Moderate
Linezolid × Morphine
Oxazolidinone antibiotic×Natural opium alkaloids
Mechanism
Linezolid is a reversible MAO inhibitor and may mildly potentiate opioid CNS depression. Morphine does not cause serotonin syndrome directly (minimal serotonergic effect).
Symptoms
Sedation, fatigue, slowed reactions, impaired coordination. In older patients: fall and fracture risk. Driving and operating machinery: accident risk. Possible sedation increase and respiratory rate decrease.
Management
On the combination, do not raise morphine until linezolid ends (10–14 days). On a stable maintenance morphine dose (chronic pain, palliative care), adjustment is usually not needed. If marked sedation or bradypnoea develops, reduce morphine by 25%. Alternatives if available: fentanyl or hydromorphone (no serotonergic risk).