Final answer:
A nurse should anticipate administering flumazenil to a client with a diazepam overdose, as it can reverse the potentially life-threatening effects of the overdose.
Step-by-step explanation:
In the case of a client who has taken large amounts of diazepam, a nurse in the emergency department should anticipate administering flumazenil. Flumazenil is an antagonist of the benzodiazepine receptors and is used to reverse the sedative effects of benzodiazepines, which can include potentially life-threatening overdoses. Its administration can quickly reverse the sedation and other effects caused by the overdose of diazepam, making it a critical intervention in an emergency setting.