Final answer:
The most appropriate pharmacist recommendation is to decrease the dose of selegiline to 2.5 mg p.o. at breakfast and lunch.
Step-by-step explanation:
The most appropriate pharmacist recommendation for the 80-year-old patient receiving new orders for fluoxetine and selegiline is 2) Decrease the dose of selegiline to 2.5 mg p.o. at breakfast and lunch. Selegiline is an irreversible inhibitor of the enzyme monoamine oxidase-B (MAO-B), which is responsible for the metabolism of dopamine and other monoamines. Concurrent administration of selegiline with fluoxetine, a selective serotonin reuptake inhibitor (SSRI), can increase the risk of serotonin syndrome due to the increased levels of serotonin in the central nervous system. To reduce this risk, it is recommended to decrease the dose of selegiline and closely monitor the patient for symptoms of serotonin syndrome.