Which of the following is a Xanthine drug?

A Xanthine drug is a member of a class of medications that includes theophylline and its derivatives, which are primarily used as bronchodilators in the treatment of respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD). These drugs act by relaxing the smooth muscles of the airways, thereby improving airflow and alleviating symptoms associated with bronchospasm.

Elixophyllin is specifically a brand name for a formulation of theophylline, reinforcing its classification as a Xanthine drug. It is effective in managing conditions where bronchodilation is necessary, showing its importance in respiratory therapy.

In contrast, Survanta and Curasurf are both surfactant preparations used in the management of neonatal respiratory distress syndrome, and Infasurf is also a surfactant medication. These medications serve a different purpose by reducing surface tension in the lungs to prevent atelectasis in premature infants, rather than providing bronchodilation like a Xanthine drug would. Thus, Elixophyllin stands out as the correct answer in this context.