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                                                                   EXHIBIT 10.42

                              [SEPRACOR LETTERHEAD]

                                   **REVISED**

VIA FAX & FEDERAL EXPRESS

September 10, 1999

Mr. James O'Shea
4005 Springfield Lane
Greenville, DE 19807

Dear Jim:

It is my pleasure to offer you the position of President and Chief Operating
Officer of Sepracor. This position will report to the Chairman and Chief
Executive Officer of the Company.

In this role, you will be responsible for all commercial operations of Sepracor,
including sales and marketing, business development, distribution, and
production. You will b responsible for the development and execution of the
Annual Operating Plan and will work together with the CEO to develop and
maintain a five-year strategic plan, and play an integral role in all major
strategic initiatives, such as acquisition.

In addition, you will play a major role in directing the Company's investments
in R&D through the establishment of a process of portfolio analysis and
planning.

We are pleased to offer you a salary of $350,000, paid bi-weekly. You will also
receive a yearly bonus of $200,000 paid annually upon achievement of mutually
acceptable goals which we will establish together.

In addition, you will also receive a stock option grant, contingent upon Board
of Directors' approval, for 500,000 shares at a strike price equivalent to the
price of Sepracor common stock at the close of the market on the day of the next
Board of Directors' meeting. 300,000 shares will vest over five years at a rate
of 20% per year, starting on the first anniversary of the option grant. 100,000
shares will begin to vest and will vest over four years at a of 25% per year,
when Sepracor common stock has traded at greater than $150/share for twenty
consecutive trading days. 100,000 shares will begin to vest and will vest over
three years at a rate of 33% per year, when Sepracor common stock has traded at
greater than $200/share for twenty consecutive trading days.

In the event involuntary termination occurs, continuance of your base salary and
benefits will be provided for you for one year from the date of your
termination.

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In the event of a change of control in the ownership of the Company as defined
by greater than 50% ownership of the common shares outstanding, your unvested
stock options would vest on the date of change of control, as per the Company's
Stock Option Plan.

The Company will reimburse you for all reasonable relocation expenses, including
realty and closing costs on the sale and purchase of your current and new house,
respectively, and for moving of household goods.

Jim, I am delighted at the prospect of your joining Sepracor. I look forward to
working together to create an unusually successful company, and to having great
fun at the same time.

Please sign below to indicate your acceptance of this offer.

Very truly yours,

/s/  Timothy J. Barberich

Timothy J. Barberich
Chairman & Chief Executive Officer

ACCEPTED AND AGREED TO HEREIN:

/s/  James O'Shea                                        9/21/99
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James O'Shea                                  Date