Mechanism of Action
The drug is a non-selective muscarinic antagonist that blocks $M_1$, $M_2$, and $M_3$ receptor subtypes. The primary therapeutic effect is achieved through the blockade of $M_3$ muscarinic receptors on bronchial smooth muscle, leading to relaxation. A key feature is the hydrophilicity of the molecule: due to the presence of a quaternary nitrogen atom, the drug penetrates biological membranes poorly, ensuring a predominantly local effect upon inhalation.
Pharmacological Effects
The main effect is bronchodilation, most pronounced in large and medium-sized bronchi. Unlike many other agents, ipratropium does not inhibit mucociliary clearance. However, the blockade of $M_3$ receptors in the mucosal glands leads to reduced secretion, which may increase sputum viscosity. Systemic effects with inhalation administration are virtually absent due to low absorption into the bloodstream.
Indications
Ipratropium bromide is a first-line drug in the treatment of COPD, as it effectively relieves the increased cholinergic influence of the vagus nerve on bronchial tone. It is also used in bronchial asthma and other obstructive airway diseases. In ENT practice, it is used to reduce rhinorrhea in vasomotor rhinitis.
Side Effects
Local side effects include dry mouth and increased sputum viscosity. Systemic atropine-like reactions (tachycardia, miosis, marked bronchospasm) practically do not occur with correct inhalation use. The risk of systemic action increases if the drug deposited in the oropharynx is swallowed.
Administration Guidelines
The standard dosage is 2 puffs (20 mcg each) 3–4 times daily. It is important to remember that during inhalation, only 10% of the substance reaches the small bronchi, while the rest settles in the oropharynx. To minimize systemic absorption, the pathway of drug elimination via mucociliary clearance should be considered, and swallowing should be avoided.