NSAIDs Before PRP or PRF: What New Equine Research Shows

A sore horse's week tends to follow a familiar order. The anti-inflammatory goes in first, because the horse is uncomfortable and the vet is two days out. Then the vet arrives, the leg is scanned, and a decision is made to treat it with something made from the horse's own blood. By the time the needle goes into the jugular vein to collect that blood, the horse may have been on flunixin or phenylbutazone for several days. Whether that changes what ends up in the syringe is easy to overlook.

A study published online on October 30, 2026 in the Equine Veterinary Journal suggests it can. Researchers at North Carolina State University's College of Veterinary Medicine found that horses given a multi-day course of flunixin meglumine produced platelet-rich fibrin with lower concentrations of several growth factors, the very signals the treatment exists to deliver. The finding is narrow and the study is small. Read alongside two earlier studies from the University of Pennsylvania, it makes a strong case that one simple step, a full day without anti-inflammatories before the blood draw, should be routine in every barn.

What the North Carolina Study Measured

The paper, led by Katrina Jones with senior author Michala de Linde Henriksen, compared 12 horses that had received full-dose flunixin meglumine, 1.1 mg/kg (0.5 mg/lb) twice daily, for three or more days against 12 control horses with no anti-inflammatory exposure for at least three months. The team prepared plasma, solid platelet-rich fibrin (PRF) and liquid PRF from each horse, measured growth factors and inflammatory signaling molecules, called cytokines, with immunoassays, and measured flunixin in the plasma directly.

The result that matters for riders is specific. Solid PRF from the control horses contained more transforming growth factor beta 1 (TGF-β1), platelet-derived growth factor (PDGF) and vascular endothelial growth factor A (VEGF-A) than solid PRF from the horses given flunixin. The authors' conclusion is plainly worded: "Systemic NSAID administration appears to reduce concentrations of key growth factors in solid PRF."

The growth factors that platelets release, as Lauren Schnabel of NC State explained in a 2025 article for Today's Veterinary Practice, modulate healing by promoting new blood vessel formation and cell migration, among other effects. A platelet product carrying less of them is, at least on paper, a weaker version of the thing the owner is paying for.

The Case That It Does Not Matter

The opposing evidence deserves a full hearing, because it is good evidence. In 2024, a team at the University of Pennsylvania School of Veterinary Medicine, led by Kara Brown with senior author Kyla Ortved, published two crossover studies in the American Journal of Veterinary Research. Both used six university-owned horses and processed their blood into autologous protein solution (APS) using Pro-Stride and platelet-rich plasma (PRP) using Restigen.

The first tested single doses of phenylbutazone, firocoxib, flunixin meglumine and ketoprofen, with blood processed before dosing and six hours after. It found no significant differences in growth factor or cytokine concentrations for any of the four drugs. The second went further, giving phenylbutazone twice daily or firocoxib once daily by mouth for six days, then collecting blood on day 7, one day after the last dose. Again, the team found no significant differences in the cytokines and growth factors it measured. The authors concluded that vets can recommend these oral anti-inflammatories before blood is obtained for PRP or APS, provided a single-day washout is used.

That second study is the strongest argument against alarm. It covers two everyday oral anti-inflammatories, over a realistic stretch of days, in the two platelet products it tested. Its message to owners is reassuring.

Reading the Results Together

The studies are less contradictory than they first appear, because they asked different questions. Penn's six-day study built a day's washout into its design and tested phenylbutazone and firocoxib in PRP and APS. NC State tested multi-day flunixin, a drug Penn studied only as a single dose, in PRF, a second-generation platelet concentrate that releases its contents from a fibrin matrix. The fair conclusion is that a short course followed by a day off showed no measurable effect on PRP and APS, while a sustained course of flunixin was associated with lower growth factors in solid PRF.

The limitations cut in both directions. The NC State design was cross-sectional, comparing horses that had received flunixin with a separate group of horses that had not, so it cannot rule out other differences between the groups; the authors list the small sample and the incomplete characterization of the horses' metabolic and endocrine status among its limitations. Its clinical setting was the eye, where PRF is used as a regenerative therapy for corneal healing and where horses with ulcerative keratitis often receive systemic anti-inflammatories. A companion paper from largely the same group, published in Veterinary Ophthalmology in November 2026, found that flunixin made no significant difference to two antiprotease proteins in the same blood products, so the effect appears selective rather than wholesale. None of these studies measured whether a horse healed faster or slower. Each measured the contents of the product.

The washout is the part of the evidence that every study points toward, and it costs an owner nothing but a day.

Why the Sport Horse Owner Should Care

Owners agree to platelet products for tendon injuries on the strength of trials like the one run at the University of Veterinary Medicine Hannover by Florian Geburek and colleagues, with Utrecht University's Hans van Schie. That randomized, placebo-controlled trial followed 20 horses with naturally occurring superficial digital flexor tendon injuries and was published in BMC Veterinary Research in 2016. A single intralesional PRP injection given up to eight weeks after the onset of clinical signs reduced lameness earlier than saline and was associated with more advanced organization of the repair tissue. At 12 months, 8 of 10 PRP horses had returned to their previous or a higher level of performance, against 5 of 10 controls; at 24 months the figures were 6 of 10 and 5 of 10.

Those are meaningful but modest margins, and they narrowed with time. A benefit of that size leaves little room to give any of it away through poor timing. The Hannover authors recommended treating earlier. The newer evidence suggests that earlier should still include a clean day before the blood is drawn.

The Position NHE Takes

The evidence does not justify withholding pain relief from an injured horse, and NHE would not suggest it. A horse in pain needs treatment, and that decision belongs to the attending veterinarian. What the evidence does justify is treating the 24 hour washout as standard practice rather than an afterthought. Schnabel's article states it directly: "A 24hour washout period is recommended after NSAID administration," and she lists sedation, anesthesia, surgery and intensive exercise as other reasons for the same pause before blood is collected for orthobiologic processing.

The NC State finding strengthens that advice for a specific reason. Penn's reassurance rests on a design that included the day off, and on phenylbutazone and firocoxib rather than a sustained course of flunixin. Owners should not stretch that reassurance to cover a horse that has been on flunixin twice a day all week and is bled between doses, particularly if the product is PRF. In that case, the useful question for the vet is simple: can the next dose wait until the blood has been drawn?

The research has a clear next step. A crossover trial testing multi-day flunixin in PRP and APS, with and without a washout, and following treated horses through to tendon and joint outcomes, would settle what the current papers can only point toward. Until it exists, the most useful thing a rider can bring to the conversation is the medication log.