Registration Rights Agreement Joinder with respect to the Registration Rights Agreement for Sky Growth Acquisition Corporation $490,000,0007 3/8% Senior Notes due 2020

Exhibit 4.5

Registration Rights Agreement Joinder

with respect to the

Registration Rights Agreement

for

Sky Growth Acquisition Corporation

$490,000,000 7 ³/₈% Senior Notes due 2020

September 28, 2012

Goldman, Sachs & Co.,

As representative of the several Purchasers

named in Schedule A hereto (the “Purchasers”)

c/o Goldman, Sachs & Co.

200 West Street,

New York, New York 10282

Ladies and Gentlemen:

Reference is hereby made to that certain Registration Rights Agreement, dated as of September 28, 2012 (the “Registration Rights Agreement”), between Sky Growth Acquisition Corporation, a Delaware corporation, and Goldman, Sachs & Co., as representative of the Purchasers, providing for the issuance and sale of the Securities (as defined therein). As a condition to the consummation of the offering of the Securities, in the event that the Merger Date occurs at the Time of Delivery (as defined in the Purchase Agreement referenced in the Registration Rights Agreement), each of Par Pharmaceutical Companies, Inc., a Delaware corporation (the “Company”), and each Guarantor (as defined in the Registration Rights Agreement) has agreed to join in the Registration Rights Agreement as of the date hereof. Unless otherwise defined herein, capitalized terms used but not defined herein shall have the respective meanings given them in the Registration Rights Agreement.

The Company and each Guarantor hereby agrees for the benefit of the Purchasers, as follows:

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Schedule A

Goldman, Sachs & Co.

Merrill Lynch, Pierce, Fenner & Smith Incorporated

Deutsche Bank Securities Inc.

Citigroup Global Markets Inc.

RBC Capital Markets, LLC

BMO Capital Markets Corp.