Patients ordinarily should not be treated concomitantly with entacapone and a nonselective MAOI (entacapone can be used concomitantly with a selective MAO-B inhibitor (e.g. selegiline)). Concomitant use of entacapone and drugs known to be metabolized by COMT may result in increased heart rate, arrhythmias, and excessive changes in blood pressure. May cause orthostatic hypotension and syncope when administered with levodopa/carbidopa (use with caution in patients at risk of hypotension (such as those receiving antihypertensive drugs) or where transient hypotensive episodes would be poorly tolerated (cardiovascular disease or cerebrovascular disease)). Diarrhea might occur (use with caution in lower GI disease or increased risk of dehydration (severe diarrhea rarely occurs)). May cause hallucinations. Entacapone may potentiate the adverse dopaminergic effects of levodopa and may cause or exacerbate dyskinesias. Severe rhabdomyolysis reported rarely. Retroperitoneal fibrosis, pulmonary infiltrates, pleural effusion, and thickening of the pleura reported in a few patients treated with ergot-derivative dopamine receptor agonists (entacapone may induce similar pulmonary changes). Use with caution in biliary obstruction, and in hepatic impairment or severe renal impairment. Entacapone, in conjunction with other drug therapy which alters brain biogenic amine concentrations (e.g. MAOIs, SSRIs), has been associated with a syndrome resembling neuroleptic malignant syndrome (hyperpyrexia and confusion) on abrupt withdrawal or dosage reduction (avoid abrupt withdrawal of therapy).