Which adverse effect should be monitored in a client taking antihistamines for nausea?

Antihistamines are commonly used as antiemetic agents, particularly for nausea related to motion sickness or other vestibular disturbances. One of the notable adverse effects associated with certain antihistamines, especially first-generation ones like diphenhydramine or dimenhydrinate, is urinary retention. This occurs because these medications exert anticholinergic effects, which can lead to decreased bladder contractility and promote urinary retention.

Monitoring for urinary retention is crucial, particularly in clients who may already have underlying conditions that affect urinary function, such as prostatic hyperplasia in men or in individuals with neurogenic bladder issues. Recognizing and addressing urinary retention early can prevent complications and improve patient comfort.

The other options, while they may represent side effects associated with different drug classes or conditions, are not as closely linked with the common adverse effects seen with antihistamines in the context of nausea management. It's essential for healthcare providers to be vigilant about urinary retention when prescribing or administering antihistamines.