Mr Lee, a 68-year-old taxi driver, had chronic obstructive pulmonary disease ("COPD”) with a chronic cough producing thick sputum, breathlessness and exercise limitation. The cough and sputum production have not changed recently. He stopped smoking for 3 months previously because of his dyspnea. Prior to his smoking cessation, he has been smoking 20 cigarettes a day for 50 years. He had no other significant medical illnesses. His forced expiratory volume in one second ("FEV1") was 1.34 L (about 45% of predicted). He was given the combination of ipratropium and salbutamol via a pressurized metered dose inhaler ("pMDI") for symptomatic relief. A trial of inhaled budesonide given 3 months previously provided no benefit and it has been stopped now. 

(a) Which classes of drugs do ipratropium and salbutamol belong to? (2 marks) 

Ipratropium is an anti-muscarinic (short acting muscarinic antagonist SAMA).

Salbutamol is a short acting beta-2 receptor agonist (SABA).

They are both bronchodilators.

(b) Describe the mechanisms of action for ipratropium and salbutamol. (6 marks) 

Ipratropium 

MOA: The sympathetic nervous system is opposed by the parasympathetic nervous system. Stimulation by acetylcholine on the muscarinic receptors in the airways causes bronchoconstriction. Anti-muscarinic agents blocks parasympathetic activity inducing bronchodilation.

Salbutamol

MOA: Activation of the beta-2 adrenergic receptors in the airways.

Beta adrenoceptors are activated by the sympathetic nervous system in the fight or flight response which causes bronchodilation to increase lung function.