Equine asthma exacerbation: clenbuterol vs inhaled ipratropium for relief of bronchospasm — MAYBE (weak evidence)

STAMP: MAYBE (weak evidence): No eligible record exists for this shelf, and this pack is honestly empty (no cards). PubMed searches run at drafting (Nov 10, 2026) combining clenbuterol with ipratropium in horses returned no records at all, and broader searches for either drug with equine asthma, heaves, recurrent airway obstruction (RAO) or chronic obstructive pulmonary disease (COPD) found only single-drug studies — no study has ever compared clenbuterol against inhaled ipratropium head-to-head in horses, and no study reports a time-to-relief comparison between them, so which drug relieves bronchospasm faster cannot be answered from the published record. Near-misses, documented here and deliberately not carded because none answers this shelf's comparison: (1) Ipratropium alone — Robinson 1993 (PMID: 8354215) gave nebulised ipratropium bromide (25, 50 or 75 micrograms/ml, 4 ml/100 kg) or vehicle to 8 horses with RAO in a Williams square design, measuring lung function before and 1 and 4 hours after nebulisation: ipratropium decreased maximal pleural pressure change and pulmonary resistance and increased dynamic compliance, with a dose-dependent effect on resistance and compliance at 1 hour, and a separate experiment put its duration of action between 4 and 6 hours — but there was no clenbuterol arm. (2) Duvivier 1997 (PMID: 9308401) gave dry-powder ipratropium (600, 1200 and 2400 micrograms per horse) or placebo in randomised order to 6 horses with COPD: 1200 micrograms produced simultaneous decreased pulmonary resistance and increased dynamic compliance within 15 minutes, persisting for the 1-hour experiment — again, no clenbuterol comparator, and the 15-minute onset in this record cannot be set against any clenbuterol onset figure because no comparable clenbuterol time-course record exists. (3) Clenbuterol alone — Erichsen 1994 (PMID: 8575403), a field study of 239 horses with COPD given oral clenbuterol hydrochloride incrementally to effect (0.8 to 3.2 micrograms/kg twice daily), found clinical improvement in 75% of horses (lower 95% confidence limit 71%) assessed on treatment days 10 to 30 — a days-scale clinical study with no lung-function time course and no ipratropium arm, so it says nothing about speed of bronchospasm relief. (4) McGorum 2013 (PMID: 22850354) compared inhaled revatropate with inhaled ipratropium (positive control) and saline in 6 horses with heaves, finding the lowest doses of both drugs improved airway function within 1 hour — revatropate is a different anticholinergic, not clenbuterol, so this record homes nowhere on this shelf. (5) The remaining clenbuterol records (PMIDs: 16838204, 16624708) study anti-inflammatory effects after experimental challenge, not bronchodilator speed in exacerbation. Design class (c): randomisation is not established, because no eligible record answering this shelf's own comparison exists at all. One-home cross-points: inhaled corticosteroids vs systemic dexamethasone in equine asthma exacerbation homes on shelf #365, inhaled ciclesonide vs placebo is topic #814, and omega-3 supplementation in equine asthma homes on shelf #366 — corticosteroid and supplement questions, none of which carries a bronchodilator head-to-head claim, and none of whose figures are imported here. Tier C is not engaged (no mortality or survival claim). Drafted Nov 10, 2026 (VetMed build, topic #815); figures from the abstracts, fetched and verified at drafting.