Increased risk of seizures & serotonin syndrome w/ MAOIs eg, phenelzine, tranylcypromine, linezolid. Reports of increased INR w/ warfarin. Tramadol: May increase plasma conc of tramadol w/ CYP2D6 inhibitors eg, quinidine, fluoxetine, paroxetine, amitriptyline, & bupropion. Increased plasma conc of tramadol & may result in greater amount of metabolism w/ CYP3A4 inhibitors eg, macrolides (eg, erythromycin), azole-antifungal agents (eg, ketoconazole), PIs (eg, ritonavir). Decreased plasma conc of tramadol w/ CYP3A4 inducers (eg, rifampin, carbamazepine, phenytoin). May produce additive CNS depressant effects (eg, profound sedation & resp depression) w/ benzodiazepines & other sedatives/hypnotics, tranquilizers, muscle relaxants, general anesth, other opioids, alcohol. Increased risk of adverse events including seizures & serotonin syndrome w/ serotonergic drugs eg, SSRIs, SNRIs, TCAs, triptans, 5-HT3 receptor antagonists, drugs that affect serotonin neurotransmitter system (eg, mirtazapine & trazadone), & some muscle relaxants (eg, cyclobenzaprine, metaxalone). Paracetamol: Reports of high anion gap metabolic acidosis from pyroglutamic acid (5-oxoprolinemia) w/ flucloxacillin.