Ipratropium

Freely soluble

7.01e-04 g/L

Ipratropium is a short-acting agent that inhibits the parasympathetic nervous system at the level of the airway which then produces bronchodilatation. The effect of this agent starts after 1-2 hours and it is known to last only from 4 to 6 hours. As part of the effect, ipratropium relaxes the bronchial airways which reverse the narrowing that accounts for wheezy breathing, chest tightness, cough and abnormal gas exchange. In clinical trials where ipratropium was used in the initial management of status asthmaticus, it was demonstrated a clear benefit in pulmonary function in children and adults. However, the continuous use of ipratropium after an acute asthmatic attack is not proven to be significantly advantageous nor the prophylactic administration of this agent.

Ipratropium acts as an antagonist of the muscarinic acetylcholine receptor. This effect produces the inhibition of the parasympathetic nervous system in the airways and hence, inhibit their function. The function of the parasympathetic system in the airway is to generate bronchial secretions and constriction and hence, the inhibition of this action can lead to bronchodilation and fewer secretions. At the cellular level, the diameter of the airways is controlled by the release of acetylcholine into the muscle cells causing them to contract and producing a narrow airway. Thus administration of ipratropium stops the activity of acetylcholine in the smooth muscle preventing the contraction and producing relaxed airways.

Ipratropium is metabolized in the gastrointestinal tract by the activity of the cytochrome P-450 isoenzymes. From the orally administered dose, about 90% of the dose is excreted unchanged. The absorbed portion is partially metabolized by ester hydrolysis to inactive metabolites, tropic acid and tropane.