Docopa 400 mg is a bronchodilator containing Doxofylline, a methylxanthine derivative. It is structurally related to theophylline but has a better safety profile due to its selective inhibition of phosphodiesterase-4 (PDE4) and lower affinity for adenosine receptors. This leads to relaxation of bronchial smooth muscles, making it effective in managing respiratory conditions like asthma and chronic obstructive pulmonary disease (COPD).