What can theophylline and phenytoin interact to cause?

• A. An increase in the seizure threshold
• B. A decrease in the seizure threshold
• C. No interaction
• D. Increased sedation

Answer: (B)

Theophylline and phenytoin can interact in such a way that leads to a decrease in the seizure threshold. Theophylline, primarily used as a bronchodilator in conditions like asthma or COPD, can have central nervous system stimulation effects. When used concurrently with phenytoin, an anticonvulsant medication, there is a risk that theophylline may potentiate the effects of phenytoin, resulting in increased chances of seizures due to the lowering of the seizure threshold.

This interaction occurs because theophylline can enhance metabolism of phenytoin, altering drug levels and potentially leading to subtherapeutic effects, thereby decreasing seizure control. Understanding this interaction is critical for clinicians when managing patients who may require both medications, to ensure they are monitoring for any neurological changes and adjusting dosages accordingly.