Exercise-induced pulmonary haemorrhage in racing Thoroughbreds: does prerace furosemide vs saline reduce EIPH severity on endoscopy? — LIKELY

In racing Thoroughbreds, does prerace furosemide vs saline reduce the severity of exercise-induced pulmonary haemorrhage on endoscopy?

Shelf #816 · gate-verified and displayed under the developer's blinded-trial rule

LIKELY: This shelf's claim is EIPH severity and incidence on endoscopy - not mortality or any other hard outcome - so it is not Tier C. In Hinchcliff 2009, a randomized, placebo-controlled, blinded, crossover field trial in 167 Thoroughbred racehorses racing in South Africa, horses were substantially more likely to develop EIPH (score 1 or more; odds ratio 3.3 to 4.4 across analyses - a relative measure) or moderate to severe EIPH (score 2 or more; odds ratio 6.9 to 11.0, relative) after saline than after furosemide 500 mg intravenously, and 81 of 120 horses (67.5%) that had EIPH after saline had a reduction in EIPH severity score of at least 1 grade when treated with furosemide. The systematic review agrees: Sullivan 2015 found a pooled relative risk of detecting any EIPH after furosemide of 0.88 (95% CI 0.79-0.97; 11 studies, n = 5780), falling to 0.68 (95% CI 0.58-0.79) in the two high-quality randomised controlled trials (n = 405), with 68% of previously diagnosed horses improving by at least one grade (95% CI 61-78%). Timing matters: in Knych 2018 (15 Thoroughbreds, 3-way crossover), endoscopic scores were lower with furosemide at 4 hours than at 24 hours before exercise (P = 0.03), and bronchoalveolar lavage red cell counts were lower at 4 hours than with saline (P = 0.01) but did not differ between saline and 24-hour furosemide (P = 0.3). Design class (a): randomisation and blinding are both established by a carded record (Hinchcliff 2009: 'Randomized, placebo-controlled, blinded, crossover field trial', treatment order randomly determined). The honest limits: no treatment prevented EIPH outright, the all-studies pooled relative effect on detection is modest (relative risk 0.88), most of the wider literature is not high-quality randomised evidence, and the endpoint is an endoscopic grade - a severity measure, not survival or racing longevity. Drafted Nov 10, 2026 (VetMed build, topic #816); all figures from abstracts fetched and verified at drafting.

Hinchcliff 2009: Thoroughbreds were 3.3-4.4 times as likely (relative odds) to develop EIPH and 6.9-11.0 times as likely to develop moderate-severe EIPH after saline than after prerace furosemide; 67.5% of bleeders on saline improved by at least 1 grade on furosemide

Randomized, placebo-controlled, blinded, crossover field trial (record's own wording: 'Randomized, placebo-controlled, blinded, crossover field trial'; treatment order randomly determined)

Who: Horses: 167 Thoroughbred racehorses racing under typical racing conditions in South Africa, allocated to race fields of 9 to 16 horses and raced twice, 1 week apart, in the same field and over the same distance. Each horse received furosemide 500 mg intravenously before one race and placebo (saline solution) before the other, with the order of treatments randomly determined. EIPH severity was scored 0 to 4 by tracheobronchoscopy after each race.

Result: Horses were substantially more likely to develop EIPH (severity score 1 or more; odds ratio 3.3 to 4.4 across multivariable analyses - relative measures) or moderate to severe EIPH (severity score 2 or more; odds ratio 6.9 to 11.0, relative) following saline than following furosemide. In addition, 81 of the 120 horses (67.5%) that had EIPH after saline had a reduction in EIPH severity score of at least 1 when treated with furosemide. The authors conclude prerace furosemide decreased the incidence and severity of EIPH under typical racing conditions. The abstract reports odds ratios rather than per-treatment incidence percentages, so absolute EIPH rates by treatment cannot be quoted from this record.

Watch out: Odds ratios are relative measures and overstate risk ratios when the outcome is common, as EIPH is; the record gives no absolute incidence by arm. This is a crossover in one country's racing population with a single 500 mg intravenous dose - it establishes severity reduction under those conditions, not prevention of EIPH (most horses still bled) and not any effect on survival, career length or performance.

Hinchcliff KW, Morley PS, Guthrie AJ. Efficacy of furosemide for prevention of exercise-induced pulmonary hemorrhage in Thoroughbred racehorses. J Am Vet Med Assoc. 2009;235(1):76-82. PMID: 19566461. Registry ID: none in the record. MeSH: Animals · Diuretics/therapeutic use* · Female · Furosemide/therapeutic use* · Hemorrhage/prevention & control/veterinary* · Horse Diseases/drug therapy* · Horses · Lung Diseases/prevention & control/veterinary* · Male · Physical Conditioning, Animal/adverse effects*

Sullivan 2015: pooled relative risk of detecting EIPH after furosemide was 0.88 overall and 0.68 in the two high-quality randomised trials; 68% of previously diagnosed horses improved by at least one grade

Systematic review and meta-analysis (record's own wording: 'Systematic review with meta-analyses'; randomised controlled trials, nonrandomised trials and observational studies eligible)

Who: Horses: Thoroughbred and Standardbred racehorses in 17 studies meeting the inclusion criteria; the tracheobronchoscopy detection meta-analysis pooled 11 studies (n = 5780), and the high-quality randomised controlled trial analysis pooled 2 studies (n = 405) of horses previously diagnosed with EIPH for the grade-reduction analysis. EIPH was assessed by tracheobronchoscopy or by bronchoalveolar lavage fluid red blood cell number.

Result: The relative risk of detecting any EIPH by tracheobronchoscopy after furosemide was 0.88 (pooled data from 11 studies, n = 5780; 95% CI 0.79-0.97, P = 0.01) - a 12% relative reduction. Using only high-quality randomised controlled trials (2 studies, n = 405), the relative risk of detecting endoscopically evident EIPH was 0.68 (95% CI 0.58-0.79, P < 0.001) - a 32% relative reduction. The proportion of horses previously diagnosed with EIPH having a reduction of at least one EIPH grade after furosemide was 68% (2 studies, n = 405; 95% CI 61-78%). The authors conclude there is high-quality evidence, albeit limited, that furosemide reduces the incidence and severity of EIPH.

Watch out: The headline pooled relative risk (0.88) mixes study designs of varying quality and is a modest relative effect; the stronger 0.68 figure rests on only two randomised trials. Relative risks are printed as relative throughout this card; the review does not give a single absolute detection rate pair from which an absolute reduction could be stated here.

Sullivan SL, Whittem T, Morley PS, Hinchcliff KW. A systematic review and meta-analysis of the efficacy of furosemide for exercise-induced pulmonary haemorrhage in Thoroughbred and Standardbred racehorses. Equine Vet J. 2015;47(3):341-9. PMID: 25291214. Registry ID: none in the record. MeSH: Animals · Diuretics/therapeutic use · Furosemide/therapeutic use* · Hemorrhage/drug therapy/etiology/veterinary* · Horse Diseases/drug therapy* · Horses · Lung Diseases/drug therapy/etiology/veterinary* · Physical Conditioning, Animal/adverse effects*

Knych 2018: furosemide 4 hours before exercise gave lower endoscopic EIPH scores than furosemide at 24 hours (P = 0.03) and lower lavage red cell counts than saline (P = 0.01); 24-hour furosemide did not differ from saline on lavage counts (P = 0.3)

Randomised controlled trial, 3-way crossover (publication type: Randomized Controlled Trial; record's own wording: '3-way crossover'; blinding not stated in the record)

Who: Horses: 15 Thoroughbred racehorses in a 3-way crossover, receiving 5 mL of 0.9% saline or 250 mg furosemide either 4 or 24 hours before a 5-furlong simulated race. One hour post-race an endoscopic examination and bronchoalveolar lavage were performed; horses were assigned an EIPH score on predetermined criteria and red blood cells in lavage fluid were counted.

Result: Endoscopic EIPH scores were lower in the 4-hour furosemide group than the 24-hour group (P = 0.03). Red blood cell counts in lavage fluid were lower in the 4-hour furosemide group than the saline group (P = 0.01), with no difference between saline and 24-hour furosemide (P = 0.3) and none between the 4- and 24-hour groups on this measure (P = 0.5). No treatment prevented EIPH. The abstract gives P values without score or count values, so effect sizes cannot be stated from this record.

Watch out: Fifteen horses, a simulated (not pari-mutuel) race, and a wide range of running times, as the authors note. This card answers a timing question (4 hours vs 24 hours vs saline) in support of the main shelf question; its saline comparison rests on the lavage red cell count, not on a reported endoscopic-score difference versus saline.

Knych HK, Wilson WD, Vale A, Kass PH, Arthur RM, Jones JH. Effectiveness of furosemide in attenuating exercise-induced pulmonary haemorrhage in horses when administered at 4- and 24-h prior to high-speed training. Equine Vet J. 2018;50(3):350-355. PMID: 28963734. Registry ID: none in the record. MeSH: Animals · Bronchoalveolar Lavage Fluid · Cross-Over Studies · Diuretics/pharmacology · Female · Furosemide/pharmacology* · Hemorrhage/prevention & control/veterinary* · Horse Diseases/etiology*/prevention & control · Horses · Lung Diseases/etiology/prevention & control/veterinary* · Male · Physical Conditioning, Animal/adverse effects* · Physical Exertion · Running

Synthesis: prerace furosemide reduces EIPH incidence and endoscopic severity in racing Thoroughbreds - the randomised crossover trial and the meta-analysis of high-quality trials agree - LIKELY

Synthesis

Who: Synthesis of the cards above: Hinchcliff 2009 (167 Thoroughbred racehorses, randomized placebo-controlled blinded crossover field trial, South Africa), Sullivan 2015 (systematic review and meta-analysis, 17 studies; high-quality randomised subset 2 studies, n = 405) and Knych 2018 (15 Thoroughbreds, randomised 3-way crossover timing trial).

Result: (1) Severity: 67.5% of horses that bled after saline improved by at least 1 endoscopic grade on furosemide (Hinchcliff), and 68% (95% CI 61-78%) improved by at least one grade in the high-quality trials (Sullivan). (2) Incidence: relative risk of detecting EIPH 0.88 overall (95% CI 0.79-0.97) and 0.68 (95% CI 0.58-0.79) in high-quality randomised trials - both relative measures; saline-vs-furosemide odds ratios for moderate-severe EIPH were 6.9 to 11.0 in the crossover trial. (3) Timing: benefit is clearest at 4 hours before exercise; 24-hour administration did not separate from saline on lavage red cell counts.

Watch out: Furosemide attenuates EIPH; it does not prevent it, and nothing carded here addresses mortality, career longevity or the separate question of whether EIPH itself impairs performance. Standardbred evidence sits inside the Sullivan review; the primary randomised field trial carded here is in Thoroughbreds, matching this shelf's question.

Synthesis of Hinchcliff KW et al. PMID: 19566461; Sullivan SL et al. PMID: 25291214; Knych HK et al. PMID: 28963734. Registry IDs as on the individual cards.

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