Under the Securities Exchange Act of 1934
(Amendment No. 6)*

(Name of Company)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person
Authorized to Receive Notices and Communications)

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. o

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

* 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 disclosures provided in a prior cover page.

The information required on 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).

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Item 1.         Security and Company

This Amendment No. 6 (this “Schedule 13D/A”) amends the Schedule 13D originally dated May 6, 2009, as amended on July 28, 2009, November 25, 2009, December 20, 2010 and April 17, 2012, and as amended and restated in its entirety on July 9, 2012 and relates to the common stock, par value $0.001 per share (“Common Stock”), of Cornerstone Therapeutics Inc., a corporation organized under the laws of the State of Delaware (the “Company”).  The principal executive office of the Company is located at 1255 Crescent Green Drive, Suite 250, Cary, North Carolina 27518. Information given in response to each item below shall be deemed incorporated by reference in all other items below.

Item 2.         Identity and Background

Item 2 is hereby amended and restated in its entirety as follows:

(a) This Schedule 13D/A is being filed jointly on behalf of Chiesi Farmaceutici SpA (“Chiesi”) and Chiesi U.S. Corporation, a wholly-owned subsidiary of Chiesi (“Chiesi US”, and together with Chiesi, the “Filing Persons”).

(b) The principal business address and principal office address of Chiesi is Via Palermo 26/A, 43122 Parma, Italy.  The principal business address and principal office address of Chiesi US is c/o Chiesi Farmaceutici SpA, Via Palermo 26/A, 43122 Parma, Italy.

(c) Attached as Schedule A is the name, principal occupation, business address and citizenship of each executive officer and/or director of each of the Filing Persons.  Schedule A is incorporated into and made a part of this Schedule 13D/A.

(d) During the last five years, neither of the Filing Persons, nor any person listed on Schedule A has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e) During the last five years, neither of the Filing Persons, nor any person listed on Schedule A has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f) Chiesi is organized under the laws of Italy. Schedule A sets forth the citizenship of each executive officer and/or director of Chiesi.

Chiesi US is a corporation organized under the laws of the State of Delaware. Schedule A sets forth the citizenship of each executive officer and/or director of Chiesi US.

Item 3.         Source and Amount of Funds or Other Consideration

Item 3 is hereby amended to add the following:

In preparation for the Proposed Transaction (as defined in Item 4 below), on February 14, 2013, Chiesi transferred 15,687,538 of the shares of Common Stock beneficially owned by Chiesi to Chiesi US, a wholly-owned subsidiary of Chiesi.

The source of the consideration to be provided by Chiesi in connection with the Proposed Transaction will be working capital. No borrowed funds will be used in connection with the Proposed

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Transaction, other than any borrowed funds used for working capital purposes in the ordinary course of business.

Item 4.         Purpose of Transaction

Item 4 is hereby amended and restated in its entirety as follows:

On February 18, 2013, Chiesi delivered a letter (the “Letter”) to the Board of Directors of the Company (the “Board”) in which Chiesi proposed to acquire 100% of the Common Stock for a purchase price in the range of $6.40 to $6.70 per share in an all cash transaction (the “Proposed Transaction”).

As noted in the Letter, Chiesi has conducted an extensive review of the Company based on publically available information, Chiesi’s experience in the pharmaceutical industry and consultations with Chiesi’s advisors.  Based upon Chiesi’s experience and analysis, Chiesi believes the Company would be best positioned for long term growth and development as a private company and would benefit substantially from the synergies and shared resources that would result from this transaction with Chiesi.

The Proposed Transaction is subject to the grant by the Board of access to relevant non-public information regarding the Company, so that Chiesi can conduct due diligence.  Chiesi is prepared to move very quickly to enter into a customary confidentiality agreement with the Company and complete due diligence.

No binding obligation on the part of the Filing Persons or the Company will arise with respect to the Proposed Transaction as a result of the filing of this Schedule 13D/A or the delivery of the Letter.

The descriptions of the Letter and the Proposed Transaction above do not purport to be complete and are qualified in their entirety by reference to the Letter, a copy of which is filed as Exhibit 13 to this Schedule 13D/A and is incorporated herein by reference.

Other than as described above, neither the Filing Persons, nor to their knowledge, any of the individuals or entities named in Schedule A to this Schedule 13D/A, currently has any plan or proposal which relates to, or may result in, any of the matters listed in Items 4(a) — (i) of Schedule 13D/A (although they reserve the right to develop such plans).

Item 5.         Interest in Securities of the Company

Item 5 is hereby amended and restated in its entirety as follows:

(a) — (b) As of the date of this Schedule 13D/A, Chiesi beneficially owns 20,009,705 shares of Common Stock, representing approximately 65.0% of the Company’s issued and outstanding shares of Common Stock.  The 20,009,705 shares of Common Stock include: (a) 4,226,542 shares of Common Stock that are exercisable within 60 days, of which Chiesi will have sole power to vote and dispose, (b) 15,687,538 shares held by Chiesi US of which Chiesi may be deemed to share voting and dispositive power by virtue of its status as the sole stockholder of Chiesi US and (c) options to purchase 95,625 shares of Common Stock that are exercisable within 60 days of the date of this filing, held by certain directors of the Company, who are designees of Chiesi, and also serve as officers or directors of Chiesi, of which Chiesi may be deemed to possess shared power to vote and dispose.  As of the date of this Schedule 13D/A, Chiesi US beneficially owns 15,687,538 shares of Common Stock, representing approximately 59.3% of the Company’s issued and outstanding shares of Common Stock.  Chiesi US may be deemed to share voting and dispositive power in connection with the 15,687,538 shares of Common Stock with Chiesi by virtue of Chiesi US’s status as a wholly-owned subsidiary of Chiesi.  All calculations made in this

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paragraph were made in accordance with Rule 13d-3(d) of the Securities Exchange Act of 1934, as amended, and were calculated based on 26,440,902 shares of Common Stock outstanding as of November 1, 2012 (as reported in the Company’s 10-Q filed November 8, 2012).

To the knowledge of the Filing Persons and other than as set forth above, no other shares of Common Stock are beneficially owned by any of the individuals or entities named in Schedule A to this Schedule 13D.

(c) Neither of the Filing Persons, nor, to the knowledge of the Filing Persons, any of the individuals or entities named in Schedule A to this Schedule 13D, has effected any transaction in Common Stock during the past 60 days, except as disclosed herein.

(d) — (e) Not applicable.

Item 7.         Material to be Filed as Exhibits

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SIGNATURE

After reasonable inquiry and to the best of the knowledge and belief of the undersigned, the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: February 19, 2013

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SCHEDULE A

Chiesi Farmaceutici SpA

Directors

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Executive Officers (1)

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(1)         The listing of these individuals for purposes of this Schedule 13D shall not be deemed an admission that such individuals are “officers” under Italian law.

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Chiesi U.S. Corporation

Directors

Executive Officers

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