13G Filing: Rock Springs Capital Management and Ardelyx Inc. (ARDX)

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UNITED STATES

SECURITIES AND EXCHANGE
COMMISSION
Washington, DC 20549

 

SCHEDULE 13G

 

Under the Securities Exchange Act of 1934

(Amendment No. )*

Ardelyx, Inc.

(Name of Issuer)

Common Stock, par value, $0.0001 per share

(Title of Class of Securities)

039697107

(CUSIP Number)

October 23, 2017

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the
rule pursuant to which this Schedule is filed:

o Rule
13d-1(b)

x Rule
13d-1(c)

o Rule
13d-1(d)

*The remainder of this cover page shall be
filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for
any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of
this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934
(“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions
of the Act (however, see the Notes).