AstraZeneca Plc (AZN - Get Report) said Friday that it had received a second "complete response letter" from the U.S. Food & Drug Administration regarding its ZS-9 Hyperkalaemia treatment, putting the drug's approval process in the United States in doubt.

AstraZeneca had its first application for its ZS-9 treatment rejected by the FDA in May of last year after an inspection of its manufacturing facilities, but the company resubmitted its proposal in October. AstraZeneca acquired the rights to ZS-9, which it describes as a "potential best-in-class treatment for hyperkalaemia", or elevated levels of potassium in the blood, in the $2.7 billion takeover of ZS Pharma (ZSPH) in December 2015. 

"AstraZeneca and ZS Pharma are committed to working with the FDA to resolve the remaining matters under review as soon as possible," the company said in a statement.

AstraZeneca shares were marked 0.5% lower at 4,840.77 pence each by 09:15 GMT in London Thursday, trimming the three month gain to around 10% compared to a 6.1% advance for the Stoxx Europe 600 Health Care Index.

Shares in Swiss-based Galencia AG  (GGAL - Get Report) , however, traded 1.7% higher in Zurich to change hands at Sfr1,194 each, valuing the company at Sfr7.7 billion ($7.7 billion).

Galencia purchased Redwood City, California-based Relypsa Inc. (RLYP) last year for around $1.5 billion in part to gain access to its Veltassa Hyperkalaemia treatment, which analysts have said could soon reach $1.4 billion in annual sales.