Ipratropium bromide is an anticholinergic (parasympatholytic) agent that, based on animal studies, appears to inhibit vagally mediated reflexes by antagonizing the action of acetylcholine, the transmitter agent released from the vagus nerve.

Anticholinergics prevent the increases in intracellular concentration of cyclic guanosine monophosphate (cyclic GMP) that are caused by interaction of acetylcholine with the muscarinic receptor on bronchial smooth muscle.

The bronchodilation following inhalation of ipratropium bromide is primarily a local, site-specific effect, not a systemic one. Much of an administered dose is swallowed but not absorbed, as shown by fecal excretion studies. Following nebulization of a 2 mg dose, a mean 7% of the dose was absorbed into the systemic circulation either from the surface of the lung or from the gastrointestinal tract. The half-life of elimination is about 1.6 hours after intravenous administration. Ipratropium bromide is minimally (0 to 9% in vitro) bound to plasma albumin and a 1-acid glycoproteins. It is partially metabolized. Autoradiographic studies in rats have shown that ipratropium bromide does not penetrate the blood-brain barrier. Ipratropium bromide has not been studied in patients with hepatic or renal insufficiency. It should be used with caution in those patient populations.

In controlled 12-week studies in patients with bronchospasm associated with chronic obstructive pulmonary disease (chronic bronchitis and emphysema) significant improvements in pulmonary function (FEV 1 increases of 15% or more) occurred within 15 to 30 minutes, reached a peak in 1 to 2 hours, and persisted for periods of 4 to 5 hours in the majority of patients, with about 25% to 38% of the patients demonstrating increases of 15% or more for at least 7 to 8 hours. Continued effectiveness of ipratropium bromide inhalation solution was demonstrated throughout the 12-week period. In addition, significant increases in forced vital capacity (FVC) have been demonstrated. However, ipratropium bromide did not consistently produce significant improvement in subjective symptom scores nor in quality of life scores over the 12-week duration of study.

Additional controlled 12-week studies were conducted to evaluate the safety and effectiveness of ipratropium bromide inhalation solution administered concomitantly with the beta adrenergic bronchodilator solutions metaproterenol and albuterol compared with the administration of each of the beta agonists alone. Combined therapy produced significant additional improvement in FEV 1 and FVC. On combined therapy, the median duration of 15% improvement in FEV 1 was 5 to 7 hours, compared with 3 to 4 hours in patients receiving a beta agonist alone.