Canine idiopathic megaoesophagus: does sildenafil reduce regurgitation episodes? — POSSIBLE

POSSIBLE: Sildenafil reduced regurgitation episodes against placebo in both randomised trials, but the trials are tiny and study different populations, and the adult-dog trial's own authors judged the improvement not clinically relevant. Quintavalla 2017 (PMID: 28188161), a randomised controlled trial in 21 puppies with congenital idiopathic megaoesophagus, gave sildenafil oral suspension 1 mg/kg every 12 hours for 14 days or placebo in a masked fashion, with examiners unaware of the protocol: regurgitation episodes were 0.88 ± 1.40 on sildenafil vs 2.65 ± 1.56 on placebo (P < 0.0001), weight gain was 79.76 ± 28.30 per cent vs 53.40 ± 19.30 per cent (P = 0.034), and relative oesophageal diameter fell in the sildenafil group (0.97 ± 0.19 to 0.24 ± 0.14, P < 0.0001) but not in controls (0.98 ± 0.17 to 1.10 ± 0.25, P = 0.480). Mehain 2022 (PMID: 35066488), a randomized crossover study in 10 client-owned otherwise healthy adult dogs with stable generalised megaesophagus, gave compounded liquid sildenafil 1 mg/kg PO every 12 hours or placebo for 14 days each with a 7-day washout: regurgitation was a median 3.5 episodes/week on sildenafil (range 0 to 14.5) vs a median 4 episodes/week on placebo (range 0 to 28) and a median 6.5 episodes/week at baseline (range 1.5 to 19.5), a statistically significant reduction, but there were no differences in esophageal clearance times or quality-of-life scores and the authors conclude clinically relevant improvements were not seen. Design class (a): Quintavalla 2017 establishes randomisation and masked assessment, and Mehain 2022 establishes a randomized crossover order with double-blinding (MeSH: Double-Blind Method), each answering a sildenafil-vs-placebo comparison in dogs with megaesophagus. Narrowings stated on the face: (1) The mined question says 'vs standard management'; both trials randomised sildenafil vs placebo as an adjunct to standard management given to both arms — in Quintavalla an identical protocolised regimen (six small meals, elevated feeding, 10 minutes upright after each meal) in both groups, in Mehain each dog's established home feeding management continued unchanged through both crossover periods — so the trials answer sildenafil added to standard management vs standard management alone in substance; no trial randomised a management strategy itself; (2) Mehain 2022's full text reports that all 10 dogs underwent complete evaluation for an underlying cause and that 3 had congenital megaesophagus and 7 had idiopathic acquired megaesophagus — an idiopathic population, but adults (> 1 year) with generalised, mostly acquired disease, versus Quintavalla's congenital disease in puppies. The stamp is POSSIBLE rather than LIKELY because the total randomised evidence is 31 dogs, the populations differ (puppies with congenital disease vs adults with generalised disease), treatment lasted only 14 days in both trials, and the adult trial's effect on regurgitation (median 3.5 vs 4 episodes/week) was small in absolute terms. Near-misses, not carded: Winston 2023 (PMID: 36458673), a retrospective series of 13 dogs treated surgically (modified Heller myotomy and Dor fundoplication) for lower esophageal sphincter achalasia-like syndrome — a surgical question, not sildenafil, in which oral sildenafil was simply discontinued postoperatively; Tollefson 2022 (PMID: 35928120), a portal-vein ultrasound study in 13 dogs receiving sildenafil for pulmonary hypertension — no megaesophagus outcome; Reinero 2025 (PMID: 40589725), a single feline case report — wrong species and no comparison. Tier C adjudication, recorded on the face: Tier C is NOT engaged — no carded record makes a mortality or survival-primary benefit claim; regurgitation frequency, weight and oesophageal diameter are the outcomes throughout. Drafted Nov 10, 2026 (VetMed build, topic #414); figures from the abstracts and both full texts fetched and verified at drafting (the full texts govern where they differ from the abstracts; second-check corrections applied Nov 10, 2026).