Oxybutynin R-isomer , also known as Aroxybutynin, is a muscarinic receptor antagonist. Aroxybutynin is the optically avtice inhibitor of proliferation and supresses gene expression in bladder smooth muscle cells. Oxybutynin exerts direct antispasmodic effect on smooth muscle and inhibits the muscarinic action of acetylcholine on smooth muscle. It exhibits one-fifth of the anticholinergic activity of atropine on the rabbit detrusor muscle, but four to ten times the antispasmodic activity. No blocking effects occur at skeletal neuromuscular junctions or autonomic ganglia (antinicotinic effects).