Effect of isoproterenol on measured theophylline levels.

Aggressive pharmacotherapy for the treatment of patients with severe status asthmaticus includes theophylline and beta-adrenergic agonists such as isoproterenol. We found that the measured theophylline level decreased when an isoproterenol infusion was started, and this decrease persisted throughout the entire exposure to isoproterenol. When the isoproterenol infusion was discontinued, the theophylline level increased. The etiology of this observed effect is unknown.