A nurse is caring for a client who started the SSRI fluoxetine 3 days ago and now reports feeling agitated, with muscle tremors and a temperature of 39°C (102.2°F). Upon assessment, the nurse notes hyperreflexia, tremors, and diaphoresis. What is the nurse's best initial action?

A. Administer acetaminophen for the fever and continue to monitor the client: Fever associated with serotonin syndrome is caused by neuromuscular hyperactivity, not infection or inflammation. Acetaminophen will not correct the underlying cause and delays definitive treatment. Immediate escalation of care is required. B. Increase the client's fluid intake to prevent dehydration and recheck vital signs in one hour: Hydration alone is insufficient in the presence of agitation, hyperreflexia, tremors, and hyperthermia. Waiting an hour risks rapid clinical deterioration. These findings require urgent medical intervention, not delayed reassessment. C. Notify the provider immediately to evaluate for serotonin syndrome and initiate treatment: Recent initiation of fluoxetine combined with hyperthermia, agitation, hyperreflexia, tremors, and diaphoresis strongly suggests serotonin syndrome. This is a medical emergency requiring immediate discontinuation of serotonergic agents and supportive or pharmacologic treatment. D. Encourage the client to rest and provide a cooling blanket to reduce the fever: Cooling measures may be part of supportive management but are not sufficient as an initial nursing response. Without provider notification and treatment, symptoms may progress to seizures, arrhythmias, or death.