum variables, colonic inflammation (histologic grading), and measurement of myeloperoxidase (MPO) activity, malondialdehyde (MDA) and prostaglandin E(2) (PGE(2)) concentrations, ingesta volatile fatty acid (VFA) content, and arterial blood flow in the RDC were evaluated for a 21-day period in horses administered phenylbutazone (8.8 mg/kg, PO, q 24 h) or a control substance.


RESULTS
Data from 8 horses were analyzed. Plasma albumin concentrations decreased significantly from days 10 to 21 during phenylbutazone treatment, compared with results during the same days for the control treatment. Phenylbutazone treatment caused neutropenia (< 3.0 x 10(3) cells/microL). No other clinical or hematologic abnormalities were detected for phenylbutazone or control treatments. Two horses developed colitis while receiving phenylbutazone. No significant differences were detected in the RDC between phenylbutazone and control treatments for MPO activity, MDA and PGE(2) concentrations, and histologic evidence of inflammation. Arterial blood flow in the RDC was significantly increased during phenylbutazone treatment, compared with values for the control treatment. Differences were identified in VFA production during phenylbutazone treatment, compared with the control treatment, with a decrease in acetic acid concentrations over time.


CONCLUSIONS
Prolonged phenylbutazone administration caused hypoalbuminemia, neutropenia, changes in RDC arterial blood flow, and changes in VFA production. Veterinarians should monitor serum albumin concentrations and neutrophil counts and be cautious when making dosing recommendations for phenylbutazone treatment of horses.
McConnico
Rebecca S
RS
Department of Veterinary Clinical Sciences, Equine Health Studies Program, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Morgan
Timothy W
TW
Williams
Cathleen C
CC
Hubert
Jeremy D
JD
Moore
Rustin M
RM
D000818:Animals; D003092:Colitis / Q000139:chemically induced / Q000473:pathology / Q000662:veterinary*; D003106:Colon / Q000098:blood supply / Q000187:drug effects* / Q000503:physiopathology; D018592:Cross-Over Studies; D005227:Fatty Acids / Q000378:metabolism; D006734:Horse Diseases / Q000139:chemically induced* / Q000473:pathology*; D006736:Horses; D008315:Malondialdehyde / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism; D010653:Phenylbutazone / Q000633:toxicity*; D011458:Prostaglandins E / Q000378:metabolism; D012039:Regional Blood Flow / Q000187:drug effects; D013997:Time Factors
D005227:Fatty Acids; D011458:Prostaglandins E; D008315:Malondialdehyde; D009195:Peroxidase; D010653:Phenylbutazone