Which medication can interact with TCAs and increase its plasma level?

Cimetidine, commonly known by its brand name Tagamet, is a medication that can increase the plasma levels of tricyclic antidepressants (TCAs). The reason for this interaction lies in Cimetidine's ability to inhibit certain liver enzymes, particularly cytochrome P450 enzymes, that are responsible for metabolizing TCAs. When these enzymes are inhibited, the clearance of TCAs from the body is reduced, leading to higher plasma concentrations. This can potentially enhance the effects of TCAs and increase the risk of side effects, including toxicity.

The other medications listed do not have the same significant interaction with TCAs. For instance, ibuprofen is a non-steroidal anti-inflammatory drug (NSAID) primarily used for pain and inflammation and does not notably alter TCA metabolism. Amoxicillin, an antibiotic, is unlikely to affect TCA levels as they do not share metabolic pathways that would lead to interaction. Propranolol, a beta-blocker, can also influence metabolism but is not known to have a substantial effect on TCA plasma levels in the same way that Cimetidine does. Thus, Cimetidine is the medication most clearly associated with an increase in TCA plasma levels.