Which of the following can increase plasma levels of a TCA?

Cimetidine (Tagamet) is a medication that can increase plasma levels of tricyclic antidepressants (TCAs) through its effects on liver metabolism. Cimetidine is known to inhibit certain cytochrome P450 enzymes in the liver, particularly CYP2D6, which are essential for metabolizing various drugs, including TCAs. When these enzymes are inhibited, there is a decreased clearance of TCAs from the body, leading to higher plasma concentrations. This can potentially augment the therapeutic effects of TCAs but also increases the risk of adverse effects and toxicity.

In contrast, while antibiotics, antihistamines, and NSAIDs can interact with other medications, they do not significantly affect the metabolic pathways of TCAs in the same way that cimetidine does. Therefore, understanding the enzyme interactions and drug metabolism is crucial when considering how certain medications can impact plasma levels of TCAs.