Why are non-selective beta blockers avoided in asthmatics?

• A. They cause bronchoconstriction due to Beta-2 blockade
• B. They cause tachycardia
• C. They are ineffective in lowering blood pressure
• D. They cause liver toxicity

Answer: (A)

Non-selective beta blockers block both beta-1 receptors in the heart and beta-2 receptors in the lungs. In the airways, beta-2 receptor stimulation normally causes bronchodilation; blocking these receptors removes that relaxation, leading to bronchoconstriction. In asthmatics, whose airways are already prone to narrowing, this can trigger or worsen bronchospasm and dyspnea, which is why these drugs are avoided. Some beta blockers are cardioselective and primarily block beta-1, reducing heart effects with less impact on the lungs, but they’re still used with caution in asthma. Tachycardia would not explain avoidance, since beta blockers tend to slow heart rate, not cause it. They also aren’t primarily avoided for liver toxicity or general ineffectiveness in lowering blood pressure.