Final answer:
The statement in the question is false. Xanthines have been used in asthma therapy for many years due to their bronchodilator effects, but they are not being replaced by beta agonists.
Step-by-step explanation:
The statement in the question is false. Xanthines, such as theophylline, have been used in asthma therapy for many years due to their bronchodilator effects. They work by relaxing the smooth muscles of the airways, opening them wider and making it easier to breathe. Beta agonists, on the other hand, are a different class of drugs that also help to open the airways, but they work by stimulating beta-2 adrenergic receptors in the smooth muscles, causing them to relax. These medications are commonly used in the treatment of asthma because they provide quick relief of symptoms and are more selective in their action.