ZK-90055 hydrochloride is a β2 adrenergic receptor agonist.
Contrasting a pro-drug, a soft-drug is active per se when given locally but is rapidly inactivated when it reaches the general circulation. Thus, a long duration of action at a minimum of systemic side effects may be achieved after inhalation of a h2-agonist designed in this way. One such example is ZK-90055, an indol derivative with a hydrolysable ester bond on the ring system. The development of ZK-90055 is stopped before clinical trials are commenced[2].
[1]. Waldeck B, et al. beta-Adrenoceptor agonists after terbutaline. Pharmacol Toxicol. 1995;77 Suppl 3:25-9. [2]. Waldeck B, et al. Beta-adrenoceptor agonists and asthma--100 years of development. Eur J Pharmacol. 2002 Jun 7;445(1-2):1-12.