The reason why theophylline is not so popular now is probably that there are many other safer and more effective choices.
New medications are coming on the market.
Particularly serevent, Long-acting Beta Agonist, has taken tha place of theophylline, because
it works in a similar way with theophylline; it works by relaxing the muscles around the airways in the lungs.
Also asthma medications are becoming more and more control-oriented, targetting chemical substances causing airway inflammation.
Singulair is an example of this. This is a leukotriene blocker.
Have you ever tried them?
If you continue to take theophylline, your blood level should be checked constantly.
Hope this would help.