Responses to meloxicam , a cyclooxygenase ( COX ) -2 preferential agent , appeared comparable to those detected after phenylbutazone treatment , which suggested that COX-2 was the mediator of prostanoid-induced changes to renal function in horses and indicated that COX-2-preferential agents would be likely to have adverse renal effects similar to those for nonselective COX inhibitors in volume-depleted horses .