Increased rate of verteporfin uptake by the vascular endothelium with calcium channel blockers, polymyxin B or radiation therapy. Increased photosensitivity with photosensitizing agents (e.g. tetracyclines, sulfonamides, phenothiazines, sulfonylurea hypoglycaemic agents, thiazide diuretics and griseofulvin). Decreased verteporfin efficacy with compounds that quench active oxygen species or scavenge radicals e.g. dimethyl sulfoxide, betacarotene, ethanol, formate and mannitol. Decreased verteporfin efficacy with drugs that decrease clotting, vasoconstriction or platelet aggregation e.g. thromboxane A2 inhibitors. Anaesthetics may cause haemodynamic effects.