While BPH rarely causes sudden urinary retention, the condition can become acute in the presence of certain medications (blood pressure pills, anti histamines, antiparkinson medications), after spinal anaesthesia or stroke.

Istradefylline reduces dyskinesia resulting from long-term treatment with classical antiparkinson drugs such as levodopa.

Interactions with other anticholinergics like tricyclic antidepressants, antiparkinson drugs and quinidine, which theoretically increase side effects, are clinically irrelevant when ipratropium is administered as an inhalant.