A client is taking oxybutynin for overactive bladder and haloperidol (Haldol) for antipsychotic treatment. What possible side effect should the nurse monitor for due to the interaction of these medications?

A. Hypotension: Hypotension is not a common interaction between oxybutynin and haloperidol. B. Lowered plasma concentrations: There is no significant interaction that would lead to lowered plasma concentrations of either medication. C. Increased effect of the antispasmodic drug: Both oxybutynin and haloperidol have anticholinergic properties. When combined, these properties can increase the risk of anticholinergic side effects, such as dry mouth, constipation, and urinary retention, enhancing the effect of oxybutynin. D. Decreased effect of the antipsychotic drug: There is no evidence that oxybutynin would decrease the effect of haloperidol.