Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2021 Publisher: Cipla (EU) Limited, Dixcart House, Addlestone Road, Bourne Business Park, Addlestone, Surrey, KT15 2LE, United Kingdom
Pharmacotherapeutic group: Anticholinergics
ATC Code: R03BB01
Ipratropium bromide is a quaternary ammonium compound with anti-cholinergic (parasympatholytic) properties. In preclinical studies, it appears to inhibit vagally mediated reflexes by antagonising 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 ipratropium bromide is induced by local drug concentrations sufficient for anticholinergic efficacy at the bronchial smooth muscle and not by systemic drug concentrations.
In clinical trials using metered dose inhalers in patients with reversible bronchospasm associated with asthma or chronic obstructive pulmonary disease significant improvements in pulmonary function (FEV1 increases of 15% or more) occurred within 15 minutes, reached a peak in 1-2 hours, and persisted for approximately 4 hours.
Preclinical and clinical evidence suggest no deleterious effect of ipratropium bromide on airway mucous secretion, mucociliary clearance or gas exchange.
The therapeutic effect of ipratropium bromide 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 the lungs, depending on the formulation, device and inhalation technique. The major part of the dose is swallowed and passes through 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 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 contribute significantly to systemic exposure.
The drug is minimally (less than 20%) bound to plasma proteins. The quarternary amine of the ipratropium ion does not cross the blood-brain barrier.
Ipratropium has a mean total clearance of 2.3 L/min and a renal clearance of 0.9 L/min. After intravenous administration approximately 60% of the dose is metabolised, mainly by conjugation (40%), whereas after inhalation about 77% of the systemically available dose is metabolised by ester hydrolysis (41%) and conjugation (36%).
After inhalation of ipratropium bromide either with HFA 134a or CFC propellant, cumulative renal excretion over 24 hours was approximately 12% and l0%, respectively.
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 3.2 hours. The main urinary metabolites bind poorly to the muscarinic receptor and have to be regarded as ineffective.
The toxicity of ipratropium bromide has been investigated extensively in the following types of studies: acute, subchronic and chronic toxicity, carcinogenicity, reproductive toxicity and mutagenicity via oral, intravenous, subcutaneous, intranasal and/or inhalation routes. Based on these toxicity studies, the probability of systemic anticholinergic side effects decreases in the following order:
Intravenous > subcutaneous > oral > inhalation > intranasal.
Pre-clinically, ipratropium bromide was found to be well-tolerated. Two-year carcinogenicity studies in rats and mice have revealed no carcinogenic activity at doses up to approximately 1,200 times the maximum recommended human daily dose for intranasal ipratropium. Results of various mutagenicity tests were negative.
Studies to investigate the possible influence of ipratropium bromide on fertility, embryo-fetotoxicity, and peri-/postnatal development have been performed on mice, rats and rabbits. High oral levels, i.e. 1000 mg/kg/day in the rat and 125 mg/kg/day in the rabbit were maternotoxic for both species and embryo-/fetotoxic in the rat, where the fetal weight was reduced. Treatment-related malformations were not observed. The highest, technically feasible doses for inhalation of the pressurised inhalation, solution, 1.5 mg/kg/day (human equivalent dose of 0.24 mg/kg/day) in rats and 1.8 mg/kg/day (human equivalent dose of 0.576 mg/kg/day) in rabbits, showed no adverse effects on reproduction.
These doses are 6- and 14-fold the maximum recommended human daily dose (MRHDD) of 2 mg or 0.04 mg/kg (based on a body weight of 50 kg).
Preclinical data reveal no special hazard for humans based on conventional studies of safety pharmacology, repeated dose toxicity, genotoxicity, carcinogenic potential and toxicity to reproduction.
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