Intravenous and intratracheal administration of trimetoquinol, a fast-acting short-lived bronchodilator in horses with 'heaves'.
Authors: Camargo F C, Robinson N E, Berney C, Eberhart S, Baker S, DeTolve P, Derksen F J, Harkins J D, Lehner A F, Tobin T
Journal: Equine veterinary journal
Summary
# Editorial Summary: Trimetoquinol as a Bronchodilator in Equine Heaves Researchers evaluated trimetoquinol (TMQ), a potent beta-adrenergic agonist established in human medicine, to determine whether it might offer therapeutic benefit for horses with recurrent airway obstruction (heaves). Using dose-escalation protocols, they administered TMQ intravenously (0.001–0.2 µg/kg) and intratracheally (0.01–2 µg/kg) to affected horses, measuring bronchodilation via changes in pleural pressure and monitoring cardiovascular effects through heart rate alongside subjective scoring of side effects. TMQ demonstrated remarkable potency as a cardiac stimulant, with heart rate elevation occurring at doses as low as 0.01 µg/kg intravenously and continuing to increase at maximal dosing; bronchodilation began at the same threshold but proved more modest, whilst intratracheal administration proved 50–100-fold less potent systemically, though side effects (sweating, agitation, muscle trembling) occurred via both routes. Both effects developed rapidly within 3 minutes but dissipated completely within 2 hours, making the drug unsuitable for sustained therapeutic control via these routes. Whilst TMQ's speed of action suggests potential as a rescue agent during acute episodes, the pronounced cardiac stimulation and undesirable side effects encountered via intravenous and intratracheal administration argue against clinical adoption by these routes; however, alternative delivery methods—particularly aerosol inhalation or oral formulations—warrant investigation as safer means of achieving localised bronchodilation without systemic cardiovascular complications.
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Practical Takeaways
- •TMQ by i.v. and i.t. routes is unsuitable for clinical use in heaves due to potent and unpredictable cardiac stimulation and short duration requiring frequent dosing
- •TMQ shows promise as a potential rescue bronchodilator during acute heaves episodes if alternative routes (aerosol or oral) can be developed with safer cardiac profiles
- •Current beta-agonist options by i.v./i.t. routes remain preferred pending further investigation of TMQ by other administration routes
Key Findings
- •Intravenous TMQ was exceptionally potent as a cardiac stimulant, increasing heart rate at doses as low as 0.01 microg/kg bwt
- •Airway bronchodilation commenced at 0.01 microg/kg bwt i.v. with rapid onset within 3 minutes but effects ceased by 2 hours
- •Intratracheal TMQ was 50-100-fold less potent than i.v. administration
- •Side effects including sweating, agitation and muscle trembling accompanied both routes of administration