EXHIBIT 10.1

July 10, 2006

Michael Tansey, BSc, MB ChB, MD, FFPM
7651 Country Club Drive
La Jolla, CA 92037

Dear Mike:

On behalf of La Jolla Pharmaceutical Company, I am pleased to offer you the
position of Chief Medical Officer. This position will report to Deirdre
Gillespie, M.D. in her position as President & CEO. Your start date will be
Monday, July 17, 2006. Upon joining the Company, as a regular, part-time, exempt
employee on your date of hire, La Jolla Pharmaceutical Company will provide you
with a biweekly salary of $7,673.08 ($199,500.00 annualized figure). This figure
is based on our mutually agreed part time schedule of 65% and is subject to
change should there be a modification to this agreement. Your compensation will
be payable biweekly less payroll deductions and all required withholdings,
effective on your start date. In addition to your regular salary, you will be
eligible to receive a target bonus of up to 35% of your base salary, with any
bonus for year 2006 being prorated. This bonus will be determined by the
achievement of goals tied to your position and the achievement of overall
Corporate goals and is subject to approval by the Company’s Board of Directors.

In addition, La Jolla Pharmaceutical Company’s management will recommend to the
Board of Directors that the Company grant you an incentive stock option to buy
113,000 shares of LJP common stock in accordance with the Company’s current
stock option plan.

Furthermore, La Jolla Pharmaceutical Company agrees to pay you $9,600.00 per
year employed for supplemental medical coverage. As a condition, you will
decline the company’s medical plan during open enrollment periods. La Jolla
Pharmaceutical Company further agrees to reimburse up to $2,500.00 per month for
expenses actually and reasonably incurred by you for temporary housing for a
maximum period of six months from your start date or until such time as you
obtain permanent housing, whichever is earlier, as long as you are employed by
the Company.

You will be eligible for the Company’s vacation, sick leave, holidays, 401k,
medical, dental and vision benefits on your start date. Details about these and
other employee benefit plans are available for your review.

As a La Jolla Pharmaceutical Company employee, you will be expected to abide by
the Company’s rules, policies and regulations, in accordance with our standard
employment practices. Prior to employment, you will be required to sign an
agreement covering the Company’s Invention and Confidential Information. This
offer will also be contingent upon the successful completion of LJP’s background
screening process.

You may terminate your employment with La Jolla Pharmaceutical Company at any
time and for any reason whatsoever, simply by notifying La Jolla Pharmaceutical
Company. Likewise, La Jolla Pharmaceutical Company may terminate your employment
or change your employment status at any time whatsoever, with or without cause
or advance notice. Since La Jolla Pharmaceutical Company’s standard policy does
not provide for agreements guaranteeing employment for any specific period of
time, this offer is not intended to be construed as an employment contract or a
guarantee of benefits.

The employment terms in this letter supersede any other agreements or promises
made to you by anyone, whether oral or written. As required by law, this offer
is subject to satisfactory proof of your right to work in the United States.
Please see the attached Employment Eligibility Verification for a list of
acceptable documents you will need to provide upon within three (3) days of date
of hire.

To accept this offer of employment under the terms described above, please sign
the enclosed Invention and Confidential Information Agreement and one copy of
this letter and return them to me at La Jolla Pharmaceutical Company.

Should you have any questions, please do not hesitate to call. We look forward
to having you join our organization and are confident that this will result in a
mutually advantageous relationship.

Please note that if this offer is not accepted in writing as of Monday, July 17,
2006 at 5:00 p.m. Pacific Standard Time, it will become null and void.

Sincerely,

/s/ Deirdre Gillespie
Deirdre Gillespie, MD
President & CEO

     
/s/ Michael Tansey
  7/14/06
 
   
Michael Tansey, BSc, MB ChB, MD, FFPM
  Date

Enclosures