This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Mechanism of action of timolol is ? 
Select and explain. 
A. Nonselective beta blocker, B. Nonselective alpha blocker, C. Selective beta 1 blocker, D. Selective beta 2 blocker
A: Nonselective beta blocker
Answer: A: Nonselective beta blocker 
Explanation: Ans. is 'a' i.e., Nonselective beta blocker Timolol is a non selective beta blocker (betal + beta 2). Thus when it is used in the treatment of glaucoma it can precipitate an attack of asthma by blocking beta 2 receptors.