Pharmacotherapeutic group: Anticholinergics. ATC Code: R03BB01.
Pharmacology: ATROVENT (ipratropium bromide) is a quaternary ammonium compound with anticholinergic (parasympatholytic) properties. In nonclinical studies, it appears to inhibit vagally mediated reflexes by antagonizing the action of acetylcholine, the transmitter agent released from the vagus nerve. Anticholinergics prevent the increase in intracellular concentration of Ca++ which is caused by interaction of acetylcholine with the muscarinic receptor on bronchial smooth muscle.
Ca++ release is mediated by the second messenger system consisting of IP3 (inositol triphosphate) and DAG (diacylglycerol).
The bronchodilation following inhalation of ATROVENT (ipratropium bromide) is primarily local and site specific to the lung and not systemic in nature.
Preclinical and clinical evidence suggest no deleterious effect of ATROVENT (ipratropium bromide) on airway mucous secretion, mucociliary clearance or gas exchange.
Clinical trials: Metered Dose Inhaler/Solution for inhalation: Trials with a treatment duration of up to three months involving adult asthmatics and COPD patients, and asthmatic children, in which the CFC-free formulation and the CFC formulation have been compared have shown the two formulations to be therapeutically equivalent.
In controlled 90 day studies in patients with bronchospasm associated with chronic obstructive pulmonary disease (chronic bronchitis and emphysema) significant improvements in pulmonary function occurred within 15 minutes, reached a peak in 1-2 hours, and persisted for up to 4 - 6 hours.
In controlled 90 day studies in patients with bronchospasm associated with asthma, significant improvements in pulmonary function (FEV1 increases of 15%) occurred in 51% of the patients.
Pharmacokinetics: Absorption: The therapeutic effect of ATROVENT is produced by a local action in the airways. Time courses of bronchodilation and systemic pharmacokinetics do not run in parallel.
Following inhalation 10 to 30% of a dose is generally deposited in lungs, depending on the formulation and inhalation technique. The major part of the dose is swallowed and passes the gastro-intestinal tract.
The portion of the dose deposited in the lungs reaches the circulation rapidly (within minutes).
Cumulative renal excretion (0-24 hrs) of the parent compound is approximated to 46% of an intravenously administered dose, below 1% of an oral dose and approximately 3 to 13% of an inhaled dose. Based on these data the total systemic bioavailability of oral and inhaled doses of ipratropium bromide is estimated at 2% and 7 to 28%, respectively.
Taking this into account, swallowed dose portions of ipratropium bromide do not relevantly contribute to systemic exposure.
Distribution: Kinetic parameters describing the disposition of ipratropium were calculated from plasma concentrations after i.v. administration. A rapid biphasic decline in plasma concentrations is observed. The apparent volume of distribution at steady-state (Vdss) is approximately 176 L (≈ 2.4 L/kg). The drug is minimally (less than 20%) bound to plasma proteins. Nonclinical data indicate that quaternary amine ipratropium does not cross the placental or the blood-brain barrier.
Biotransformation: After intravenous administration approximately 60% of a dose is metabolised, the major portion probably in the liver by oxidation.
The known metabolites, which are formed by hydrolysis, dehydration or elimination of the hydroxy-methyl group in the tropic acid moiety, show very little or no affinity for the muscarinic receptor and have to be regarded as ineffective.
Elimination: The half-life of the terminal elimination phase is approximately 1.6 hours.
Ipratropium has a total clearance of 2.3 L/min and a renal clearance of 0.9 L/min.
In an excretion balance study cumulative renal excretion (6 days) of drug-related radioactivity (including parent compound and all metabolites) accounted for 72.1% after intravenous administration, 9.3% after oral administration and 3.2% after inhalation. Total radioactivity excreted via the faeces was 6.3% following intravenous application, 88.5% following oral dosing and 69.4% after inhalation. Regarding the excretion of drug-related radioactivity after intravenous administration, the main excretion occurs via the kidneys. The half-life for elimination of drug-related radioactivity (parent compound and metabolites) is 3.6 hours.