Increased plasma conc w/ CYP3A4 inhibitors eg, macrolides (eg, erythromycin), azole-antifungal agents (eg, ketoconazole), PIs (eg, ritonavir). Decreased plasma conc w/ CYP3A4 inducers eg, rifampin, carbamazepine, phenytoin. Additive CNS depressant effects w/ CNS depressants eg, benzodiazepines & other sedatives/hypnotics, anesth agents, phenothiazines, tranquilizers, opioids or alcohol. Serotonin syndrome w/ serotonergic drugs. Increased risk of seizures & serotonin syndrome w/ MAOIs eg, phenelzine, tranylcypromine, linezolid. High anion gap metabolic acidosis from pyroglutamic acid w/ flucloxacillin. Increased INR w/ warfarin. Inhibition of tramadol metabolism w/ CYP2D6 inhibitors eg, quinidine, fluoxetine, paroxetine, amitriptyline, bupropion.