What interaction occurs between cimetidine and theophylline?

The interaction between cimetidine and theophylline is significant due to cimetidine’s effect on drug metabolism. Cimetidine is known to inhibit certain cytochrome P450 enzymes, specifically CYP1A2 and CYP3A4, which play a crucial role in the metabolism of various drugs, including theophylline. When cimetidine is administered alongside theophylline, this inhibition leads to a decrease in the metabolism of theophylline, resulting in increased plasma levels of the drug.

This increase in theophylline exposure can lead to heightened therapeutic effects, but it also raises the risk of potential toxicity. Therefore, understanding this interaction is critical for adjusting dosages of theophylline when patients are placed on cimetidine, to avoid adverse effects associated with elevated drug levels.

Additionally, the choice indicating "no significant interaction" would be incorrect because it underestimates the clinical implications of administering these two drugs together. Hence, the correct understanding is that the presence of cimetidine indeed increases the exposure of theophylline, necessitating careful monitoring and possible adjustment of the dosage.