Clinical meaning
Anticholinergic bronchodilators block muscarinic (M) receptors on airway smooth muscle. Three subtypes are clinically relevant: M1 (ganglionic, facilitates neurotransmission), M2 (presynaptic, inhibits ACh release - negative feedback), and M3 (postsynaptic smooth muscle, mediates bronchoconstriction and mucus secretion). Ideal anticholinergic bronchodilators selectively block M3 and M1 while sparing M2 to prevent paradoxical ACh release. Short-acting muscarinic antagonists (SAMAs) like ipratropium block all three subtypes non-selectively with 6-8 hour duration. Long-acting muscarinic antagonists (LAMAs) like tiotropium have kinetic selectivity: slow dissociation from M3 (dwell time > 24 hours) but rapid dissociation from M2, providing functional M3 selectivity and once-daily dosing. LAMAs are first-line maintenance bronchodilators for COPD, reducing exacerbations and improving lung function.
Diagnosis & workup
Diagnostics & workup: - Assess anticholinergic burden using validated scales (ACB scale) - Monitor heart rate and rhythm during initiation - Assess urinary symptoms before prescribing (IPSS score in males) - Measure intraocular pressure if glaucoma risk - Cognitive screening in elderly patients (MoCA) - Spirometry to confirm bronchodilator response