Severe, prolonged HTN & possible arrhythmias w/ volatile halogenated anesth agents, MAOIs, TCAs, linezolid, adrenergic-serotoninergic drugs or other cardiac sensitizing agents. Enhanced effects by guanethidine. Incompatibility w/ Fe salts, alkalis, oxidising agents, barbiturates, chlorpheniramine, chlorothiazide, nitrofurantoin, phenytoin, Na bicarbonate, Na iodide, streptomycin, sulfadiazine, sulfafurazole, insulin.