May precipitate w/drawal syndrome w/ opioid agonists/antagonists (eg, buprenorphine, nalbuphine, pentazocine). Tramadol: May increase plasma conc of tramadol & decrease plasma conc of M1 w/ CYP2D6 inhibitors (eg, quinidine, fluoxetine, paroxetine, amitriptyline & bupropion). May increase plasma conc w/ CYP3A4 inhibitors [eg, macrolide antibiotics (eg, erythromycin), azole-antifungal agents (eg, ketoconazole), PIs (eg, ritonavir)]. May decrease plasma conc w/ CYP3A4 inducers (eg, rifampin, carbamazepine, phenytoin). May produce additive CNS depressant effects (eg, profound sedation & resp depression) w/ CNS depressants (eg, benzodiazepines & other sedatives/hypnotics, anesth agents, phenothiazines, tranquilizers, opioids or alcohol). Increased risk of seizures & serotonin syndrome w/ serotonergic drugs [eg, SSRIs, SNRIs, TCAs, triptans, 5-HT3 receptor antagonists, drugs that affect serotonin neurotransmitter system (eg, mirtazapine & trazodone) & some muscle relaxants (eg, cyclobenzaprine, metaxalone)]; MAOIs or use w/in 14 days of discontinuation. Possible alteration of warfarin effect including elevation of prothrombin time. Possible digoxin toxicity. Paracetamol: May produce hypoprothrombinemia w/ warfarin-like compd. Increased plasma levels w/ diflunisal. Possible high anion gap metabolic acidosis w/ flucloxacillin.