Imidazoline derivatives, such as xylometazoline, naphazoline, tetryzoline, tramazoline or oxymetazoline play an important pharmacological role as nasal drops in the symptomatic treatment of rhinitis. When comparing the toxicological data of these substances, it is noticeable that Oxymetazoline has an LD₅₀ value which is two orders of magnitude lower than all other imidazoline derivatives. Thus, ten vials of commercially available oxymetazoline nasal drops already contain a lethal amount. An explanation for this unusually high toxicity has not yet been found.