Exhibit 10.1  MUTUAL TERMINATION AGREEMENT  WHEREAS,
Glaxo Group Limited, a company organized under the laws of England &
Wales and having its principal place of business at Glaxo Wellcome House,
Berkeley Avenue, Greenford, Middlesex, UB6 ONN, United Kingdom (GSK) and
Sepracor Inc., a company organized under the laws of the State of Delaware,
United States, and having its principal place of business at 84 Waterford
Drive, Marlborough, MA 01752-7010 are parties to a Development, License and
Commercialization Agreement dated September 11, 2007 (the License
Agreement);  AND
WHEREAS, both GSK and Sepracor now wish to terminate such License Agreement on
the following terms and conditions;  THEREFORE,
GSK and Sepracor agree with effect from the last date written below (the Termination
Effective Date) as follows:  1.             Definitions.Unless defined specifically herein, all
capitalized terms shall have the meaning contained in the License Agreement.  2.             Mutual Termination.GSK and Sepracor hereby
agree to terminate the License Agreement under Section 14.2(a) (by
mutual written agreement of the parties) for the entire GSK Territory.  All rights granted by Sepracor to GSK in the
Product shall cease on the Termination Effective Date, except as otherwise set
forth below.  3.             Developmental Studies.With respect to theResidual Effects Study,
ESZ111503, GSK shall provide to Sepracor a copy of the de-identified clinical
data within thirty (30) days from the Termination Effective Date and shall
continue to make any other information from the study available to Sepracor
upon reasonable request in a manner consistent with applicable laws and
regulations.  4.             Confirmations and Other Items.  a.Other than as
set forth in this Mutual Termination Agreement, GSK and Sepracor confirm that
each party is current in its payments due to the other and that no further
payments, milestones or other consideration are due to either party under the
terms of the License Agreement.  The
parties may submit to one another any reimbursement of nominal expenses agreed
upon during the course of work under the License Agreement (not to exceed
$50,000 in the aggregate) for up to ninety (90) days after the Termination
Effective Date.  1


b.GSK shall procure
that the recipients of any letters of authorization issued for national
entities within the EU for registration and/or pricing purposes will be
notified within twenty (20) business days of the Termination Effective Date
that such letters have been nullified, and provide Sepracor with copies of such
letters of notification.  Further GSK
shall use its reasonable endeavours to return to Sepracor within twenty (20)
business days of the Termination Effective Date all such letters of
authorization that are still within the control of GSK and its affiliated
companies.  c.GSK will
maintain the alliance document portal and continue to make it available to
Sepracor for no less than ten (10) business days after the Termination
Effective Date so that Sepracor may download and retain documents from the
site.  5.             Surviving Terms.While all terms of the License Agreement surviving
under Section 15.5 shall continue to survive, the Parties hereby release
one another, their respective directors, officers, employees, Affiliates,
successors and assigns from any other liability under the License Agreement
except as may be described in this Mutual Termination Agreement.  2


IN WITNESS WHEREOF, Sepracor Inc. and Glaxo Group Limited
have executed this Mutual Termination Agreement as of the Termination Effective
Date.  Sepracor Inc.  BY:
  /s/ Adrian Adams
  
  Date:
  29thApril 2009NAME:
  Adrian AdamsTITLE:
  President &
  CEO   Glaxo Group Limited  BY:
  /s/ Victoria Whyte
  
  Date:
  28thApril 2009NAME:TITLE:  3