<prompt> DOC for acute attack of asthma in patients on Beta blockersSalbutamolTheophyllineIpratropium bomideChlorpheniramine  <response>: Respiratory airway has beta adrenergic receptorsbeta 2 receptors. Beta 2 agonists cause bronchodilatation, and beta 2 blockers cause bronchoconstriction. ipratropium bromide:- Atropine like drugs cause bronchodilatation by blocking M3 receptor mediated cholinergic constrictor tone; act primarily in the larger airways which receive vagal innervation. Ipratropium bromideis a sho acting duration 4-6 hours inhaled anticholinergic bronchodilator, while tiotropium bromide is long acting duration 24 hours. They are the bronchodilators of choice in COPD. Ref:- kd tripathi;pg num:- 227,228 